FOUS11 KWBC 272050
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
350 PM EST Thu Nov 27 2025

Valid 00Z Fri Nov 28 2025 - 00Z Mon Dec 01 2025

...Great Lakes...=20
Day 1...

Long duration lake effect snow (LES) event continues through=20
Friday with prolific snowfall totals in the favored snow belts for
NWly flow in northern MI and for WNWly flow off Lakes Erie and
Ontario.=20

Deep low remains over central Quebec through Friday before lifting
to Labrador. The mid level trough axis associated with the low is
currently over the eastern U.P. and will swing east over the
eastern Lakes tonight. Saturated DGZ zones will maintain efficient
snow production over the autumnally warm lakes. Ridging finally=20
spreads east over the region Friday night ending the LES.=20

For Michigan expect individual banding in NW flow over the eastern
U.P. with additional banding from added fetch from Lake Michigan=20
into the Tip of the Mitt will persist through Friday morning. Day=20
1 WPC snow probs for >8" additional are 40-70% in the same narrow=20
zones being impacted now.=20

Eastern Great Lakes see ideal multiple lake fetch in cyclonic flow as
seen in current radar mosaics with banding from Superior,=20
Michigan, Huron, and Ontario into the Tug Hill and fetch from
Superior, lower Michigan, and Erie into the Chautauqua Ridge of
western NY and east of Cleveland. WPC Day 1 snow probs for >8"
additional are 50-70% for these features, and over 80% on the
Chautauqua Ridge where probs for >12" are 50-70%.

Key Messages remain in effect for this system (link #1 below).


...Northern High Plains through the Midwest into the Northeast...=20
Days 1-3...

...Significant winter storm to impact large portions of the=20
Northern Plains, Midwest, and Great Lakes through this weekend...

A closed low along the WA coast this afternoon will shift southeast
tonight while opening, crossing the Northern Rockies Friday. This=20
wave is shunted on the southern trajectory from a northern stream
trough currently shifting south down the Canadian Rockies tonight.
This trough interaction and a strengthening upstream jet streak=20
will help spread moderate snow bands from Glacier NP through
northern MT tonight. Temperatures will be plenty cold for all snow
in the bands with some freezing rain potential on the southern
portions of precip over south-central MT overnight.=20

The frontogenetical banding quickly extends across the Dakotas
Friday morning, reaching western Iowa in the afternoon. This
banding is north of a developing lee-side low ahead of the merging
troughs that develops over eastern CO Friday and shifts east over
the KS/OK border as it further develops Friday night. This allows
the fgen band to transition into a deformation band around an
inverted trough extending from the surface low. Day 1.5 snow probs
for >6" are 30-60% from Northeast MT through central Iowa.=20

Thereafter, the system amplifies to become much more impressive=20
with expanding heavy precipitation through the central Midwest=20
Friday night through Saturday. The mid-level trough diving into the
Central Plains will sharpen, and as the vort swings into the base=20
of the longer wave trough it will force a negative tilt coincident=20
with the development of coupled jet streaks (one strengthening over
the Central Plains and another exiting the Great Lakes) to produce
strong ascent. This overlapping synoptic lift will help strengthen
a surface low developing in the lee of the CO Rockies and then=20
tracking east, and eventually northeast, from KS through IL and=20
into southern MI by 12Z Sunday.

Downstream of this surface low, warm and moist advection will
rapidly intensify as 850mb winds surging to above 50kts draw
elevated PWs northward from the Gulf, reflected by PW anomalies
surging above the 90th percentile according to NAEFS into KS/MO/IA.
This will be accompanied by a theta-e ridge lifting northward as
well, and although a true TROWAL is not currently progged, this
theta-e ridge will still promote additional moisture and some
elevated warm air to promote modest potential instability. This
intense WAA will help expand precipitation from the Dakotas and=20
Iowa Friday night, to encompass most of the Upper Midwest Saturday,
and then cross Lower Michigan Saturday night before surging up the
Interior Northeast Sunday.

Confidence continues to increase in the track of the low with a
preference for the northern end of the precip shield given to the
EC/GFS which are farther north (through central WI with 0.5" QPF) than
the CMC/UKMET. The broad precip shield and ample cold air will
result in pivoting heavy bands with the highest totals as of now
forecast over central IA where a foot is possible. As noted before
the DGZ depth will be a concern at times and with so much precip
from WAA, the ratios should be somewhat limited over IL/IN ahead of
the system.=20

Day 2/2.5 WPC snow probs for >8" are over 30% from far southeast
SD/northeast Neb across all but far southwest IA, southern MN,
central and southern WI, and northern IL. Day 3 probs for >8" are
20-40% for much of the L.P. of Michigan. Post-Thanksgiving travel=20
is likely to be extremely disrupted during this event.

Key Messages remain in effect for this system (Link #2 below).


...Cascades and Northern Rockies...=20
Days 1-2...

Low crossing WA tonight with snow levels in the Cascades around
5000ft. Pacific moisture surges inland ahead with snow levels over
the northern Rockies of 4000-5000ft which decrease after snow
tapers behind a northern stream trough descending from the Canadian
Rockies. Day 1 snow probs for >6" are 40% in the high WA Cascades=20
and 50-80% across all western MT ranges into northern ID.=20

A combined upper trough shifts down the Rockies Friday with Day 1.5
snow probs for >6" 40-70% in the Tetons, Absarokas, Bighorns, and
ranges of north-central C0.=20


Jackson



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!8umiVbKQN4ZSupkAbsvNAy8egWLsRvjnEIX-waL1s0UKs= _UdFepA7tN5qL700FGj-H401SxDmvGxZyaBuiBN2o7Ywhc$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!8umiVbKQN4ZSupkAbsvNAy8egWLsRvjnEIX-waL1s0UKs= _UdFepA7tN5qL700FGj-H401SxDmvGxZyaBuiBN6Di-u1E$=20




$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 280707
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
207 AM EST Fri Nov 28 2025

Valid 12Z Fri Nov 28 2025 - 12Z Mon Dec 01 2025

...Great Lakes & Northeast...=20
Day 1...

Cyclonic flow aloft will persist a long duration lake effect snow
(LES) event into Saturday morning, with prolific snowfall totals
likely in a few areas.=20

The period begins with an elongated but closed mid-level low
centered over Quebec driving lowered heights into the Northeast.
Rounding the base of this trough, a secondary shortwave and
elongated vorticity lobe will swing eastward through the Great=20
Lakes and into the Northeast tonight, bringing a brief period of=20
shortwave ridging to the area tonight. This will be the evolution=20
to finally shut off the LES.

However, until then, two significantly impactful winter weather
areas are expected. The first is in the favored WNW snow belts off
the Great Lakes: from the eastern U.P. through the NW L.P. of MI,
and then downstream along the Chautauqua Ridge and the Tug Hill
Plateau. 850mb temps falling to as low as -15C (-10C far east
portions) will drive steepening lapse rates across lake
temperatures that are still generally +6C to +10C according to
GLERL. The cooling column will keep the DGZ relatively shallow, but
favorable ascent crossing the DGZ efficiently will produce bands of
very heavy snow for which the HREF indicates has a >60% chance of
exceeding 1"/hr, and will likely reach 2-3"/hr at times in response
to deep inversion depths as high as 700mb. Although winds will
fluctuate just enough to prevent stationary single bands (plus the
fetch direction is not along the long-breadth of the lakes in many
areas), narrow corridors of heavy snow are expected, especially
where any upstream connection can occur from Huron/Superior/Georgian
Bay to Lakes Erie and Ontario. The heaviest snow is likely D1 just
southeast of Lakes Erie and Ontario where WPC probabilities for 8+
inches reach 50-90%, and storm total snowfall from this event=20
could be over 2 feet in a few locations.

In addition to the LES, a strong cold front pressing east from the
Lakes early this morning will reach the Atlantic coast this=20
evening. The guidance has become increasingly excited in the
potential for convective snow showers or snow squalls along this
front, as reflected by a snow-squall parameter well above 1. The
environment appears favorable for snow squalls from western PA
through northern ME as the front passes east, moving across an
environment with SBCAPE as high as 250 J/kg coincident with modest
0-2km fgen and theta-e lapse rates falling below 0C/km. Moisture
may be the limiting factor away from the Great Lakes, so the best
chance for squalls appears to be well inland of these states, but
any place that does receive a squall this afternoon would likely
experience dangerous travel due to rapidly changing conditions with
briefly heavy snow and gusty winds.

Key Messages remain in effect for this system (link #1 below).


...Northern High Plains through the Midwest into the Northeast...=20
Days 1-3...

...Significant winter storm to impact large portions of the=20
Northern Plains, Midwest, and Great Lakes through this weekend...

The first widespread significant winter storm of the season begins
in earnest today as a positively tilted shortwave trough emerges
from the Pacific Northwest and tracks southeast into the
Northern/Central Plains. As a secondary vorticity impulses rotates
into the trough, this will force downstream amplification of the
mid-level pattern, resulting in a negatively tilted trough and
increasing ascent downstream into the Upper Midwest and Great
Lakes. At the same time, jet streaks both upstream and downstream
of this amplifying trough will begin to couple, producing even more
intense deep layer lift, and a surface low will result - first in
the lee of the Rockies and then tracking gradually northeast into
MI by Sunday morning. This low will then continue to deepen as it
shifts across southeast Canada and exits into the Canadian
Maritimes by the end of the forecast period /12Z Monday/.

The guidance has come into much better agreement with the track and
intensity of this system, and while small temporal and spatial
differences among the ensembles still exist, the spread is minimal
compared to previous model runs leading to higher confidence in the
evolution. As the low deepens and moves northeast, impressive WAA
will develop downstream of the developing cyclone, spreading PWs
which will exceed the 90th percentile northward into MO/IA. The
accompanying theta-e ridge will surge in tandem and isentropically
ascent the region, and while guidance is still not suggesting a
strong TROWAL, at least subtle warm air aloft will help develop
modest conditional instability. The coincident and impressive 290K
isentropic ascent will lead to expanding and intensifying
precipitation, with moderate snow likely across much of the
Northern Plains, Upper Midwest, and Great Lakes, especially Friday
night through Sunday morning.

On D1, the heaviest snowfall accumulations are likely in a narrow
band driven by the jet streak aloft and the accompanying
ageostrophic/fgen enhancement between 700-600mb. This will cause a
stripe of periodically heavy snow from southern ND through western
IA, and although the band should be narrow, snowfall rates of
0.5"-1"/hr are likely which could cause 4-6" of snow as reflected
by WPC probabilities for 4+ inches that reach above 70%.

However, the most significant part of this event begins late D1
across IA and then spreads east through D2 into MI. Here, the
impressive isentropic ascent will be quite moist as reflected by
mixing ratios of 4 g/kg on the 290K surface, leading to a rapidly
saturating column. While in general this upglide will result in
moderate snowfall rates, there appears to be an increasing risk for
heavier snowfall across portions of MO/IA/IL as the WAA forces
an increasing isothermal layer beneath the DGZ which also begins to
deepen. Cross-sections are more robust featuring a corridor of
folding theta-es surfaces within the elevated RH, suggesting a
greater potential for CSI and convective snowfall rates. There is
still some uncertainty into this since this signal is much more
robust tonight than previous model runs, but locally 1-2"/hr rates
appear possible which is supported by the WPC prototype snowband
tool despite a modest overall appearance of the evolution with
respect to conceptual models for heavy snow bands. Still, multiple
bands lifting northward for a long duration will result in
significant snowfall accumulations and major impacts for the post-
Thanksgiving holiday travel.=20

This will be a significant system with several waves of moderate to
heavy snowfall. On D2, the heaviest accumulations are expected from
far eastern NE through IA, northern IL, and southern WI. WPC
probabilities in this region are 70-90% for more than 6 inches of
snow, and locally as high as 50% for more than 12 inches, highest
near the Quad Cities of IA. Later D2 into D3 the heaviest snow
shifts eastward and eventually wanes in intensity, but additional
heavy snowfall exceeding 6" is possible, especially around Lake
Michigan and into the L.P. of MI. Event total snowfall may reach
15" in isolated locations Saturday.

Moderate snowfall is also expected across the interior northeast=20
where WPC probabilities D3 are as high as 50-70% for 4+ inches in=20
the higher terrain of VT, NH, and ME.

Key Messages remain in effect for this system (Link #2 below).


...Central Rockies...
Day 3...

A potent shortwave will drop out of the Pacific Northwest Sunday
morning and then move progressively southeast, reaching the Four
Corners Sunday night while maintaining a positive tilt. Late D3
this feature will begin to sharpen, with the resulting downstream
jet streak intensifying into the Central Plains. The overlap of the
RRQ of this jet streak with the greatest height falls ahead of the
trough axis will help spawn low pressure in the Great Basin, and
this low will help to increase ascent across the Central Rockies
Sunday evening. As the overall ascent increases, precipitation will
expand, and periods of moderate to heavy snow are likely, generally
above 5000 ft. This system is expected to remain progressive so
prolonged snowfall is not expected, but WPC probabilities indicate
a moderate risk (50-70% chance) of at least 6 inches of snowfall
across the CO Rockies and northern San Juans, with lighter
accumulations expected as far west as the Wasatch of Utah.


Weiss




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!6Sc2F0cnium5fdExFU2gmXHPKlYB1f8bP0Ql_VmqDRwDR= tO2_L40P2nqWm2GPccQ_EI7PVD0CcUgKaNs5dlLL32TFvQ$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!6Sc2F0cnium5fdExFU2gmXHPKlYB1f8bP0Ql_VmqDRwDR= tO2_L40P2nqWm2GPccQ_EI7PVD0CcUgKaNs5dlLAcOrDGE$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 281854
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
154 PM EST Fri Nov 28 2025

Valid 00Z Sat Nov 29 2025 - 00Z Tue Dec 02 2025

...Great Lakes & Northeast...=20
Day 1...

Persistent cyclonic flow will maintain the current long duration=20
lake effect snow (LES) event into Saturday morning leading to prolific
snowfall totals likely in a few areas.=20

Elongated but closed mid-level low remains centered over Quebec=20
driving lowered heights into the Northeastern CONUS. Rounding the=20
base of this trough, a secondary shortwave and elongated vorticity=20
lobe is swinging eastward through the western Great Lakes,
eventually making headway into the Northeast tonight, bringing a=20
brief period of shortwave ridging to the area overnight. This will=20
be the evolution to finally shut off the LES machine that's been=20
present the past 48+ hours.

However, until that transpires, two significantly impactful winter
weather areas continue through this afternoon and early evening.=20
The first is in the favored WNW snow belts off the Great Lakes:=20
from the eastern U.P. through the NW L.P. of MI, and then
downstream along the Chautauqua Ridge and the Tug Hill Plateau. 18z mesoanalysis indicates a broad expanse of 850mb temps between -10
to -15C, driving steepening lapse rates across lake temperatures
that are still generally +6C to +10C according to GLERL. The
cooling column will keep the DGZ relatively shallow, but favorable
ascent crossing the DGZ efficiently has aided in producing a
plethora of multi-band structures with hourly rates upwards of
1"/hr. Hourly max rates will likely reach 2-3"/hr at times in
response to deep inversion depths as high as 700mb, especially in
the singular band structure from a long fetch axis oriented from
Lake Huron down through Georgian Bay then back over Lake Ontario.
The aforementioned persistent singular band is well-defined at this
hour off Lake Ontario through Oswego county extending into=20
southern Tug Hill and areas downstream. This area will exhibit the=20
heaviest snowfall accumulations through the period with areas=20
residing in the band likely to attain well over 12" at this=20
juncture leading to snowfall totals eclipsing 2ft for the entirety=20
of the event.

In addition to the LES, a strong cold front pressing east from the
Lakes has allowed for convective snow showers or snow squalls=20
along this front. Regional radar composite shows a multitude of
convectively based snow showers/squalls across southern NY state
down through western and central PA. The environment remains
favorable as the front advances east with MUCAPE as high as 200=20
J/kg coincident with modest 0-2km fgen and theta-e lapse rates=20
falling below 0C/km centered over west-central PA as of 18z. Snow
squall warnings have been issued in response over the past few
hrs, a testament to the environmental favor in place. Any area that
receives these snow squalls will encounter the opportunity for=20
dangerous travel due to rapidly changing conditions with briefly=20
heavy snow and gusty winds.

Key Messages remain, but will be the final issuance for the event=20
(link #1 below).


...Northern High Plains through the Midwest into the Northeast...=20
Days 1-3...

...Significant winter storm to impact large portions of the=20
Northern Plains, Midwest, and Great Lakes through this weekend...

The previous forecast discussion remains very relevant for the
incoming significant winter storm development already materializing
over the Plains and Midwest. Latest UA analysis this afternoon
indicates a positively tilted shortwave trough emerging from the=20
Pacific Northwest, forecast to track southeast into the=20
Northern/Central Plains as we continue through this afternoon. As=20
a secondary vorticity impulses rotates into the trough, this will=20
force downstream amplification of the mid-level pattern, resulting=20
in a negatively tilted trough and increasing ascent downstream into
the Midwest and Great Lakes. At the same time, jet streaks both=20
upstream and downstream of this amplifying trough will begin to=20
couple, producing even more intense deep layer lift, and a surface=20
low will result - first in the lee of the Rockies and then tracking
gradually northeast into MI by Sunday morning. This low will then=20
continue to deepen as it shifts across southeast Canada and exits=20
into the Canadian Maritimes by the end of the forecast period /12Z=20
Monday/.

The guidance this morning has maintained general continuity with=20
better agreement on the track and intensity of this system, and=20
while small temporal and spatial differences among the ensembles=20
still exist, the spread is minimal compared to previous model runs=20
leading to a high confidence scenario in both the expected
evolution and snowfall forecast. As the low deepens and moves=20
northeast, impressive WAA will develop downstream of the developing
cyclone, spreading PWs which will exceed the 90th percentile=20
northward into MO/IA. The accompanying theta-e ridge will surge in=20
tandem and isentropically ascent the region, and while guidance is=20
still not suggesting a strong TROWAL, at least subtle warm air=20
aloft will help develop modest conditional instability. The=20
coincident and impressive 290K isentropic ascent will lead to=20
expanding and intensifying precipitation, with moderate snow likely
across much of the Northern Plains, Upper Midwest, and Great=20
Lakes, especially Friday night through Sunday morning.

On D1, the heaviest snowfall accumulations are likely in a narrow
band driven by the jet streak aloft and the accompanying
ageostrophic/fgen enhancement between 700-600mb. This has allowed
for a stripe of periodically heavy snow over parts of the Dakotas,
spreading into western IA as of the past few hrs. Despite the band=20
being relatively narrow, snowfall rates of 0.5"-1"/hr are likely=20
which could cause 4-6" of snow as reflected by WPC probabilities=20
for 4+ inches that reach above 70%.

However, the most significant part of this event begins later this
evening across IA, spreading eastward through D2 IL/WI/MI. Here,=20
the impressive isentropic ascent will be quite moist as reflected=20
by mixing ratios of 4 g/kg on the 290K surface, leading to a=20
rapidly saturating column. While in general this upglide will=20
result in moderate snowfall rates, there appears to be an=20
increasing risk for heavier snowfall across portions of MO/IA/IL as
the WAA forces an increasing isothermal layer beneath the DGZ=20
which also begins to deepen. Cross-sections are more robust=20
featuring a corridor of folding theta-e surfaces within the=20
elevated RH, suggesting a greater potential for CSI and convective=20
snowfall rates. There is still some uncertainty into this since=20
this signal is much more robust tonight than previous model runs,=20
but locally 1-2"/hr rates appear possible which is supported by the
WPC prototype snowband tool despite a modest overall appearance of
the evolution with respect to conceptual models for heavy snow=20
bands. Still, multiple bands lifting northward for a long duration=20
will result in significant snowfall accumulations and major impacts
for the post- Thanksgiving holiday travel.=20

This will be a significant system with several waves of moderate to
heavy snowfall. On D2, the heaviest accumulations are expected from
far eastern NE through IA, northern IL, and southern WI. WPC
probabilities in this region are 70-100% for more than 6 inches of
snow, and locally as high as 50-70% for more than 12 inches,=20
highest near the Cedar Rapids over into the Quad Cities of IA.=20
Later D2 into D3 the heaviest snow shifts eastward and eventually=20
wanes in intensity, but additional heavy snowfall exceeding 6" is=20
possible, especially around Lake Michigan and into the L.P. of MI.=20
Event total snowfall may reach upwards of 15+" in isolated=20
locations Saturday, potentially setting November and even=20
encroaching some all-time snowfall records for the 24hr and 48hr=20
periods.

Moderate snowfall is also expected across the interior northeast=20
where WPC probabilities D3 are as high as 50-70% for 4+ inches in=20
the higher terrain of VT, NH, and ME.

Key Messages remain in effect for this system (Link #2 below).


...Central Rockies...
Day 3...

No changes necessary to the anticipated evolution of the next
winter disturbance to impact the Central Rockies. A potent=20
shortwave will drop out of the Pacific Northwest Sunday morning,
moving progressively southeast, reaching the Four Corners Sunday=20
night while maintaining a positive tilt. Late D3 this feature will=20
begin to sharpen, with the resulting downstream jet streak=20
intensifying into the Central Plains. The overlap of the RRQ of=20
this jet streak with the greatest height falls ahead of the trough=20
axis will help spawn low pressure in the Great Basin, and this low=20
will help to increase ascent across the Central Rockies Sunday=20
evening. As the overall ascent increases, precipitation will=20
expand, and periods of moderate to heavy snow are likely, generally
above 5000 ft. This system is expected to remain progressive so=20
prolonged snowfall is not expected, but WPC probabilities indicate=20
a moderate risk (50-80% chance) of at least 6 inches of snowfall=20
across the CO Rockies and northern San Juans, with lighter=20
accumulations expected as far west as the Wasatch of Utah.


Weiss/Kleebauer


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!9HzmYz-mIE6DfhJQQBQsOzECv_KFcaoJzdylhJVfCiVsb= -Dbu3RKVB1zEOHkADoLaYbeS0vS7lK--9jlNEGcykLqUmg$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!9HzmYz-mIE6DfhJQQBQsOzECv_KFcaoJzdylhJVfCiVsb= -Dbu3RKVB1zEOHkADoLaYbeS0vS7lK--9jlNEGckf1n8zY$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 290825
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
325 AM EST Sat Nov 29 2025

Valid 12Z Sat Nov 29 2025 - 12Z Tue Dec 02 2025


...Northern High Plains through the Midwest into the Northeast...=20
Days 1-2...

...Significant winter storm ramps up across the Midwest today...

A positively tilted shortwave trough diving out of Montana will
sharpen today across the Central Plains, and eventually take on a
negative tilt by this evening in response to secondary vorticity
energy rotating through its base. This evolution will result in
intensifying deep layer ascent in response to more significant
height falls overlapping mid-level divergence, and this will
additionally be aided by increasingly coupled upper jet streaks.
The surface low developing within this impressive ascent will then
deepen as it lifts northeast from Kansas /12Z Saturday/ to Michigan
/12Z Sunday/. This system will become increasingly progressive
through D2, reaching the Canadian Maritimes by 12Z Monday.

This evolution will yield an impressive swath of snow from the
Northern Plains through much of the Midwest and then into the Great
Lakes. As the low develops, increasing warm/moist advection will
surge PWs out of the Gulf, and PW anomalies above the 90th
percentile are progged by NAEFS to reach as far north as MO/IA.
This will occur during a period of intensifying 290K isentropic
ascent, which when occurring beneath the larger scale synoptic lift
will cause snowfall to expand quickly, and become heavy, especially
where 700-600mb fgen intensifies (both due to the WAA and the
ageostrophic response of the upper jet position). At the same time, cross-sections continue to indicate a threat for CSI due to folding
theta-e surfaces, which additionally will support periods of heavy
snowfall rates as laterally translating bands shift northeast
through the region. Snowfall rates of 1-2"/hr are likely (>80%
chance according to the HREF), which, although won't be constant,
will help rapidly accumulate snowfall even with SLRs that will be
around to slightly below climo most of the event.

This intense snowfall will result in widespread significant
impacts, and the WSSI-P indicates a 60-80% chance of major impacts
for parts of IA, IL, and WI, including the Des Moines, Chicago, and
Milwaukee metro areas. This will snarl travel during the busy
post-Thanksgiving holiday weekend. Where snow is the most intense
and longest lasting, record or near-record November snowfall is
possible, especially across eastern IA, southern WI, and northern
IL. This is also where the ECMWF EFI is above 0.9 with an SoT of
1-5, further indicating the potentially record-breaking November
snowfall.

WPC probabilities D1 are high (>70%) for at least 6" of snow from=20
central IA though southern MI, with locally more than 12" possible
(10-30% chance) in eastern IA, southern WI, and northern IL.
Isolated higher totals are possible as well where any banding can
persist due to local convergent features such as indicated by many
of the high-res models near Lake Michigan.

The most significant snowfall should wane quickly from west to east
by 12Z Sunday, but post-system NW flow will create some modest lake
effect snow (LES) across the U.P. and L.P. of MI, as well as east
of Lakes Erie and Ontario Sunday night. Additionally, some modest warm-advection snowfall is likely across the higher terrain of the
interior Northeast before snowfall comes to an end by 12Z Monday.
Additionally snowfall of more than 4 inches is likely (50-90%
chance) according to WPC probabilities from the Chautauqua Ridge
northeast through the higher terrain of the Adirondacks, and into
VT/NH/ME.

Key Messages remain in effect for this system (Key Message 2=20
below).


...Central Rockies through the Mid-Mississippi Valley...=20
Days 2-3...

The next system follows quickly behind the powerful storm across
the Midwest as progressive flow dominates the CONUS.

This system begins as a positively tilted shortwave emerging from
the Pacific Northwest and then digging rapidly into the Four
Corners states by 12Z Monday. As this impulse dives southeast, the
associated vorticity lobe will swing rapidly east, forcing the
evolution into a neutral tilt over the Central/Southern Plains D3,
and potentially becoming negatively tilted late in the forecast
period across the Mid-Mississippi Valley. During this evolution, a
downstream upper jet streak will amplify and pivot poleward over
the Central Plains to enhance deep layer lift. This should cause an
area of heavy snowfall D2 across the Central Rockies, including=20
the Wasatch, Uintas, and CO Rockies where snow levels of around
4000-5000 ft are expected. Although the system is progressive, PW
anomalies above the 90th percentile will support periods of heavy
snow, aided by upslope into the terrain, and WPC probabilities for
more than 4 inches of snow have increased to 70-90% across the Ruby
Mountains in NV, as well as the expanse of the Wasatch, Uintas, CO
Rockies, and San Juans. Locally as much as 12" of snow is possible
in the highest terrain of Colorado.

The forecast becomes more challenging into D3 as this system=20
pushes east. Although the surface wave is likely to wane across the Southern/Central Plains, the downstream impressive jet streak and=20
height falls invof the upper trough will persist. Late Monday, some
of the guidance indicates that the downstream jet and a secondary=20 sub-tropical jet streak emerging across Mexico will phase, leading=20
to secondary low pressure development across the Mississippi=20
Valley. As this occurs, precipitation will expand from the Gulf=20
Coast through the Mid-Mississippi Valley in response to=20
intensifying moist isentropic ascent along the 290K-300K surfaces.=20
Mixing ratios within this plume are progged at 4-8 g/kg, around the
75th-90th percentile for the date, indicative of the impressive
moisture availability in this system.=20

While there are still important timing, location, and thermal=20
differences among the various global members and their associated=20
ensembles, the trends are for a wetter and colder system which=20
could produce significant snow and mixed precipitation before 12Z=20
Tuesday. The AIFS and ECMWF EFI are both well southeast of the=20
highest NBM probabilities during D3, but the D3/D4 clusters=20
indicate high variability due to timing differences of the trough.=20
Despite this uncertainty, current WPC probabilities for at least 2"
of snow are moderate (30-70% chance) from central Kansas through=20
the western Ohio River Valley, with the potent jet streak aloft=20
helping to produce potential banded snow in this region.=20

Additionally, with warm moist air flooding northward from the Gulf
and a retreating cold high pressure in place, a zone of mixed
precipitation, including freezing rain, is likely from the Ozarks
through the southern Appalachians. There continues to be much
uncertainty in the axis of heaviest ice accretions, but
probabilities for at least some modest ice have come up tonight,
leading to increasing confidence in areas of impactful freezing
rain. At this time, WPC probabilities for 0.1" on D3 are as high as
30% in the Ozarks, and 30-50% in the southern Appalachians.

This system will likely continue beyond this forecast period while strengthening, and may create heavy snow across the interior Mid-
Atlantic and Northeast on Tuesday. For this reason, key messages
have been initiated (Key Message 3 below).


Weiss


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!6AjAsWQpkfwy645ER6VQR0wLShDHv63j-1-CD6L3akHfB= DlClvSPq3DonTR_1NKPbrp6WnFzXPoiq9k9rUpb3aiBrZE$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_3.png__;!!DZ3fjg!6AjAsWQpkfwy645ER6VQR0wLShDHv63j-1-CD6L3akHfB= DlClvSPq3DonTR_1NKPbrp6WnFzXPoiq9k9rUpbkFb3CDg$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 290829
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 AM EST Sat Nov 29 2025

Valid 12Z Sat Nov 29 2025 - 12Z Tue Dec 02 2025


...Northern High Plains through the Midwest into the Northeast...=20
Days 1-2...

...Significant winter storm ramps up across the Midwest today...

A positively tilted shortwave trough diving out of Montana will
sharpen today across the Central Plains, and eventually take on a
negative tilt by this evening in response to secondary vorticity
energy rotating through its base. This evolution will result in
intensifying deep layer ascent in response to more significant
height falls overlapping mid-level divergence, and this will
additionally be aided by increasingly coupled upper jet streaks.
The surface low developing within this impressive ascent will then
deepen as it lifts northeast from Kansas /12Z Saturday/ to Michigan
/12Z Sunday/. This system will become increasingly progressive
through D2, reaching the Canadian Maritimes by 12Z Monday.

This evolution will yield an impressive swath of snow from the
Northern Plains through much of the Midwest and then into the Great
Lakes. As the low develops, increasing warm/moist advection will
surge PWs out of the Gulf, and PW anomalies above the 90th
percentile are progged by NAEFS to reach as far north as MO/IA.
This will occur during a period of intensifying 290K isentropic
ascent, which when occurring beneath the larger scale synoptic lift
will cause snowfall to expand quickly, and become heavy, especially
where 700-600mb fgen intensifies (both due to the WAA and the
ageostrophic response of the upper jet position). At the same time, cross-sections continue to indicate a threat for CSI due to folding
theta-e surfaces, which additionally will support periods of heavy
snowfall rates as laterally translating bands shift northeast
through the region. Snowfall rates of 1-2"/hr are likely (>80%
chance according to the HREF), which, although won't be constant,
will help rapidly accumulate snowfall even with SLRs that will be
around to slightly below climo most of the event.

This intense snowfall will result in widespread significant
impacts, and the WSSI-P indicates a 60-80% chance of major impacts
for parts of IA, IL, and WI, including the Des Moines, Chicago, and
Milwaukee metro areas. This will snarl travel during the busy
post-Thanksgiving holiday weekend. Where snow is the most intense
and longest lasting, record or near-record November snowfall is
possible, especially across eastern IA, southern WI, and northern
IL. This is also where the ECMWF EFI is above 0.9 with an SoT of
1-5, further indicating the potentially record-breaking November
snowfall.

WPC probabilities D1 are high (>70%) for at least 6" of snow from=20
central IA though southern MI, with locally more than 12" possible
(10-30% chance) in eastern IA, southern WI, and northern IL.
Isolated higher totals are possible as well where any banding can
persist due to local convergent features such as indicated by many
of the high-res models near Lake Michigan.

The most significant snowfall should wane quickly from west to east
by 12Z Sunday, but post-system NW flow will create some modest lake
effect snow (LES) across the U.P. and L.P. of MI, as well as east
of Lakes Erie and Ontario Sunday night. Additionally, some modest warm-advection snowfall is likely across the higher terrain of the
interior Northeast before snowfall comes to an end by 12Z Monday.
Additionally snowfall of more than 4 inches is likely (50-90%
chance) according to WPC probabilities from the Chautauqua Ridge
northeast through the higher terrain of the Adirondacks, and into
VT/NH/ME.

Key Messages remain in effect for this system (Key Message 2=20
below).


...Central Rockies through the Ohio Valley...=20
Days 2-3...

The next system follows quickly behind the powerful storm across
the Midwest as progressive flow dominates the CONUS.

This system begins as a positively tilted shortwave emerging from
the Pacific Northwest and then digging rapidly into the Four
Corners states by 12Z Monday. As this impulse dives southeast, the
associated vorticity lobe will swing rapidly east, forcing the
evolution into a neutral tilt over the Central/Southern Plains D3,
and potentially becoming negatively tilted late in the forecast
period across the Mid-Mississippi Valley. During this evolution, a
downstream upper jet streak will amplify and pivot poleward over
the Central Plains to enhance deep layer lift. This should cause an
area of heavy snowfall D2 across the Central Rockies, including=20
the Wasatch, Uintas, and CO Rockies where snow levels of around
4000-5000 ft are expected. Although the system is progressive, PW
anomalies above the 90th percentile will support periods of heavy
snow, aided by upslope into the terrain, and WPC probabilities for
more than 4 inches of snow have increased to 70-90% across the Ruby
Mountains in NV, as well as the expanse of the Wasatch, Uintas, CO
Rockies, and San Juans. Locally as much as 12" of snow is possible
in the highest terrain of Colorado.

The forecast becomes more challenging into D3 as this system=20
pushes east. Although the surface wave is likely to wane across the Southern/Central Plains, the downstream impressive jet streak and=20
height falls invof the upper trough will persist. Late Monday, some
of the guidance indicates that the downstream jet and a secondary=20 sub-tropical jet streak emerging across Mexico will phase, leading=20
to secondary low pressure development across the Mississippi=20
Valley. As this occurs, precipitation will expand from the Gulf=20
Coast through the Mid-Mississippi Valley in response to=20
intensifying moist isentropic ascent along the 290K-300K surfaces.=20
Mixing ratios within this plume are progged at 4-8 g/kg, around the
75th-90th percentile for the date, indicative of the impressive
moisture availability in this system.=20

While there are still important timing, location, and thermal=20
differences among the various global members and their associated=20
ensembles, the trends are for a wetter and colder system which=20
could produce significant snow and mixed precipitation before 12Z=20
Tuesday. The AIFS and ECMWF EFI are both well southeast of the=20
highest NBM probabilities during D3, but the D3/D4 clusters=20
indicate high variability due to timing differences of the trough.=20
Despite this uncertainty, current WPC probabilities for at least 2"
of snow are moderate (30-70% chance) from central Kansas through=20
the western Ohio River Valley, with the potent jet streak aloft=20
helping to produce potential banded snow in this region.=20

Additionally, with warm moist air flooding northward from the Gulf
and a retreating cold high pressure in place, a zone of mixed
precipitation, including freezing rain, is likely from the Ozarks
through the southern Appalachians. There continues to be much
uncertainty in the axis of heaviest ice accretions, but
probabilities for at least some modest ice have come up tonight,
leading to increasing confidence in areas of impactful freezing
rain. At this time, WPC probabilities for 0.1" on D3 are as high as
30% in the Ozarks, and 30-50% in the southern Appalachians.

This system will likely continue beyond this forecast period while strengthening, and may create heavy snow across the interior Mid-
Atlantic and Northeast on Tuesday. For this reason, key messages
have been initiated (Key Message 3 below).


Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!9tHzHRjIkt5Wlu4_tiXy9Sv1ZC2dufc5i37Fx8TxUhNW7= OiJVNq0TjnWroPuqfJkGLQTip36UtlIlRHH1vKCqFKDIUk$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_3.png__;!!DZ3fjg!9tHzHRjIkt5Wlu4_tiXy9Sv1ZC2dufc5i37Fx8TxUhNW7= OiJVNq0TjnWroPuqfJkGLQTip36UtlIlRHH1vKCQsKH6jU$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 292024
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
324 PM EST Sat Nov 29 2025

Valid 00Z Sun Nov 30 2025 - 00Z Wed Dec 03 2025


...Northern High Plains through the Midwest into the Northeast...=20
Days 1-2...

...Significant winter storm unfolding across the Midwest today...

A pair of 500mb vorticity maximums are interacting with one another
and helping to carve out a negatively-tilted 250-500mb layer trough
over the Midwest this afternoon. A coupled 250mb jet streak setup
is further strengthening the ongoing storm system at the surface,
while at the same time, strong 850-700mb WAA ahead of the storm is
promoting 290K isentropic glide over the Midwest that is fostering
highly saturated profiles within a mesoscale environment that is
ripe for heavy snow bands. ECMWF ensembles show S-SWrly 850mb winds
in excess of 60 kts over the Middle MS Valley, which are topping=20
the 99.5 climatological percentile for late Nov and early Dec. This
exceptional LLJ is feeding a slug of 850-500mb moisture northward=20
that will wrap around the storm system and sufficiently saturate=20
the DGZ over the Midwest. WPC's Snowband Probability Tracker, which
utilizes HREF members, shows a band of 1-2"/hr snowfall rates from
central IA today that heads east across the MS River and towards=20
the Great Lakes this evening.=20

Snow will persist throughout the Great Lakes tonight with snow=20
arriving over the Northeast and central Appalachians Sunday=20
morning. LES bands will develop within broad cyclonic flow off=20
Lakes Superior and Michigan and continue through Sunday evening.
LES bands will stick around a little longer downwind of Lakes Erie
and Ontario but eventually taper off by Monday morning as high
pressure moves in. Locally heavy snowfall is possible in parts of=20
the Tug Hill on Sunday, as well as the White Mountains above
2,000ft where steady SWrly upslope flow within an atmosphere
remaining sub-freezing.=20

WPC probabilities depict moderate-to-hgih chances (50-80%) for
additional snowfall totals >6" along and east of the MS River from
eastern IA and southern MN to the Mitten of Michigan. There are
some low chance probabilities (10-30%) for snowfall totals
exceeding 12" in coastal areas of southeast WI, the Chicagoland
metro area, southwest MI, and northern IN where LES bands may
contribute enough snowfall to where over a foot of snow has
accumulated by the time the LES machine concludes. Downwind of Lake
Erie, parts of the Chautauqua Ridge have moderate chances (40-60%)
for snowfall totals >4" through Monday Sunday night. In the
Northeast, the Tug Hill and White Mountains sport moderate-to-high
chances (50-80%) for snowfall accumulations >6" with localized=20
totals approaching 12" possible by the time this winter storm=20
concludes. The WSSI continues to summarize this storm well,=20
highlighting Moderate to locally Major impacts from central IA on=20
east through the Milwaukee/Chicago metro areas and into northern IN
and southern MI. Expect considerable disruptions to travel in=20
these areas as travelers are likely to encounter numerous travels=20
delays by both road and by air today and lingering through tonight.

Key Messages remain in effect for this system (Key Message 2=20
below).


...Central Rockies through the Ohio Valley, Ice in the Ozarks...=20
Days 2-3...

A positively titled 500mb trough diving south from the Northwest
into the Central Rockies on Sunday will contain both sufficient
synoptic-scale lift and 700-300mb mean layer moisture to support
rounds of mountain snow from central OR and the northern Great
Basin on east across the Wasatch and into the CO Rockies. The
heavier totals in the Great Basin and Wasatch will generally=20
reside above 8,000ft, while the CO/northern NM Rockies are most=20
likely to see their heavier snowfall totals above 9,000ft. WPC=20
probabilities show these listed elevations as having >50% chances=20
for snowfall >8" with localized totals >12" in the peaks of the CO=20 Rockies.=20

As snow continues across the Central Rockies Sunday night, the
aforementioned 500mb trough will begin to eject east into the
Central Plains. A strengthening surge in 700mb WAA and the 500mb=20
PVA will foster a blossoming area of snowfall from the central
Plains to the Middle MS Valley. Snowfall totals are most likely to
range between a coating-3", although WPC probabilities do show low
chances (10-30%) for snowfall totals >4" over northeast KS,
southeast NE, and northern MO through Monday morning. This narrow=20
plume of snow races east across the Lower Great Lakes and OH Valley
Monday evening with similar snowfall totals.

Farther south, as low-level WAA and moisture over-run an air-mass
that features sub-freezing temperatures and dry dew points, a setup
for freezing rain unfolds from the ArkLaTex on across much of AR,
northern MS, western TN, and southern MO. The plume of low-level
moisture does not last too long, but 290K isentropic ascent sticks
around long enough for some disruptive ice accumulations in parts
of these areas on Monday. WPC probabilities show low chances
(10-30%) for ice accumulations over a tenth of and inch, but there
are moderate chances (40-60%) for at least a hundredth of an inch.
The WSSI-P does show up to 40% odds for Minor Impacts as a result
of this freezing rain setup on Monday across much of central AR.=20


...Central Appalachians, Mid-Atlantic, & Northeast...
Day 3-3.5...

...A complex & potentially disruptive winter storm to affect these
regions on Tuesday and into Tuesday night...

Summary: The first accumulating snowfall and disruptive ice event=20
of the season is likely to occur from the Central Appalachians and=20
interior Mid-Atlantic to the Northeast. There remain ongoing=20
changes and disagreements in guidance with snowfall totals, who=20
sees the heaviest totals, and timing all still lower in confidence.
Those in these regions should monitor the forecast from WPC and=20
their local WFOs over the next 24-48 hours.=20

Analysis: As the Central Plains disturbance tracks east Monday=20
evening, there are three other disturbances that are influencing=20
this complicated setup. The first is a weak feature over South TX=20
that is running just out in front of the main upper trough over the
Central Plains. Second: a fast moving 500mb trough over south-=20
central Canada racing southeastward through the Great Lakes by=20
Monday night. Third:the departing system over the Northeast on=20
Monday that races east of Atlantic Canada Monday night. Where=20
guidance is in agreement is that the primary trough over the=20
Central Plains works in tandem with the ejecting Deep South=20
disturbance to direct a plume of 700-300mb moisture at the East=20
Coast. This moisture source will overrun a residual sub-freezing=20
air-mass Monday night over the Central Appalachians and Mid-=20
Atlantic that will support disruptive ice accumulations. However,=20
the dome of high pressure is departing as the storm approaches. For
areas west and north of I-95 in the Mid-Atlantic, boundary layer=20
wet-bulb temperatures will support at least a brief period for=20
accumulating snow. By 18Z Tuesday, a coupling 500mb jet streak=20
setup will support strong vertical ascent aloft that deepens a=20
coastal low as it tracks off the coast. To the north of the storm=20
track, heavy-banded precipitation to the north of a 850-700mb FGEN
band will transpire with snow most likely to occur north of I-95=20
in the higher terrain.

This is where the agreements in the overall setup end. Guidance
members such as the ECMWF show a less amplified Middle MS Valley
feature and less phasing with the Great Lakes disturbance, with
that Great Lakes feature suppressing the storm tracks with its
ensemble membership over the GEFS. Meanwhile, the GEPS are north
and more amplified compared to the GEFS, making the GEFS the
middle ground in storm position. Notably, the EC-AIFS ensemble
means is stronger with the surface low as it reaches the East=20
Coast on Tuesday and its QPF footprint is farther up the coast than
the EPS membership is. At the moment, the ECMWF is on the drier=20
side of guidance, while other like the CMC/NAM are much more=20
amplified. What today's trends have favored, as of this discussion,
is a slightly faster solution that would allow for precipitation=20
to arrive sooner on Tuesday morning.=20

With the cold air-mass retreating on Tuesday, the expectations for
those from northern VA and northern MD on north and east through=20
southeast PA, the Delaware Valley, and into southern New England
was to favor lower SLRs, which should make for a heavy/wet snow.=20
That said, the storm track is critical in determining how far north
the rain/snow line gets. As is the case in marginal boundary layer
temperature environments with fast moving coastal lows that are=20
unable to develop a robust deformation zone, plus baking in=20
climatology for the time of year, it should be the higher=20
elevations north and west of I-95 that are most favored for=20
accumulating snowfall. This setup favors interior New England for=20
heavy snow, although should the Great Lakes disturbance act to=20
suppress the storm track, this could shift farther south to the=20
Catskills and higher terrain of southern New England.=20

WPC probabilities show moderate-to-high chances (50-70%) for=20
snowfall totals >4" from east-central PA on north and east through=20
the Poconos, Catskills, Berkshires, Green, and White Mountains.=20
Farther south, the Philly/Baltimore/DC metro areas may start out=20
briefly as snow, but transition to a wintry mix on Tuesday. There=20
is a possibility for a more icy scenario should cold-air damming=20
(CAD) stick around longer on Tuesday before transitioning to plain
rain. Speaking of CAD, the Central Appalachians will see sub-=20
freezing surface temperatures persist long enough to support a=20
treacherous freezing rain event. WPC probabilities depict=20
moderate-to-high chances (50-80%) for ice accumulations over a=20
tenth of an inch from the Blue Ridge of western NC on north through
the WV/VA Appalachians and Shenandoah Valley with low chances=20
(10-30%) for over a quarter inch of ice. The WSSI-P shows a swath=20
of >50% chances for Minor Impacts from the Central Appalachians on=20
north and east through the WV Panhandle, along and west of Parrs'=20
Ridge in northern MD, through east-central PA, northern NJ, southern
NY, and the interior areas of New England. Key messages are=20
ongoing for this system (Key Message 3 below).=20


Mullinax


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!-II4-v4O3ltIgIqqc2v258ylBcED4sbm6CU-CkNDfY5qL= K4MAm3zknjfJhB255Hjom1Yu-Xc5gaRSOypkDlfvV8Ix70$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_3.png__;!!DZ3fjg!-II4-v4O3ltIgIqqc2v258ylBcED4sbm6CU-CkNDfY5qL= K4MAm3zknjfJhB255Hjom1Yu-Xc5gaRSOypkDlfOJ_EuZY$=20




$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 292040
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 PM EST Sat Nov 29 2025

Valid 00Z Sun Nov 30 2025 - 00Z Wed Dec 03 2025


...Northern High Plains through the Midwest into the Northeast...=20
Days 1-2...

...Significant winter storm unfolding across the Midwest today...

A pair of 500mb vorticity maximums are interacting with one another
and helping to carve out a negatively-tilted 250-500mb layer trough
over the Midwest this afternoon. A coupled 250mb jet streak setup
is further strengthening the ongoing storm system at the surface,
while at the same time, strong 850-700mb WAA ahead of the storm is
promoting 290K isentropic glide over the Midwest that is fostering
highly saturated profiles within a mesoscale environment that is
ripe for heavy snow bands. ECMWF ensembles show S-SWrly 850mb winds
in excess of 60 kts over the Middle MS Valley, which are topping=20
the 99.5 climatological percentile for late Nov and early Dec. This
exceptional LLJ is feeding a slug of 850-500mb moisture northward=20
that will wrap around the storm system and sufficiently saturate=20
the DGZ over the Midwest. WPC's Snowband Probability Tracker, which
utilizes HREF members, shows a band of 1-2"/hr snowfall rates from
central IA today that heads east across the MS River and towards=20
the Great Lakes this evening.=20

Snow will persist throughout the Great Lakes tonight with snow=20
arriving over the Northeast and central Appalachians Sunday=20
morning. LES bands will develop within broad cyclonic flow off=20
Lakes Superior and Michigan and continue through Sunday evening.
LES bands will stick around a little longer downwind of Lakes Erie
and Ontario but eventually taper off by Monday morning as high
pressure moves in. Locally heavy snowfall is possible in parts of=20
the Tug Hill on Sunday, as well as the White Mountains above
2,000ft where steady SWrly upslope flow within an atmosphere
remaining sub-freezing.=20

WPC probabilities depict moderate-to-hgih chances (50-80%) for
additional snowfall totals >6" along and east of the MS River from
eastern IA and southern MN to the Mitten of Michigan. There are
some low chance probabilities (10-30%) for snowfall totals
exceeding 12" in coastal areas of southeast WI, the Chicagoland
metro area, southwest MI, and northern IN where LES bands may
contribute enough snowfall to where over a foot of snow has
accumulated by the time the LES machine concludes. Downwind of Lake
Erie, parts of the Chautauqua Ridge have moderate chances (40-60%)
for snowfall totals >4" through Monday Sunday night. In the
Northeast, the Tug Hill and White Mountains sport moderate-to-high
chances (50-80%) for snowfall accumulations >6" with localized=20
totals approaching 12" possible by the time this winter storm=20
concludes. The WSSI continues to summarize this storm well,=20
highlighting Moderate to locally Major impacts from central IA on=20
east through the Milwaukee/Chicago metro areas and into northern IN
and southern MI. Expect considerable disruptions to travel in=20
these areas as travelers are likely to encounter numerous travels=20
delays by both road and by air today and lingering through tonight.

Key Messages remain in effect for this system (Key Message 2=20
below).


...Central Rockies through the Ohio Valley, Ice in the Ozarks...=20
Days 2-3...

A positively titled 500mb trough diving south from the Northwest
into the Central Rockies on Sunday will contain both sufficient
synoptic-scale lift and 700-300mb mean layer moisture to support
rounds of mountain snow from central OR and the northern Great
Basin on east across the Wasatch and into the CO Rockies. The
heavier totals in the Great Basin and Wasatch will generally=20
reside above 8,000ft, while the CO/northern NM Rockies are most=20
likely to see their heavier snowfall totals above 9,000ft. WPC=20
probabilities show these listed elevations as having >50% chances=20
for snowfall >8" with localized totals >12" in the peaks of the CO=20 Rockies.=20

As snow continues across the Central Rockies Sunday night, the
aforementioned 500mb trough will begin to eject east into the
Central Plains. A strengthening surge in 700mb WAA and the 500mb=20
PVA will foster a blossoming area of snowfall from the central
Plains to the Middle MS Valley. Snowfall totals are most likely to
range between a coating-3", although WPC probabilities do show low
chances (10-30%) for snowfall totals >4" over northeast KS,
southeast NE, and northern MO through Monday morning. This narrow=20
plume of snow races east across the Lower Great Lakes and OH Valley
Monday evening with similar snowfall totals.

Farther south, as low-level WAA and moisture over-run an air-mass
that features sub-freezing temperatures and dry dew points, a setup
for freezing rain unfolds from the ArkLaTex on across much of AR,
northern MS, western TN, and southern MO. The plume of low-level
moisture does not last too long, but 290K isentropic ascent sticks
around long enough for some disruptive ice accumulations in parts
of these areas on Monday. WPC probabilities show low chances
(10-30%) for ice accumulations over a tenth of and inch, but there
are moderate chances (40-60%) for at least a hundredth of an inch.
The WSSI-P does show up to 40% odds for Minor Impacts as a result
of this freezing rain setup on Monday across much of central AR.=20


...Central Appalachians, Mid-Atlantic, & Northeast...
Day 3-3.5...

...A complex & potentially disruptive winter storm to affect these
regions on Tuesday and into Tuesday night...

Summary: The first accumulating snowfall and disruptive ice event=20
of the season is likely to occur from the Central Appalachians and=20
interior Mid-Atlantic to the Northeast. There remain ongoing=20
changes and disagreements in guidance with snowfall totals, who=20
sees the heaviest totals, and timing all still lower in confidence.
Those in these regions should monitor the forecast from WPC and=20
their local WFOs over the next 24-48 hours.=20

Analysis: As the Central Plains disturbance tracks east Monday=20
evening, there are three other disturbances that are influencing=20
this complicated setup. The first is a weak feature over South TX=20
that is running just out in front of the main upper trough over the
Central Plains. Second: a fast moving 500mb trough over south-=20
central Canada racing southeastward through the Great Lakes by=20
Monday night. Third:the departing system over the Northeast on=20
Monday that races east of Atlantic Canada Monday night. Where=20
guidance is in agreement is that the primary trough over the=20
Central Plains works in tandem with the ejecting Deep South=20
disturbance to direct a plume of 700-300mb moisture at the East=20
Coast. This moisture source will overrun a residual sub-freezing=20
air-mass Monday night over the Central Appalachians and Mid-=20
Atlantic that will support disruptive ice accumulations. However,=20
the dome of high pressure is departing as the storm approaches. For
areas west and north of I-95 in the Mid-Atlantic, boundary layer=20
wet-bulb temperatures will support at least a brief period for=20
accumulating snow. By 18Z Tuesday, a coupling 500mb jet streak=20
setup will support strong vertical ascent aloft that deepens a=20
coastal low as it tracks off the coast. To the north of the storm=20
track, heavy-banded precipitation to the north of a 850-700mb FGEN
band will transpire with snow most likely to occur north of I-95=20
in the higher terrain.

This is where the agreements in the overall setup end. Guidance
members such as the ECMWF show a less amplified Middle MS Valley
feature and less phasing with the Great Lakes disturbance, with
that Great Lakes feature suppressing the storm tracks with its
ensemble membership over the GEFS. Meanwhile, the GEPS are north
and more amplified compared to the GEFS, making the GEFS the
middle ground in storm position. Notably, the EC-AIFS ensemble
means is stronger with the surface low as it reaches the East=20
Coast on Tuesday and its QPF footprint is farther up the coast than
the EPS membership is. At the moment, the ECMWF is on the drier=20
side of guidance, while other like the CMC/NAM are much more=20
amplified. What today's trends have favored, as of this discussion,
is a slightly faster solution that would allow for precipitation=20
to arrive sooner on Tuesday morning.=20

With the cold air-mass retreating on Tuesday, the expectations for
those from northern VA and northern MD on north and east through=20
southeast PA, the Delaware Valley, and into southern New England
was to favor lower SLRs, which should make for a heavy/wet snow.=20
That said, the storm track is critical in determining how far north
the rain/snow line gets. As is the case in marginal boundary layer
temperature environments with fast moving coastal lows that are=20
unable to develop a robust deformation zone, plus baking in=20
climatology for the time of year, it should be the higher=20
elevations north and west of I-95 that are most favored for=20
accumulating snowfall. This setup favors interior New England for=20
heavy snow, although should the Great Lakes disturbance act to=20
suppress the storm track, this could shift farther south to the=20
Catskills and higher terrain of southern New England.=20

WPC probabilities show moderate-to-high chances (50-70%) for=20
snowfall totals >4" from east-central PA on north and east through=20
the Poconos, Catskills, Berkshires, Green, and White Mountains.=20
Farther south, the Philly/Baltimore/DC metro areas may start out=20
briefly as snow, but transition to a wintry mix on Tuesday. There=20
is a possibility for a more icy scenario should cold-air damming=20
(CAD) stick around longer on Tuesday before transitioning to plain
rain. Speaking of CAD, the Central Appalachians will see sub-=20
freezing surface temperatures persist long enough to support a=20
treacherous freezing rain event. WPC probabilities depict=20
moderate-to-high chances (50-80%) for ice accumulations over a=20
tenth of an inch from the Blue Ridge of western NC on north through
the WV/VA Appalachians and Shenandoah Valley with low chances=20
(10-30%) for over a quarter inch of ice. The WSSI-P shows a swath=20
of >50% chances for Minor Impacts from the Central Appalachians on=20
north and east through the WV Panhandle, along and west of Parrs'=20
Ridge in northern MD, through east-central PA, northern NJ,
southern NY, and interior New England. Key messages are ongoing=20
for this system (Key Message 3 below).=20


Mullinax



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!_sInBjlekP6pjNLeRE9LcvsU1nax_MbMvx1zivFGkr4Rq= k-U2PID8H1T0KDpJqo1tgG6WZCgot_ZewEEuM12DI18XNw$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_3.png__;!!DZ3fjg!_sInBjlekP6pjNLeRE9LcvsU1nax_MbMvx1zivFGkr4Rq= k-U2PID8H1T0KDpJqo1tgG6WZCgot_ZewEEuM12uPpTWiE$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 300739
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
239 AM EST Sun Nov 30 2025

Valid 12Z Sun Nov 30 2025 - 12Z Wed Dec 03 2025


...Great Lakes to the Interior Northeast...
Day 1...

The major winter storm plaguing the Upper Midwest will wane as the
parent shortwave de-amplifies into a positive tilt and becomes more
embedded in the westerlies across Canada. This will cause a more
rapid progression of the driving low pressure, leading to moderate
continued snow accumulations across the Great Lakes, and expanding
across the higher terrain of the interior Northeast.

The surface low is progged to track from the L.P. of Michigan this
morning into the Canadian Maritimes by Monday morning /end of D1/.
This will result in two areas of additional snowfall accumulation.=20

The first is expected across the Great Lakes as NW flow develops in
the wake of the surface low. While brief deformation snow is likely
as the low departs Michigan, most of the additional snowfall is
likely to be of the lake effect snow (LES) variety as CAA
strengthens across the lakes. 850mb temps falling to -10C or lower
will support steep lapse rates and inversion depths rising to
around 800mb to support at least a brief period of heavy LES with
rates exceeding 1"/hr (40-60% chance from the HREF). The most
likely belts of heavy LES D1 will be across the eastern U.P., the
northern L.P., SW MI, and then east of Lake Ontario. In these
areas, WPC probabilities are 50-70% for more than 4 inches, with=20
locally as much as 8 inches east of Lake Ontario.

The other area of heavy snow from this system will be across the
higher terrain of Upstate NY and Northern New England. WAA
expanding northward downstream of the surface low will spread into
Canada, drawing a narrow column of moisture from the Gulf to cause
expanding precipitation in New England. The WAA is impressive but
transient, and regional forecast soundings suggest persistent mid-
level dry air which will somewhat preclude precipitation rate
intensity. Additionally, the cold high pressure over the region
early will rapidly retreat east, leading to funneled southerly=20
flow with no cold air entrenchment. This suggests that the heaviest
snow will be confined only to the higher terrain of the=20
Adirondacks, Greens, and Whites, where WPC probabilities are=20
moderate (30-50%) for 4+ inches of snowfall.


...Central Rockies/Four Corners...
Days 1-2...

A closed 500mb low dropping out of the Interior Northwest will move progressively southeast today while opening into a positively
tilted trough. The base of this feature will reach the Four Corners
Monday morning before continuing to eject into the Central Plains,
and the overlap of height falls with an amplifying jet streak will
produce large scale ascent across the Central Rockies and Four
Corners today. Available moisture is somewhat scarce (PWs only
around 0.25" and around the 10th percentile according to NAEFS) but
the impressive, albeit transient, deep layer lift will overcome
that to produce a swath of heavy snowfall. Snow should begin across
the Great Basin this morning, but intensify in response to better
lift aided by upslope flow over the Wasatch/Uintas this afternoon,
and then the CO Rockies/San Juans/Sangre de Cristos this evening
and tonight. Snow should end early Monday morning. WPC=20
probabilities suggest a high risk (>80% chance) of more than 6=20
inches across most of these mountain ranges, with snow levels=20
generally 4000-5000 ft.



...Central Plains & Ozarks through the Northeast...
Days 2-3...

...Widespread impactful snow and ice likely, but uncertainty with
respect to timing and track remains...

A complex evolution of mid-level features will create the first
widespread winter precipitation event from the Ohio Valley into the Appalachians, Mid-Atlantic, and Northeast. However, uncertainty
remains considerable at this time range and model guidance
continues to feature a variety of solutions which will affect the
accompanying impacts.

This system will develop initially in response to a shortwave
diving out of the Central Rockies Monday afternoon, and this
feature is expected to become neutrally tilted as vorticity lobes
swing through its base by the time it reaches the Ohio Valley
Tuesday morning. Thereafter, the shortwave tracks rapidly east
while maintaining its modest amplitude, exiting New England by 12Z
Wednesday. The global guidance has come into much better agreement
this morning with the progged evolution, maintaining a flatter and
faster wave, and in general, this upper pattern does not=20
conceptually support a widespread significant snowfall.=20

However, there are caveats that may make this a bit more=20
impressive than it would otherwise appear at 500mb. This is=20
primarily due to the amplification and phasing of upper jet=20
streaks: one amplifying downstream of the shortwave and a second=20
subtropical jet streak emerging from Mexico. The interaction of
this jet energy is progged to occur across the Mid-Mississippi
Valley Monday night, with the strengthening result then arcing
poleward through Tuesday to provide more impressive lift both
through the RRQ and LFQ. The strengthening jet streak will provide
sufficient upper ventilation, in conjunction with the mid-level
height falls, to produce surface cyclogenesis along the Gulf Coast
Tuesday morning, with this low then deepening as it tracks rapidly
northeast to off the coast of the Carolinas and then towards the
40/70N benchmark. The SLP trends of the various ensemble camps=20
have been for a faster solution with also some latitudinal gain,=20
suggesting this will not be a heavy snow event for the I-95=20
corridor, which is supported by an unfavorable surface high=20
position as well, but could still cause impactful wintry=20
precipitation across a large area.

As the synoptics intensify and the surface low moves east,
increasing WAA on a 30-50 kts 850mb LLJ will spread northward
leading to an expansion of precipitation. Where this interacts with
the strengthening jet streak, a stripe of heavy banded
precipitation is likely, which will fall as snow in many areas.=20

The first band is expected Monday into Monday night from the=20
Central Plains through the Ohio Valley where the ageostrophic=20
response to the LFQ of the upper jet will help intensify 700-600mb=20
fgen, crossing directly the deepening DGZ (SREF DGZ 50mb depth=20
probabilities > 50%). This should produce a stripe of heavy snow
rates from KS through the Ohio Valley, and although the band will
be progressive, WPC probabilities indicate a moderate risk (50-70%
chance) for at least 2 inches from central KS through eastern OH,
with locally higher amounts of 4+ inches possible (10-30%) aided by
fluffy SLRs. South of this band, increasing moist isentropic=20
ascent atop the retreating cold air will result in an axis of=20
freezing rain across the Ozarks where WPC probabilities are modest
(10-30%) for at least 0.1" of ice accretion, highest in central AR.

Then, during D3 /12Z Tue to 12Z Wed/ the moist isentropic ascent
maximizes leading to widespread heavy precipitation along and ahead
of the strengthening low pressure system. With the surface high
retreating and a lack of mid-level confluence to lock in cold air,
many areas of the Mid-Atlantic into the Northeast will begin as a
brief period of mixed precip, but should quickly change to rain
Tuesday morning, especially along and east of I-95. Inland,
however, the strong WAA, especially in the 850-700mb layer, will=20
result in front end heavy snow, most likely from Kentucky northeast
into interior New England. There is still uncertainty into how far
north the warm air will spread to cause changeover, but=20
significant snow accumulations are likely as reflected by WPC
probabilities that have increased, and now suggest a greater than
70% chance for 4+ inches of snow from the Poconos through Downeast
Maine. Locally more than 8 inches is possible, most likely in the
higher terrain of central New England. It is prudent to note that=20
while most of the guidance does not support an I-95 snow event, the
ECMWF AIFS ensemble, and even to some degree the EFI, suggest some
heavier snow farther south than most of the other camps, which=20
could bring more impactful weather to I-95 and is worth continuing=20
to monitor.

Finally, south of the heavy snow and across the terrain of the
Southern and Central Appalachians, a period of light to moderate
freezing rain is likely which could cause impactful ice
accretions, especially in the higher terrain. Current WPC
probabilities are as high as 30-50% for 0.1" of ice, with local
amounts approaching 0.25" possible in the vicinity of the Blue
Ridge of NC and VA.

Key Messages remain in effect for this system and are linked below
(Key Message #3)


Weiss


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_3.png__;!!DZ3fjg!_c96Fsm1kuyRpsYRqexGYrwZpDlGi30W0sU9cwbGm13v6= 4qFD27sEGEjMb_FSIQmd90IuTeJ7bqYRbSGk1Vc1yHTKf4$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 302021
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
321 PM EST Sun Nov 30 2025

Valid 00Z Mon Dec 01 2025 - 00Z Thu Dec 04 2025


...Great Lakes to the Interior Northeast...
Day 1...

The storm system responsible for the heavy and disruptive snowfall
that blanketed the Midwest and Great Lakes is tracking into Ontario
this afternoon. Cyclonic flow and CAA within WNW-NW winds will
reinvigorate the LES machine across the Upper Great Lakes, snow
belts of western MI and northern IN, and typical snow belts to the
east of Lakes Erie and Ontario. Snow bands will be capable of
producing anywhere between 1-2"/hr snowfall rates due to the
favorably unstable low-level profiles and a pivoting 850-700mb
trough over head this evening. WPC probabilities show moderate
chance probabilities (40-60%) for additional snowfall totals >4"=20
over far northwest PA and across the Tug Hill. An additional 1-4"
of snow is forecast in the Green and White Mountains before
tapering off by early Monday morning.


...Central Rockies/Central Plains/Mid-South/OH Valley...
Days 1-2...

A 500mb positiviely-tilted trough is tracking through UT today and
will head for the CO/NM Rockies by early Monday morning. The
combination of height falls with a strengthening jet streak will=20
produce large scale ascent across the Central Rockies and Four=20
Corners today and into tonight. Heavy snowfall will be primarily
confined to the >10,000ft peaks of the CO/NM Rockies, although some minor-to-moderate accumulations between 7,000-10,000ft are
possible.=20

As the upper trough tracks east towards the Central Plains tonight,
healthy 500mb PVA coupled with a strengthening 250mb jet streak
will foster healthy synoptic-scale divergence aloft. Guidance also
shows a strengthening 850-700mb WAA regime and corresponding 290K
isentropic ascent over the Central Plains that is likely to result
in a band of moderate-to-heavy snow tracking from northern KS early
Monday morning and across the heart of the Midwest by Monday
afternoon. Temperatures are cold enough aloft to support fluffy
SLRs (>15:1 in most cases) and it is progressive. WPC probabilities
show most accumulations will range between 1-4", given WPC
probabilities for >4" are low (10-30% at most in northeast
KS/northwest MO). However, there are some guidance members that
depict some localized totals >4" by the time the band of snow exits
to the east Monday evening. The same mechanism producing snow in=20
the Central Plains heads for the OH Valley and western PA. Snowfall accumulations will generally range between 1-4" through Tuesday=20
morning.=20

Farther south, as low-level WAA and Gulf moisture spreads over and
air-mass that features sub-freezing temperatures and dry
dewpoints, freezing rain is expected to unfold from the
ArkLaTex eastward across central and southern AR and into western
TN. the plume of low-level moisture does not last long, but 290K
isentropic ascent sticks around long enough for some disruptive=20
ice accumulations in these areas on Monday. WPC probabilities show=20
low chances (10-30%) for ice accumulations than one-tenth of an=20
inch, but there are moderate chances (40-60%) for ice=20
accumulations over one-hundreth in central AR. The WSSI shows a=20
large swath of Minor Impacts across central AR and as far north as=20
the MO/AR border, but some localized Moderate Impacts in central AR
are possible.=20


...Central Appalachians & Northeast...
Days 2-3...

...Widespread hazardous snow and ice to blanket portions of the
Mid-Atlantic and Northeast Monday night and through Tuesday...

By Monday evening, the 500mb trough producing periods of snow over
the OH Valley will track across the Middle MS Valley Monday night
with a secondary disturbance tracking south of it towards the
Southeast. As a third disturbance approaches from the Great Lakes,
a strengthening 250mb jet streak over the Northeast will work with
a second 250mb jet streak over the South to creating a classic
"coupling jet streak" setup off the Mid-Atlantic coast. This will
be the basis for a strengthening winter storm that tracks initially
through the Southeast Monday night and up the East Coast by Tuesday
afternoon.

The primary ingredients are generally agreed upon on all guidance,
although how they come together and where the storm tracks is=20
still coming into focus. High pressure over the Northeast will=20
initially provide a sufficiently cold air-mass to support wintry=20 precipitation at the onset from the Central Appalachians on north=20
and east, but it will be exiting off Atlantic Canada on Tuesday. As
925-700mb WAA advances north Monday night and into Tuesday, any=20
initial snow over the Central Appalachians will changeover to a=20 sleet/freezing rain mix, then all freezing rain. Cold air damming=20
(CAD) will linger long enough in the higher terrain to support=20
disruptive ice accumulations that result in slick travel conditions
Monday night and into Tuesday morning. WPC probabilities show >50%
chances for ice accumulations over a tenth of an inch from the=20
Blue Ridge of western NC on north through the mountains of western=20
VA and eastern WV. There are some low-chance probabilities (10-30%)
for over a quarter inch of ice from VA's Skyline Drive on south and west
to the WV/VA border. The latest WSSI does depict Minor to Moderate
Impacts in these regions with a focus on treacherous travel=20
conditions.

Farther north over the Mid-Atlantic, precipitation is likely to
start out as snow over northern VA/MD, southern PA, and on north
towards the NYC metro Tuesday morning. Guidance then begins to
disagree on the handling of the transition and northward expansion
of the snow-wintry mix area. Low-level SErly flow is strong enough
to where most areas along I-95 should flip over to plain rain on
Thursday morning, but farther inland over the Piedmont of VA,
northern MD, and Lower Susquehanna Valley, low-lvel cold may stick
around long enough for a wintry mix to hang around longer. This is
likely to be the region's first accumulating snowfall, so there are
likely to detrimental impacts to travel even if snowfall and ice
accumulations are minor (1-3" of snow for these areas, up to a=20
tenth of an inch of ice in western MD and northwest VA). However,=20
from the Lehigh Valley and Poconos on north and east through=20
northwest NJ, the Catskills, and into interior southern New=20
England, snow is likely to remain the primary precip type.

The storm by Tuesday afternoon will begin to develop a closed lower
over the Delaware Valley that deepens south of Long Island by
Tuesday evening. To the north and east of the 850mb low, a
consolidated 850-700mb FGEN area will develop and result in a band
of heavy snow somewhere from northeast PA and southern NY (north of
NYC) through southern New England. Snowfall rates within this band
are likely to at least top 1"/hr. There still remains some
uncertainty on where this band sets up, but probabilistic guidance
is showing increase odds on a snowfall swath of >6" from the
Poconos and Catskills on north and east. The higher terrain across
New England (Berkshires, Worcester Hills, Green, Whites, Downeast
Maine) are the most favored for locally heavy snowfall as WPC=20
probabilities shows low-to-moderate chances (30-50%) for over 12"=20
in some spots. The latest WSSI does depict Moderate Impacts due to
snow from western MA and northern CT to southern NH and southern=20
ME with locally Major Impacts possible.=20

In summary, this is going to be the first accumulating snow of the
season for many areas from southern PA to areas just west of I-95,
potentially including the Boston metro area should more southern
guidance come to fruition. Expect travel delays on Tuesday and into
Tuesday night in affected areas. High pressure and dry conditions
return to the Northeast by early Wednesday morning.=20

Key Messages remain in effect for this system and are linked below
(Key Message #3)


Mullinax


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_3.png__;!!DZ3fjg!8j1a6fpP7PIestX6LxHG47zf9CWUftnDL_uYhqq5y-hZB= QnAJRuMy4jSvIskYFi6EXdf5gXbLAYOTj_7E-hkDpvbjsY$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 302029
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 PM EST Sun Nov 30 2025

Valid 00Z Mon Dec 01 2025 - 00Z Thu Dec 04 2025


...Great Lakes to the Interior Northeast...
Day 1...

The storm system responsible for the heavy and disruptive snowfall
that blanketed the Midwest and Great Lakes is tracking into Ontario
this afternoon. Cyclonic flow and CAA within WNW-NW winds will
reinvigorate the LES machine across the Upper Great Lakes, snow
belts of western MI and northern IN, and typical snow belts to the
east of Lakes Erie and Ontario. Snow bands will be capable of
producing anywhere between 1-2"/hr snowfall rates due to the
favorably unstable low-level profiles and a pivoting 850-700mb
trough over head this evening. WPC probabilities show moderate
chance probabilities (40-60%) for additional snowfall totals >4"=20
over far northwest PA and across the Tug Hill. An additional 1-4"
of snow is forecast in the Green and White Mountains before
tapering off by early Monday morning.


...Central Rockies/Central Plains/Mid-South/OH Valley...
Days 1-2...

A 500mb positiviely-tilted trough is tracking through UT today and
will head for the CO/NM Rockies by early Monday morning. The
combination of height falls with a strengthening jet streak will=20
produce large scale ascent across the Central Rockies and Four=20
Corners today and into tonight. Heavy snowfall will be primarily
confined to the >10,000ft peaks of the CO/NM Rockies, although some minor-to-moderate accumulations between 7,000-10,000ft are
possible.=20

As the upper trough tracks east towards the Central Plains tonight,
healthy 500mb PVA coupled with a strengthening 250mb jet streak
will foster healthy synoptic-scale divergence aloft. Guidance also
shows a strengthening 850-700mb WAA regime and corresponding 290K
isentropic ascent over the Central Plains that is likely to result
in a band of moderate-to-heavy snow tracking from northern KS early
Monday morning and across the heart of the Midwest by Monday
afternoon. Temperatures are cold enough aloft to support fluffy
SLRs (>15:1 in most cases) and it is progressive. WPC probabilities
show most accumulations will range between 1-4", given WPC
probabilities for >4" are low (10-30% at most in northeast
KS/northwest MO). However, there are some guidance members that
depict some localized totals >4" by the time the band of snow exits
to the east Monday evening. The same mechanism producing snow in=20
the Central Plains heads for the OH Valley and western PA. Snowfall accumulations will generally range between 1-4" through Tuesday=20
morning.=20

Farther south, as low-level WAA and Gulf moisture spreads over and
air-mass that features sub-freezing temperatures and dry
dewpoints, freezing rain is expected to unfold from the
ArkLaTex eastward across central and southern AR and into western
TN. the plume of low-level moisture does not last long, but 290K
isentropic ascent sticks around long enough for some disruptive=20
ice accumulations in these areas on Monday. WPC probabilities show=20
low chances (10-30%) for ice accumulations than one-tenth of an=20
inch, but there are moderate chances (40-60%) for ice=20
accumulations over one-hundreth in central AR. The WSSI shows a=20
large swath of Minor Impacts across central AR and as far north as=20
the MO/AR border, but some localized Moderate Impacts in central AR
are possible.=20


...Central Appalachians & Northeast...
Days 2-3...

...Widespread hazardous snow and ice to blanket portions of the
Mid-Atlantic and Northeast Monday night and through Tuesday...

By Monday evening, the 500mb trough producing periods of snow over
the OH Valley will track across the Middle MS Valley Monday night
with a secondary disturbance tracking south of it towards the
Southeast. As a third disturbance approaches from the Great Lakes,
a strengthening 250mb jet streak over the Northeast will work with
a second 250mb jet streak over the South to creating a classic
"coupling jet streak" setup off the Mid-Atlantic coast. This will
be the basis for a strengthening winter storm that tracks initially
through the Southeast Monday night and up the East Coast by Tuesday
afternoon.

The primary ingredients are generally agreed upon on all guidance,
although how they come together and where the storm tracks is=20
still coming into focus. High pressure over the Northeast will=20
initially provide a sufficiently cold air-mass to support wintry=20 precipitation at the onset from the Central Appalachians on north=20
and east, but it will be exiting off Atlantic Canada on Tuesday. As
925-700mb WAA advances north Monday night and into Tuesday, any=20
initial snow over the Central Appalachians will changeover to a=20 sleet/freezing rain mix, then all freezing rain. Cold air damming=20
(CAD) will linger long enough in the higher terrain to support=20
disruptive ice accumulations that result in slick travel conditions
Monday night and into Tuesday morning. WPC probabilities show >50%
chances for ice accumulations over a tenth of an inch from the=20
Blue Ridge of western NC on north through the mountains of western=20
VA and eastern WV. There are some low-chance probabilities (10-30%)
for over a quarter inch of ice from VA's Skyline Drive on south and west
to the WV/VA border. The latest WSSI does depict Minor to Moderate
Impacts in these regions with a focus on treacherous travel=20
conditions.

Farther north over the Mid-Atlantic, precipitation is likely to
start out as snow over northern VA/MD, southern PA, and on north
towards the NYC metro Tuesday morning. Guidance then begins to
disagree on the handling of the transition and northward expansion
of the snow-wintry mix area. Low-level SErly flow is strong enough
to where most areas along I-95 should flip over to plain rain on
Thursday morning, but farther inland over the Piedmont of VA,
northern MD, and Lower Susquehanna Valley, low-lvel cold may stick
around long enough for a wintry mix to hang around longer. This is
likely to be the region's first accumulating snowfall, so there are
likely to detrimental impacts to travel even if snowfall and ice
accumulations are minor (1-3" of snow for these areas, up to a=20
tenth of an inch of ice in western MD and northwest VA). However,=20
from the Lehigh Valley and Poconos on north and east through=20
northwest NJ, the Catskills, and into interior southern New=20
England, snow is likely to remain the primary precip type.

The storm by Tuesday afternoon will begin to develop a closed lower
over the Delaware Valley that deepens south of Long Island by
Tuesday evening. To the north and east of the 850mb low, a
consolidated 850-700mb FGEN area will develop and result in a band
of heavy snow somewhere from northeast PA and southern NY (north of
NYC) through southern New England. Snowfall rates within this band
are likely to at least top 1"/hr. There still remains some
uncertainty on where this band sets up, but probabilistic guidance
is showing increase odds on a snowfall swath of >6" from the
Poconos and Catskills on north and east. The higher terrain across
New England (Berkshires, Worcester Hills, Green, Whites, Downeast
Maine) are the most favored for locally heavy snowfall as WPC=20
probabilities shows low-to-moderate chances (30-50%) for over 12"=20
in some spots. The latest WSSI does depict Moderate Impacts due to
snow from western MA and northern CT to southern NH and southern=20
ME with locally Major Impacts possible.=20

In summary, this is going to be the first accumulating snow of the
season for many areas from southern PA to areas just west of I-95,
potentially including the Boston metro area should more southern
guidance come to fruition. Expect travel delays on Tuesday and into
Tuesday night in affected areas. High pressure and dry conditions
return to the Northeast by early Wednesday morning.=20

Key Messages remain in effect for this system and are linked below
(Key Message #3)


Mullinax



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_3.png__;!!DZ3fjg!4a3u3xvT3-hHMgEuVV19WxvIhLYs9AwNztPM6v7_Rvx-N= fA7rqvdw0CdltnXbH7K29K2qwndPvJ_PXi1VPNvhwlFOkk$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 010804
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
304 AM EST Mon Dec 1 2025

Valid 12Z Mon Dec 01 2025 - 12Z Thu Dec 04 2025


...Central Plains through the Mid-Atlantic & Northeast...=20
Days 1-3...

...Widespread moderate to heavy snow from the Central Plains to the
Northeast will impact travel early this week while treacherous
icing occurs across the Appalachians...

A potent but positively tilted mid-level shortwave trough will be
advancing eastward from the Four Corners to start the period /12Z
today/ and move progressively eastward into the Ohio Valley by
Tuesday morning. During this translation, the feature, while
remaining of modest amplitude, may take on at least a neutral tilt
as vorticity continues to swing through the base of the
accompanying parent trough, and the entire system should be off the
New England Coast by 12Z Wednesday with only subtle amplification
expected. Although this shortwave will remain modest overall, the
accompanying jet streaks, both a downstream intensifying feature
and the broader subtropical jet lifting out of Mexico, are expected
to phase across the southern/central Plains today. The increasing
ascent left by the resulting RRQ overlapping height falls from the
shortwave will result in surface cyclogenesis along the Gulf Coast
tonight. This surface low is then expected to track rapidly
northeast across the southern Mid-Atlantic states and then deepen
just inside the 40N/70W Benchmark Tuesday night before lifting into
into the Canadian Maritimes.

This evolution will result in widespread snow and freezing rain
across the eastern half of the country, with two distinct areas of
impactful wintry precipitation.

On the north side of this system, a swath of moderate snow is
expected on D1 from Kansas through the Ohio Valley. This is in
response to the strengthening/phased jet streak which will begin to
tilt poleward to support impressive upper diffluence. At the same
time, some mid-level frontogenesis will be intensified by this jet
streak, forcing favorable overlap of ascent into the deepening DGZ
(SREF probabilities for 100mb of depth over 30% now) which will
support heavy snowfall rates within a translating band of 1"/hr or
more at times, aided by fluffy SLRs. The guidance has trended=20
upward with this feature, and WPC probabilities indicate a 10-30%
chance for at least 4 inches of snow from near Kansas City through
just south of Chicago.


As this band moves east into the Ohio Valley, it will become=20
merged with the larger system developing near the Gulf as=20
impressive moist isentropic ascent begins and lifts a theta-e ridge
northward to expand the precipitation shield. The strong 850mb WAA
will provide additional ascent, with the accompanying fgen serving
to intensify omega into the DGZ. While the WAA will likely result=20
in a burst of moderate snowfall in many areas from the Mid-
Atlantic/Ohio Valley northeast, a lack of resupplying cold air as=20
the surface high retreats will enable a quick transition to=20
mixed/rain, especially along and east of I-95 between VA and MA.=20
However, NW of the I-95 corridor, a prolonged period of moderate to
at times heavy snow is likely, with 1+"/hr rates spreading from PA
to ME. This will create an axis of snowfall for which WPC=20
probabilities indicate a high risk (>70% chance) for 4+ inches from
the Poconos through Downeast Maine, with locally as much as 8-12=20
inches possible (50% chance) from the Berkshires through the=20
Monadnock region of NH and into southern ME.

It is important to add as well, that despite what should be a
relatively quick transition from snow to mix to rain along I-95,
the Tuesday morning commute could be significantly impacted.

South of the heavy snow axes, two areas of impactful freezing rain
are also anticipated. The first will be across portions of
AR/MO/KY, in the vicinity of the Ozarks on Monday morning as
isentropic ascent and the accompanying moisture plume spread
precipitation into this region. Initially, surface wet-bulb
temperatures will be sub-freezing, so precipitation will fall as
freezing rain in response to the warm nose pivoting overhead.
However, this p-type should generally be short lived except in the
coldest regions, and WPC probabilities for 0.1" of ice peak around
30% in central AR.

More significant icing is likely across portions of the central and
southern Appalachians as isentropic ascent and accompanying WAA
intensify Monday night into Tuesday. Here, wet-bulb temperatures
will again be below freezing leading to an extended period of
freezing rain from SW NC into western MD. Although the high
retreats, this cold air may be more challenging to scour out,
especially in the higher elevations, leading to an extended period
of freezing rain with impactful ice accretions likely. WPC
probabilities D1 into D2 suggest a high risk (>70%) for at least
0.1" of icing from western NC through the Shenandoah region of VA,
with a low chance (10-30%) of up to 0.25" in isolated locations.

Key Messages remain in effect for this system and are linked below
(Key Message #3)


...Northern to Southern Rockies...=20
Days 2-3...

A shortwave digging out of British Columbia embedded within broad
cyclonic flow across the eastern half of the CONUS will spread
increasing synoptic ascent across the Intermountain West beginning
Tuesday morning. This shortwave will move progressively southeast
Tuesday, and may become more amplified despite maintaining a strong
positive tilt by Wednesday morning in response to secondary
vorticity maxima digging through its base. This will result in a
slowing and amplification of the trough, with downstream ascent
maximizing through height falls, PVA, and downstream intensifying
jet energy.=20

Available moisture will generally be modest as reflected by near-
normal PW anomalies, but the overlapped synoptic lift will be more
than sufficient to wring this out as periods of moderate to heavy
snowfall across much of the terrain. At the same time, a wave of
low pressure is progged to drop southeast coincident with the
shortwave trough, and a secondary front will also push south out of
Canada to cool the column while additionally leading to localized
upslope flow. Despite a shallow DGZ noted in regional forecast
soundings, the best ascent may maximize within this snow growth
region to enhance snowfall, and this suggests a broad swath of
moderate snow is likely Tuesday and Wednesday across much of the
Rockies.

WPC probabilities for 4+ inches D2 are highest from MT through WY,
with local maxima in snowfall above 8 inches possible across the
Little Belts and Absarokas, with snow levels running around
2000-3000 ft. By D3, the heaviest snow pivots southeast reaching
the CO Rockies, the San Juans, and Sangre de Cristos, where WPC
probabilities indicate a moderate risk (50-70%) for 6+ inches of
snowfall. Snow levels continue to fall on Wednesday as well such
that even the I-25 urban corridor from Cheyenne to Santa Fe may
experience a few inches of snow, with the higher accumulations
expected across the Raton Mesa and Palmer Divide.


...Great Lakes & Northeast...
Day 3...

A strong arctic front will race across the Great Lakes Wednesday,
likely reaching Upstate NY by Thursday morning before continuing
into New England beyond this forecast period. While confidence is
low at this time, the signals appear favorable for snow squalls
along this front as it dives southeast. The trends in the GFS SnSq
parameter have decayed a bit in recent runs, but the environment at
this time frame appears at least marginally favorable for a line,
or lines, of convective snow showers/snow squalls Wednesday into
Thursday. While snowfall amounts will be minimal, snow squalls can
cause dangerous driving due to briefly heavy snow rates and gusty
winds, so this event will need to be monitored as it gets closer.


Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_3.png__;!!DZ3fjg!5yQB3jpQNoHGi7CLwb89D4XfQqfQD6y2WYs0GA0deyuOX= 5XM7r-Hwq9HUl0fa45gZku1edttTkTaRH-BsCW62nKKERs$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 012030
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
330 PM EST Mon Dec 1 2025

Valid 00Z Tue Dec 02 2025 - 00Z Fri Dec 05 2025


...Central Plains through the Mid-Atlantic & Northeast...=20
Days 1-2...

...Widespread moderate to heavy snow from the Central Plains to the
Northeast will impact travel early this week while treacherous
icing occurs across the Appalachians...

A positively-tilted upper trough will continue to move steadily
east of the Rockies, assuming a neutral tilt, with phasing streams
over the Plains early in the period. This trough will continue to=20
move east across the Midwest on Tuesday, reaching the East Coast=20
late in the day, before becoming negatively-tilted as it moves off=20
of the Mid Atlantic/Northeast coasts Tuesday night.=20

At the surface, low pressure will develop over the northern Gulf=20
tonight before energy transfers to low pressure along the=20
Southeast coast. Supported by a coupled upper jet, this low will=20
deepen quickly as it tracks north along the Mid Atlantic to the=20
Northeast coast on Tuesday. With the 12Z ECMWF now shifted north,=20
the general consensus of the deterministic runs and the ensemble=20
means show the low tracking near the 40N/70W benchmark around 00Z=20
Wednesday before continuing on a track east of the Canadian=20
Maritimes Wednesday morning.

Upper level forcing along with low-to-mid level frontogenesis will
continue to support light to moderate snow spreading east from the
mid Mississippi through the Ohio valleys tonight, with the latest=20
WPC probabilities indicating that accumulations for most areas will
remain under 4 inches.

As this band moves east into the Ohio Valley, it will merge with=20
the larger system developing near the Gulf as impressive moist=20
isentropic ascent supports a north-moving theta-e ridge and an=20
expanding precipitation shield. Strong 850mb WAA will provide=20
additional ascent, with the accompanying frontogenesis serving to=20
intensify omega into the DGZ. While the WAA will likely result in a
burst of moderate snowfall in many areas across the interior Mid=20
Atlantic into the Northeast, a lack of resupplying cold air as a=20
surface high to the north retreats will enable a quick transition=20
to mixed/rain, especially along and east of the I-95 corridor from
northern Virginia to Boston. The 12Z models trended slightly=20
warmer, further indicating that areas from DC to NYC will be=20
mostly, if not entirely, all rain. However, northwest of the I-95=20
corridor, the story remains much different, where a prolonged=20
period of moderate, to at times heavy snow, is likely, with 1+"/hr=20
rates spreading from Pennsylvania to Maine. This will create an=20
axis of snowfall for which WPC probabilities continue to show a=20
high risk (>70% chance) for 4+ inches from the Poconos through=20
Downeast Maine, with locally as much as 8-12 inches possible (50%=20
chance) across parts of the Catskills and from the Berkshires to=20
southern Maine, including the northern Worcester Hills and=20
Monadnock region.

South of the heavy snow axes, light ice accumulations will shift
northeast from southern Arkansas into eastern Tennessee and=20
Kentucky. WPC probabilities indicate that where ice does
accumulate it will remain under 0.10 inch for most areas.

Meanwhile, more significant icing is likely to develop starting=20
tonight across portions of the central and southern Appalachians as
isentropic ascent and accompanying WAA intensify. Subfreezing wet-
bulb temperatures will support an extended period of freezing rain
along the southern to central Appalachians from North Carolina to=20
western Maryland. Although the high to the north will be=20
retreating, this cold air may be more difficult to scour out,=20
especially in the more sheltered locations, leading to an extended=20
period of freezing rain with impactful ice accretions likely. WPC=20 probabilities show 50 percent or greater probabilities for at least
0.1 inch of ice from across parts of western North Carolina=20
northward along the southern Blue Ridge into southern West Virginia
and the Shenandoah region of Virginia, with a low chance (10-30%)=20
of up to 0.25 inch in isolated locations.

Key Messages remain in effect for this system and are linked below
(Key Message #3)


...Northern to Southern Rockies...=20
Days 1-3...

A shortwave will dig south out of British Columbia into the
northwestern U.S. overnight. This shortwave will continue to move=20
southeast Tuesday into Wednesday, and may become more amplified as
it drops through the Great Basin in response to secondary=20
vorticity maxima digging through its base. This will result in a=20
slowing and amplification of the trough, with downstream ascent=20
maximizing through height falls, PVA, and downstream intensifying=20
jet energy.=20

Available moisture will generally be modest as reflected by near-
normal PW anomalies, but the overlapped synoptic lift will be more
than sufficient to wring this out as periods of moderate to heavy
snowfall across much of the terrain. At the same time, a wave of
low pressure is progged to drop southeast coincident with the
shortwave trough, and a secondary front will also push south out of
Canada to cool the column while additionally leading to localized
upslope flow. Despite a shallow DGZ noted in regional forecast
soundings, the best ascent may maximize within this snow growth
region to enhance snowfall, and this suggests a broad swath of
moderate snow is likely Tuesday and Wednesday across much of the
Rockies.

WPC probabilities for 4+ inches Day 1 are highest from northwestern
Montana to northwestern Wyoming and northern Idaho, with local=20
maxima in snowfall above 8 inches possible across the higher
terrain. By Day 2, the heaviest snow pivots southeast reaching the
central Rockies, notably the Colorado ranges, where most of the
higher probabilities for accumulations above 4 inches are=20
centered. The southern shift is expected to continue into Day 3,=20
with the Sangre de Cristos in northern New Mexico the focus for the
higher probabilities for amounts over 4 inches.

...Great Lakes & Northeast...
Day 3...

A strong arctic front will race across the Great Lakes Wednesday,
likely reaching Upstate NY by Thursday morning before continuing
into New England. The signals appear favorable for snow squalls=20
along this front as it dives southeast. The trends in the GFS SnSq=20
parameter remain fairly muted, however the NAM ramps up notably
across parts of Pennsylvania and Upstate NY into New England on
Thursday. While snowfall accumulations will be minimal, snow=20
squalls can cause dangerous driving due to briefly heavy snow rates
and gusty winds, so this event will need to be monitored as it=20
gets closer.

Pereira/Weiss

...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_3.png__;!!DZ3fjg!6oXhXucCqMO6rFQZw4LhD3-riI-5FAbKI4WO1sf2hP8LT= oEz6p5IVVzBv2VrbH0G1tj2lmGYpsUo2RcvZ2Kbm3cNMKo$=20


$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 020730
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
230 AM EST Tue Dec 2 2025

Valid 12Z Tue Dec 02 2025 - 12Z Fri Dec 05 2025


...Mid-Atlantic & Northeast...=20
Days 1...

...Rapidly deepening coastal low will bring heavy snow to the
interior Mid-Atlantic and Northeast today/tonight...

Low pressure will move off the NC/VA coast this morning and then
track rapidly northeast along the coast, passing inside the 40N/70W
benchmark before lifting into the Canadian Maritimes by Wednesday
morning. The overlap of height falls, a coupled jet streak, and the
latent heat release along the offshore baroclinic gradient will
allow the low to rapidly deepen during this period, spreading
heavy precipitation and gusty winds into the Northeast.

As the low moves up the coast, persistent and impressive moist
isentropic ascent will surge a theta-e ridge northward to support
expanding heavy precipitation. The coincident WAA at 850mb will
produce additional ascent, with intensifying fgen driving some
banded precipitation, but also warm the column aloft as the surface
high pressure retreats rapidly to the east. The guidance has
trended just a bit warmer again overnight, and while most areas
along I-95 and points west will likely start as a brief period of
snow/sleet, any meaningful accumulation is anticipated only well
inland and at higher elevations, especially in southern and central
New England. The big cities from Washington, D.C. to Boston, MA may
start as snow before changing over to rain (and Boston may change
back to snow briefly before the system exits Wednesday morning).
However, well NW, WPC probabilities are high (>70%) for at least 6
inches of snow from the Catskills through the Berkshires, the
Worcester Hills, and across much of southern NH and ME (away from
the immediate coast) where locally as much as 12 inches is possible
(10-30% chance).

Additionally, while most of the freezing rain accompanying this
system is expected to wane before 12Z/Tuesday, an additional 0.1"
of ice is possible (10-30% chance) across the Central Appalachians
in the vicinity of Shenandoah NP.

Key Messages remain in effect for this system and are linked below
(Key Message #3)


...Northern to Southern Rockies...=20
Days 1-2...

A shortwave digging south out of British Columbia into the=20
northwestern U.S. will be positioned across the interior Northwest
to begin the forecast period /12z Tuesday/. This shortwave will=20
continue to move southeast through Wednesday, and may become more=20
amplified as it drops through the Great Basin in response to=20
secondary vorticity maxima digging through its base. This will=20
result in a slowing and amplification of the trough, with=20
downstream ascent maximizing through height falls, PVA, and=20
downstream intensifying jet energy, especially as it approaches the
Four Corners Wednesday morning.

Available moisture will generally be modest as reflected by near-
normal PW anomalies, but the overlapped synoptic lift will be more
than sufficient to wring this out as periods of moderate to heavy
snowfall across much of the terrain. At the same time, a wave of
low pressure is progged to drop southeast coincident with the
shortwave trough, and a secondary front will also push south out of
Canada to cool the column while additionally leading to localized
upslope flow. Despite a shallow DGZ noted in regional forecast
soundings, the best ascent is progged to intersect within this=20
snow growth region to enhance snowfall, and this suggests a broad=20
swath of moderate snow is likely today and Wednesday across much=20
of the Rockies.

WPC probabilities D1 for 6+ inches are highest in the terrain above
5000 ft from the Salmon River/Sawtooth Range of ID through the
Absarokas, Little Belts, Tetons, and down into the Park Range and
other CO Rockies. During D2, the highest probabilities shift south
with the shortwave and increase, reaching above 80% for 6+ inches
along much of the Sangre de Cristos where locally 12+ inches is
likely. Additionally, as this shortwave digs south, some moderate
snowfall is likely along the I-25 urban corridor of Colorado,
bringing some notable snow to a region that has yet to experience
much so far this winter.

...Great Lakes & Northeast...
Day 3...

A strong arctic front will race across the Great Lakes Wednesday,
likely reaching Upstate NY by Thursday morning before continuing
into New England and crossing offshore into the Atlantic Thursday
night. Environmental signals continue to appear favorable for snow
squalls along this front as it dives southeast, and the GFS and NAM
SnSQ parameter have both increased tonight, especially from western
PA through northern New England where a significant overlap of
0-2km fgen and SBCAPE as high as 200 J/kg exists in a region of
elevated low-level RH. This suggests increasing confidence in
linear snow squalls, especially Thursday. While snowfall=20
accumulations from this event will likely be minimal, brief intense
snow rates combined with gusty winds may create dangerous travel=20
across parts of the northern Great Lakes and interior Northeast.

Weiss


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_3.png__;!!DZ3fjg!9CitJsY81sgfvgcKlG6ZrnnEIhWwB6pKIFXM58UDsWGWr= 9HKJE7T1O8YkkonalX1bNrkX6KvtEsUu9UtiQFpNXUEnak$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 022034
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
334 PM EST Tue Dec 2 2025

Valid 00Z Wed Dec 03 2025 - 00Z Sat Dec 06 2025


...Northeast...=20
Days 1...

Low pressure now moving north along the Mid Atlantic coast will
deepen rapidly through the evening as the associated shortwave
trough moves through the Northeast/Mid Atlantic, and assumes a
negative tilt as it moves offshore. This system will move quickly
overnight, tracking from near the 40N/70W benchmark at 00Z to east
of Nova Scotia by daybreak. The back edge of the associated=20
precipitation shield will move quickly to the east as well, with=20
snowfall ending for most areas apart from coastal northern New=20
England by tomorrow morning. Additional snowfall accumulations=20
after 00Z are expected to be light for most areas, with WPC=20
probabilities indicating the chance for accumulations greater than=20
4 inches are negligible for most areas, with some 10-30=20
probabilities confined to coastal Maine and southern New Hampshire.

...Northern to Southern Rockies...=20
Days 1-2...

A low amplitude shortwave trough dropping through the Pacific
Northwest today is forecast to amplify as it digs south along the=20
Sierra Nevada/Great Basin overnight, with the model consensus=20
showing a well-defined positively-tilted trough dropping into the=20 Southwest/Four Corners on Wednesday. Meanwhile at the surface, a cold
front will settle south into the southwestern U.S. A low level=20
circulation developing and dropping south through western Colorado=20
will help to enhance snowfall over the western Colorado ranges,=20
notably the San Juans, where WPC guidance shows some isolated=20
higher probabilities for accumulations greater than 6 inches on Day
1. More widespread higher amounts are expected to develop along=20
the eastern ranges from the Front Range south to the northern=20
Sangre de Cristos - supported by increasing upslope flow on the=20
backside of a sharp ridge nosing south along the High Plains.

=46rom Wednesday night into early Thursday, the shortwave over the
Southwest will begin to eject east, focusing snow further south
over the Rockies. Amounts are expected to me mostly light, with WPC probabilities indicating amounts over 6 inches will remain mostly
confined to the higher peaks of the southern Sangre de Cristos.


...Great Lakes & Northeast...
Days 1-3...

An arctic front associated with an amplifying trough over eastern=20
Canada will sweep across the upper Great Lakes on Wednesday,
setting off a period of lake effect snow showers that will continue
into early Thursday before a shortwave ridge moves over the region.
Overall, accumulations for the two-day period are expected to be=20
generally light. Although some parts of the eastern U.P. are likely
to see totals over 4 inches.

Meanwhile, the previously noted front will advance east of the
lakes, moving across the Northeast on Thursday. While heavy
accumulations along the front are not expected, snow squalls remain
a concern, with the NAM continuing to show some notable Snow=20
Squall Parameter values as the front advances across Upstate New=20
York and New England. This indicates a brief period of intense=20
snowfall that is likely to reduce visibilities and impact travel.=20
Behind the front, lake effect snow showers will develop briefly off
of lakes Erie and Ontario Wednesday night into Thursday, with the=20
best chance for heavy accumulations centered over the Tug Hill=20
region.

The aforementioned shortwave ridging is forecast to develop ahead
of another shortwave that is expected to dive southeast across
central Canada on Thursday and amplify as it brushes the upper=20
Great Lakes Friday morning. Most of the better forcing and lake
enhancement is expected to remain north of the lakes; however some
lighter amounts are likely, especially over northern Michigan.=20


...Mid South to the Mid Atlantic...
Day 3...

The previously noted shortwave over the Southwest will move east of
the southern Rockies on Thursday, becoming less amplified as it
moves into a region of confluent upper flow. However it will
provide enough lift to spread some light precipitation north into
the Mid South/Tennessee Valley, with a low end chance for some=20
light wintry precipitation/ice accumulations Thursday night into=20
early Friday. A greater chance for light snow/ice accumulations is=20
expected to develop farther east over the southern Appalachians,=20
where a cold air wedge is forecast to linger long enough to support
at least some minor accumulations on Friday.=20

Pereira

...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_3.png__;!!DZ3fjg!5dX0zkdWbchHEQyfBkNAry9V7K3ebVmkRcD5w6GTZEdic= Rf4ygZ7kFSH-wJMsfxpoP2Zrn2TyshbLy4IoKDLGbL13OA$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 022051
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
351 PM EST Tue Dec 2 2025

Valid 00Z Wed Dec 03 2025 - 00Z Sat Dec 06 2025


...Northeast...=20
Days 1...

Low pressure now moving north along the Mid Atlantic coast will
deepen rapidly through the evening as the associated shortwave
trough moves through the Northeast/Mid Atlantic, and assumes a
negative tilt as it moves offshore. This system will move quickly
overnight, tracking from near the 40N/70W benchmark at 00Z to east
of Nova Scotia by daybreak. The back edge of the associated=20
precipitation shield will move quickly to the east as well, with=20
snowfall ending for most areas apart from coastal northern New=20
England by tomorrow morning. Additional snowfall accumulations=20
after 00Z are expected to be light for most areas, with WPC=20
probabilities indicating the chance for accumulations greater than=20
4 inches are negligible for most areas, with some 10-30=20
probabilities confined to coastal Maine and southern New Hampshire.

...Northern to Southern Rockies...=20
Days 1-2...

A low amplitude shortwave trough dropping through the Pacific
Northwest today is forecast to amplify as it digs south along the=20
Sierra Nevada/Great Basin overnight, with the model consensus=20
showing a well-defined positively-tilted trough dropping into the=20 Southwest/Four Corners on Wednesday. Meanwhile at the surface, a cold
front will settle south into the southwestern U.S. A low level=20
circulation developing and dropping south through western Colorado=20
will help to enhance snowfall over the western Colorado ranges,=20
notably the San Juans, where WPC guidance shows some isolated=20
higher probabilities for accumulations greater than 6 inches on Day
1. More widespread higher amounts are expected to develop along=20
the eastern ranges from the Front Range south to the northern=20
Sangre de Cristos - supported by increasing upslope flow on the=20
backside of a sharp ridge nosing south along the High Plains.

=46rom Wednesday night into early Thursday, the shortwave over the
Southwest will begin to eject east, focusing snow further south
over the Rockies. Amounts are expected to me mostly light, with WPC probabilities indicating amounts over 6 inches will remain mostly
confined to the higher peaks of the southern Sangre de Cristos.


...Great Lakes & Northeast...
Days 1-3...

An arctic front associated with an amplifying trough over eastern=20
Canada will sweep across the upper Great Lakes on Wednesday,
setting off a period of lake effect snow showers that will continue
into early Thursday before a shortwave ridge moves over the region.
Overall, accumulations for the two-day period are expected to be=20
generally light. Although some parts of the eastern U.P. are likely
to see totals over 4 inches.

Meanwhile, the previously noted front will advance east of the
lakes, moving across the Northeast on Thursday. While heavy
accumulations along the front are not expected, snow squalls remain
a concern, with the NAM continuing to show some notable Snow=20
Squall Parameter values as the front advances across Upstate New=20
York and New England. This indicates a brief period of intense=20
snowfall that is likely to reduce visibilities and impact travel.=20
Behind the front, lake effect snow showers will develop briefly off
of lakes Erie and Ontario Wednesday night into Thursday, with the=20
best chance for heavy accumulations centered over the Tug Hill=20
region.

The aforementioned shortwave ridging is forecast to develop ahead
of another shortwave that is expected to dive southeast across
central Canada on Thursday and amplify as it brushes the upper=20
Great Lakes Friday morning. Most of the better forcing and lake
enhancement is expected to remain north of the lakes; however some
lighter amounts are likely, especially over northern Michigan.=20


...Mid South to the Mid Atlantic...
Day 3...

The previously noted shortwave over the Southwest will move east of
the southern Rockies on Thursday, becoming less amplified as it
moves into a region of confluent upper flow. However it will
provide enough lift to spread some light precipitation north into
the Mid South/Tennessee Valley, with a low end chance for some=20
light wintry precipitation/ice accumulations Thursday night into=20
early Friday. A greater chance for light snow/ice accumulations is=20
expected to develop farther east over the southern Appalachians,=20
where a cold air wedge is forecast to linger long enough to support
at least some minor accumulations on Friday.=20

...Northern Rockies...
Day 3...

The next chance for heavy snowfall totals in the northern Rockies
will develop as a low amplitude shortwave slides off of the top of
the Pacific ridge into the region late Thursday into Friday.=20
Favorable mid to upper level forcing along with a notable influx of
Pacific moisture will be sufficient for some heavy totals over the
northern Rockies from northern Idaho and western Montana to=20
western Wyoming -- where WPC probabilities indicate widespread=20
totals over 4 inches are likely, with amounts over 8 inches=20
possible in the higher terrain.=20

Pereira

...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_3.png__;!!DZ3fjg!_o-SUQXPmGVKCQUA40WQkjG6mxm--y--ExzoWHd0zGwiZ= t3WKbKCcaAGBk-7uBOjIe-o6HDQyb7eerxWCf07fenphZ0$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 030755
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
255 AM EST Wed Dec 3 2025

Valid 12Z Wed Dec 03 2025 - 12Z Sat Dec 06 2025


...Southern/Central Rockies...
Days 1-2...

Shortwave which emerged from British Columbia Monday will continue
to track southeast across the Four Corners today while amplifying.
The guidance has trended a bit farther south and more amplified
with the evolution today, which should result in heavier snowfall
especially across the San Juans and Sangre de Cristos on D1.
Forcing for ascent downstream of this trough (in response to height
falls and modest divergence) will be enhanced by a strengthening
jet streak, especially tonight into Thursday morning, and periods
of impressive upslope flow as cold N/NE winds develop in advance of
an Canadian high pressure dropping into the Plains. Moisture within
the region is progged to be around to slightly below normal as
reflected by NAEFS ensembles, but the impressive overlapping ascent
will still maximize favorable to support heavy snow, especially
above 4000-5000 ft, with snow levels falling in conjunction with
waning snowfall intensity. WPC probabilities, especially across the
San Juans and Sangre de Cristos, have increased tonight, and now
feature a high risk (>70%) for more than 12 inches in the higher
terrain of these ranges. Into the lower terrain, WPC probabilities
indicate a moderate threat (30-50%) for at least 4" along the I-25
urban corridor, with locally more than 6" in the higher terrain of
the Raton Mesa and southern Palmer Divide.


...Great Lakes & Northeast...
Days 1-3...

Progressive flow across the Northeast will manifest in response to
a large gyre centered near Hudson Bay, which will shed periodic
shortwaves from the Great Lakes through the Northeast leading to
occasional enhanced ascent and lowered heights throughout. In
response to this evolution, the period will remain active through
LES and arctic fronts, and multiple rounds of snowfall, sometimes
heavy, are expected.

The first event will be associated with an arctic cold front
dragging southeast beneath a shortwave aloft. This front will
likely move rapidly across the Great Lakes today, and then across
the Northeast Thursday. Along and ahead of this front, the
environment continues to suggest an increasing threat for snow
squalls, especially across PA/NY and New England on Thursday. The
NAM SnSq parameter continues to be more aggressive than the GFS,
but the antecedent low-level environment ahead of the front appears
favorable for squall development. With 0-2km fgen maximizing along
the front into elevated RH and SBCAPE as high as 300 J/kg,
widespread linear squalls could result. Upstream into MI the threat
is not as high on D1, and although isolated squalls could occur,
the greater risk will be D2 in the Northeast. While total snowfall
will be minimal in any squall, rapidly changing conditions due to
heavy snow and gusty winds will create periods of dangerous travel
Thursday aftn. These squalls could become widespread, and after
coordination with the northeast WFOs, it is possible that with
future model cycles some enhanced messaging may be needed to
highlight the threat.

Behind this front, as well as behind a subsequent shortwave on
Friday, increased CAA will spread across the Great Lakes leading to
periods of lake effect snow (LES). The progressive flow will
support shortwave ridging between the two impulses, so the duration
of any LES with each shortwave/front should be somewhat limited.
However, 850mb temps falling to -15C to -20C Wednesday
night/Thursday, and then -10C to -15C late Friday, will create
steep lapse rates and deepening inversion depths to support bands
of heavy LES. The heaviest LES snowfall accumulations within the
LES bands are expected in the typical NW snow belts across the U.P.
of MI, the NW L.P. near Traverse City, and then along the
Chautauqua Ridge and into the Tug Hill Plateau. In these belts,
3-day snowfall of 6-12 inches is possible, highest across the U.P.


...Mid-South to the Mid-Atlantic...
Day 3...

Uncertainty abounds D3 with respect to a strung-out shortwave
exiting the Central Plains and becoming embedded within the more
zonal flow to the east. Although this shortwave is expected to be
of modest amplitude and fast moving, the accompanying upper jet is
progged to be powerful at over 150kts across the Mid-Atlantic,
leading to surface low pressure development across the Southeast.
This low will then race E/NE, producing a swath of at least light
wintry precipitation from the Tennessee Valley to the Mid-Atlantic
states.

There has been at least a modest northward shift/trend in the MSLP
fields from the various global ensembles the past few runs, and
while the ECMWF operational remains the most aggressive/north, that
solution cannot be ruled out. In fact, the trends in the 250mb jet
streak and from evaluation of the clusters (for which the primary
variance is the amplitude of the trough across the east) could
suggest a more subtle northward track of this low which would shift
more wintry precipitation into the area. It is still too early to
iron out these details, but at least a low-end risk for a few
inches of snow is possible as reflected by WPC probabilities which
reach 10-30% for 1+ inches of snow across the Central Appalachians
and into eastern VA/MD. This is notably lower than the recent NBM probabilities, and the trends continue to increase, so it is worth
watching the evolution of this event during the next few days.

South of the potential moderate snow, an axis of light freezing
rain is also possible where a p-type transition occurs. While the
location of the heaviest icing is also uncertain, current WPC
probabilities indicate a 10-30% chance for at least 0.1" of ice
across northern NC and into southern VA.


...Northern to Central Rockies...
Days 2-3...

The next chance for heavy snowfall totals in the northern Rockies
will develop as a low amplitude shortwave slides off of the top of
the Pacific ridge into the region late Thursday into Friday,
coincident with the LFQ of an impressive upper jet streak swinging
across the Northern Pacific. This will result in favorable mid to
upper level forcing along with a notable influx of Pacific
moisture, sufficient for some heavy totals , especially above
around 5000 ft as snow levels rise coincident with this moisture
plume moving into the area. Heavy snowfall accumulations are likely
D2 from the WA Cascades through the terrain of NW WY near
Yellowstone NP as reflected by WPC probabilities that suggest a
high risk (>70%) for 4+ inches, with impacts to many of the area
passes becoming likely.

Probabilities become even more impressive D3 across the higher
terrain from Glacier NP through Yellowstone NP including portions
of the Sawtooth/Salmon River ranges, Absarokas, terrain of NW WY,
and into the Park Range of CO. Here, WPC probabilities D3 reach
above 70% for 8+ inches, and D3 snowfall could be impressive above
generally 6000 ft where locally 1-2 feet is possible.

Weiss



$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 032015
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
315 PM EST Wed Dec 3 2025

Valid 00Z Thu Dec 04 2025 - 00Z Sun Dec 07 2025


...Southern/Central Rockies...=20
Day 1...

The sharp, positively-titled trough currently over the Four=20
Corners states will continue to translate eastward tonight before=20
ejecting into the central/southern Plains on Thursday. Forcing for=20
ascent downstream of this trough (in response to height falls and=20
modest divergence) will be enhanced by a strengthening jet streak,=20 especially tonight into Thursday morning. Meanwhile, Canadian high=20
pressure dropping into the Plains will result in impressive upslope
flow as cold N/NE winds develop in response. Moisture within the=20
region is progged to be around to slightly below normal as=20
reflected by NAEFS ensembles, but the impressive overlapping ascent
will still be favorable to support heavy snow. This will=20
especially be the case above 4000-5000 ft, with snow levels falling
in conjunction with waning snowfall intensity later tonight into=20
Thursday morning. The latest WPC probabilities continue to show=20
moderate to high chances (40-80%) for additional accumulations of=20

6 inches across portions of the southern San Juans and Sangre de=20

Cristo mountain ranges, with low to moderate chances (20-50%) of >8
inches.


...Great Lakes & Northeast...
Days 1-3...

Progressive flow across the Northeast will manifest in response to
a large gyre centered near Hudson Bay, which will shed periodic=20
shortwaves from the Great Lakes through the Northeast leading to=20
occasional enhanced ascent and lowered heights throughout. In=20
response to this evolution, multiple rounds of snowfall, sometimes=20
heavy, are expected through the period.=20

The first event will be associated with an arctic cold front=20
dragging southeast beneath a shortwave aloft. This front will move=20
rapidly across the eastern Great Lakes tonight, and then across the
Northeast on Thursday. Along and ahead of this front, the=20
environment continues to suggest an increasing threat for snow=20
squalls, especially across Upstate NY and New England on Thursday.=20
With 0-2km fgen maximizing along the front into elevated RH and=20
SBCAPE as high as 300 J/kg, widespread linear squalls are likely.=20
While total snowfall will be minimal in any squall, rapidly=20
changing conditions due to heavy snow and gusty winds will create=20
periods of dangerous travel Thursday afternoon and evening. As a=20
result, WPC has initiated Key Messages to highlight this event. See
the link below for more details.

Behind this front, as well as behind a subsequent shortwave on=20
Friday, increased CAA will spread across the Great Lakes leading to
periods of lake effect snow (LES). The progressive flow will=20
support shortwave ridging between the two impulses, so the duration
of any LES with each shortwave/front should be somewhat limited.=20
However, 850mb temps falling to between -15C to -20C Thursday, and=20
then between -10C to -15C late Friday into Saturday, will create=20
steep lapse rates and deepening inversion depths to support bands=20
of heavy LES. The heaviest LES snowfall accumulations within the=20
LES bands are expected in the typical NW snow belts across the U.P.
of MI, the NW L.P. near Traverse City, and then along the=20
Chautauqua Ridge and into the Tug Hill Plateau. In these belts,=20
3-day snowfall of 6-12 inches is possible, highest across the U.P.


...Mid-South to the Mid-Atlantic...=20
Day 2...

Plenty of uncertainty heading into Day 2 with respect to a strung-
out shortwave exiting the Central Plains and becoming embedded=20
within the more zonal flow to the east. Although this shortwave is=20
expected to be of modest amplitude and fast moving, the=20
accompanying upper jet is progged to be powerful at over 150kts=20
across the Mid-Atlantic, leading to surface low pressure=20
development across the Southeast. This low will then race E/NE,=20
producing a swath of at least light wintry precipitation from the=20
Tennessee Valley to the Mid-Atlantic states.=20

There has been at least a modest northward shift/trend in the=20
MSLP/QPF fields from the various global ensembles the past few=20
runs, with the ECMWF and various machine learning suites the=20
farthest north. While it still remains too early to iron out the=20
details, WPC probabilities of 1+ inches of snow across the Central=20 Appalachians and into eastern VA/MD have increased to 20-60%, with=20
the highest chances in the higher terrain of WV/VA. WPC=20
probabilities for 2+ inches are between 10-20% from eastern WV to=20
central VA.

South of the potential moderate snow, an axis of light
freezing rain is also possible where a p-type transition occurs
underneath a stubborn layer of low-level cold air. The latest WPC=20 probabilities maintain a 10-30% chance for at least 0.1" of ice=20
across northern NC and into southern VA.


...Northern to Central Rockies...=20
Days 1-3...

The next chance for heavy snowfall totals in the northern Rockies=20
will develop as a low amplitude shortwave slides off of the top of=20
the Pacific ridge into the region late Thursday into Friday,=20
coincident with the LFQ of an impressive upper jet streak swinging=20
across the Northern Pacific. This will result in favorable mid to=20
upper level forcing along with a notable influx of Pacific=20
moisture, sufficient for some heavy totals, especially above around
5000 ft as snow levels rise coincident with this moisture plume=20
moving into the area. Heavy snowfall accumulations are likely from=20
the WA Cascades through the terrain of NW WY near Yellowstone NP as
reflected by WPC probabilities that suggest a high risk (>70%) for
4+ inches, with impacts to many of the area passes becoming=20
likely.

Probabilities become even more impressive Day 2 and 3 across the=20
higher terrain from Glacier NP through Yellowstone NP including=20
portions of the Sawtooth/Salmon River ranges, Absarokas, terrain of
NW WY, northern Utah, and into the Park Range of CO. Here, WPC=20
probabilities Day 2 and 3 reach above 70% for 8+ inches, and Day 2=20
and Day 3 snowfall could be impressive above generally 6000 ft=20
where locally 1-2 feet is possible.

Miller/Weiss




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!4ONBRMdITod6KQZeFxmplUpEcL6FhhdNmsyM3cstn2js_= 1Nv2iBrrRRCa5z0OsCbPZ1yd7WcRTVv4VpGUAMNxmUzroo$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 040755
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
255 AM EST Thu Dec 4 2025

Valid 12Z Thu Dec 04 2025 - 12Z Sun Dec 07 2025


...Great Lakes & Northeast...
Days 1-3...

A progressive and flow pattern over the Great Lakes will result in
periodic episodes of snow squalls and LES bands as a -AO/NAO regime
cuts off a large upper low over southeast Canada and builds a ridge
over Greenland and the Davis Strait. Today, an Arctic front=20
traversing the Great Lakes will act as a trigger at low-levels at
the same as the divergent left-exit region of a 250mb jet streak
places itself over the Northeast. Latest NAM shows 0-2km FGEN along
the front that is paired with a well-saturated low-level profile
and SBCAPE as high as 300 J/kg. As the front traverses the region,
the DGZ will grow within the 900-800mb layer and squalls will be
capable of producing bursts of heavy snow and gusty winds. While
snow accumulations will likely be limited in most cases due to the
squalls' progressive movement, surface and road temperatures=20
around freezing will drop into the 20s in wake of the front,=20
allowing for untreated surfaces to become icy and hazardous.=20
Whether it be by snow accumulating on all surfaces, melting and=20
refreezing on untreated surfaces, or the rapid reductions in=20
visibility, snow squalls have the potential to produce dangerous=20
driving conditions in the matter of seconds. WPC continues to issue
Key Messages for the snow squall threat for today (see Key=20
Messages link below).

In wake of the Arctic frontal passage, a pair of sheared shortwave
troughs within a broad cyclonic flow pattern will direct a pair of
frontal systems across the Great Lakes. Rounds of light-to-moderate
snowfall will ensue over the Upper Great Lakes Thursday night and
into Friday, with another cold kicking up additional LES bands in
the typical LES belts of the region. WPC probabilities show low-
to-moderate chances (30-50%) for snowfall totals >4" through Friday
and Saturday in Michigan's U.P., the western LES band belts of
Michigan's Mitten, and downwind of Lakes Erie and Ontario.


...Mid-South to the Mid-Atlantic...=20
Days 1-2...

Guidance is coming into better agreement on a winter setup that
is likely to produce some of the first winter hazards of the season
from the Mid-South to the Mid-Atlantic beginning today and lasting
through Friday. A shortwave trough over the south-central Plains=20
today will weaken as it makes its way east. Despite this 500mb=20
trough losing its punch, a strong ridge of high pressure over the=20
Bahamas and a large upper-low over Hudson Bay has led to the=20
formation of a robust 250mb jet streak oriented SW-NE over the=20
east-central U.S.. Beneath the diffluent right-entrance region, a=20
weak wave of low-pressure along central Gulf Coast will escort a=20
plume of Gulf moisture northeastward into a frigid air-mass of=20
early December. Overrunning moisture along a narrow 925-850mb front
from central AR on east to the southern Appalachians is set to=20
give rise to a potentially disruptive wintry mix. Ice accumulations
from the Little Rock-Memphis-Nashville metro areas will be light,=20
but given it is the first icing setup of the season, untreated=20
roads may become slick and treacherous for travelers, especially=20
for the Thursday PM rush hour and overnight Thursday.=20

As the upper trough approaches the Mid-Atlantic Thursday night,=20
enhanced 290K isentropic ascent and increasing 850-700mb WAA aloft=20
will foster periods of snow to develop from the central=20
Appalachians and Blue Ridge of WV/VA on east across the=20
central/southern VA Piedmont Thursday night and into Friday=20
morning. Similar to the Mid-South, this will be the first=20
accumulating snow of the season, likely resulting in hazardous=20
travel conditions on untreated surfaces. Farther south, an icy=20
over-running setup looks to unfold from the southern Appalachians=20
on east across northern NC. A wintry mix is likely to cause some=20
minor ice accumulations on roads, sidewalks, and vegetation Friday=20
morning and could cause travel delays.

WPC probabilities show moderate chances (40-60%) for snowfall=20
totals >2" from the Central Appalachians to south-central VA, which
does include portions of the Richmond, VA metro area. Localized
amounts topping 4" are possible in the Blue Ridge Mountains of
southwest VA. In terms of ice accumulations, most areas from the
Mid-South to the Mid-Atlantic can expect ice accumulations less
than a tenth of an inch, although some of the southern Appalachians
of NC could see localized amounts approach one-tenth. The WSSI does
depict localized areas of Minor Impacts through Friday.


...Pacific Northwest, Northern & Central Rockies...
Days 1-3...

A highly active storm track into the Northwest will usher in
copious amounts of Pacific moisture from the Pacific Northwest on
east into the Northern and Central Rockies. Starting today, a
steady barrage of >90th climatological percentile PWATs will stream
across the Pacific Northwest and will over into the Great Basin=20
and Rockies through Friday and linger into Saturday. Synoptic-scale
forcing will be present throughout the Northern Rockies through=20
Friday, then over the Central Rockies late Friday into Saturday as
a stubborn NW-SE oriented 250mb jet streak places its diffluent=20
left-exit region overhead. Snow levels over the Pacific Northwest=20
will dip as low as 3,000ft while the Northern Rockies generally=20
hover around 4,000ft. As height falls ensue on Friday and continue
into Saturday, snow levels will drop to as low as 2,000ft,=20
although the heaviest snowfall will be confined to elevations above
5,000ft in the Bitterroots, Lewis Range, and Sawtooth, above=20
6,000ft in the Tetons, Absaroka, Big Horns, Bear River, and Wasatch
Ranges, and above 7,000ft in the central WY/CO Rockies.=20

Probabilities become even more impressive Day 2 and 3 across the=20
higher terrain from Glacier NP through Yellowstone NP including=20
portions of the Sawtooth/Salmon River ranges, Absarokas, terrain of
NW WY, northern Utah, and into the Park Range of CO. Here, WPC=20
probabilities Day 2 and 3 reach above 70% for 8+ inches, and Day 2=20
and Day 3 snowfall could be impressive above generally 6000 ft=20
where locally 1-2 feet is possible. Over the next few days, WPC
probabilities paint a wintry picture across many of the Northern
and Central Rockies, as well as the higher elevations of the=20
Cascades (above 5,000ft) with high chances (>70%) for snowfall
totals >12" in all of these listed ranges and elevations through
Saturday. In fact, the higher elevations of the Lewis Range,
Bitterroots, and Tetons have moderate-to-high chances (50-80%) for
snowfall totals >24". The WSSI shows many areas of Minor Impacts=20
of the Northern and Central Rockies, including some Moderate to=20
locally Major Impacts. The Major Impact potential areas=20
(considerable disruptions; dangerous travel and widespread=20
closures) along the Wasatch east of Salt Lake City. Residents in=20
these mountain ranges should prepare for a multi-day stretch of=20
winter weather that results in difficult and treacherous travel=20
conditions.

...Midwest...
Day 3...

The active pattern of Pacific moisture and disturbances traversing
the Northwest will result in at least one of these disturbances
reaching the Midwest late Friday night and into Saturday. A general
model consensus agrees a slug of rich Pacific moisture within the
700-300mb layer will advance across the northern Great Plains and
reach the Missouri River Valley by Saturday. This is where the
agreement in guidance ends, however, as individual guidance members
(including ensembles) disagree upon the strength and track of this=20
storm as it reaches the Central Plains on Saturday. The synoptic-=20
scale setup should foster an 850mb low with sufficient 850-700mb=20
FGEN to give rise to a band of moderate-to-heavy snow, but exactly=20
where this band sets up is low confidence.=20

At the moment, WPC probabilities show minor snowfall totals (1-3")
generally having moderate-to-high chances (30-50%) across the=20
northern High Plains through Saturday morning. The high degree of=20
spread in model solutions is causing WPC probabilities to sport low
chances (10-30%) for snowfall totals >4" from southeast SD and=20
northeast NE on east through southern MN and northern IA. That=20
being said, the favorable synoptic and mesoscale processes at play=20
could very much support a band of >6" snowfall totals that causes=20
travel headaches for residents in the Midwest. Those in the Midwest
should continue to monitor the forecast closely as more snow is in
the forecast and is likely to cause some travel headaches (WSSI-P=20
shows 40-60% chances for Minor Impacts from southeast SD and=20
northeast NE on east through southern MN and northern IA) but=20
details as to which areas are likely to see the worst impacts are=20
still unclear at this time.

Mullinax


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-wJ58ymkpysFxygKi1ghMuAJzz62G2BeQhLjLlRE1QtRe= gwW2cnJ4DMLjWxp4ol_eRJ292Trto_NlWn0sb-kn78UBsc$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 042010
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
310 PM EST Thu Dec 4 2025

Valid 00Z Fri Dec 05 2025 - 00Z Mon Dec 08 2025


...Great Lakes...
Days 1-3...

Periodic mid/upper level impulses rotating within a broad cyclonic
flow pattern will continue to support rounds of light-to-moderate
lake effect snowfall across the upper Great Lakes the next few
days. WPC probabilities continue to show low-to-moderate chances
(30-60%) for snowfall totals >4" each day Friday through Sunday,
primarily across eastern portions of the U.P. of Michigan as well
as northern parts of Michigan's Mitten. Slightly higher
probabilities for lower snowfall amounts exist downwind of Lake
Erie and Lake Ontario on Sunday.


...Mid-South to the Mid-Atlantic...
Day 1...

The first winter hazards of the season from the Mid-South to the
Mid-Atlantic continue tonight into Friday as a developing wave of
low pressure along the central Gulf Coast escorts a plume of Gulf
moisture northeastward into a frigid air-mass for early December.
Overrunning moisture along a narrow 925-850mb front from central AR
on east to the southern Appalachians is set to give rise to a
potentially disruptive wintry mix. Ice accumulations from the
Little Rock-Memphis-Nashville metro areas will be light, but given
it is the first icing setup of the season, untreated roads may
become slick and treacherous for travelers through the overnight
hours tonight.

As weak low pressure slides eastward along the Gulf Coast,
enhanced 290K isentropic ascent, increasing 850-700mb WAA aloft,
and strengthening frontogenesis will foster periods of snow to
develop from the central Appalachians and Blue Ridge of WV/VA on
east across the central/southern VA Piedmont tonight and into
Friday morning. Latest trends also suggest the northern extent of
the snow shield likely reaching into the Baltimore/Washington
Metros late tonight into early Friday morning. Similar to the Mid-
South, this will be the first accumulating snow of the season,
likely resulting in hazardous travel conditions on untreated
surfaces. Farther south, an icy overrunning setup looks to unfold
from the southern Appalachians on east across northern NC. A wintry
mix is likely to cause some minor ice accumulations on roads,
sidewalks, and vegetation Friday morning and could cause travel
delays.

WPC probabilities have increased with this forecast package, now
showing moderate to high chances (50-90%) for snowfall totals >2"
from the Central Appalachians to south-central VA, which does
include portions of the Richmond, VA metro area. Localized amounts
topping 4" are possible in the Blue Ridge Mountains of southwest VA
and southern WV. In terms of ice accumulations, most areas from
the Mid-South to the Mid-Atlantic can expect ice accumulations less
than a tenth of an inch, although some of the southern
Appalachians of NC could see localized amounts approach one-tenth.
The WSSI does depict localized areas of Minor Impacts through
Friday.


...Pacific Northwest, Northern & Central Rockies...
Days 1-3...

A highly active storm track into the Northwest will usher in
copious amounts of Pacific moisture from the Pacific Northwest on
east into the Northern and Central Rockies. A steady barrage of

90th climatological percentile PWATs will stream across the

Pacific Northwest into the Great Basin and Rockies Friday into
Sunday. Synoptic-scale forcing will be present throughout the
Northern Rockies through Friday, then over the Central Rockies late
Friday into Saturday as a persistent NW-SE oriented 250mb jet
streak places its diffluent left exit region overhead. Snow levels
over the Pacific Northwest will dip as low as 3,000ft while the
Northern Rockies generally hover around 4,000ft. As height falls
ensue on Friday and continue Saturday into Sunday, snow levels will
drop to as low as 2,000ft, although the heaviest snowfall will be
confined to elevations above 5,000ft in the Bitterroots, Lewis
Range, and Sawtooth, above 6,000ft in the Tetons, Absaroka, Big
Horns, Bear River, and Wasatch Ranges, and above 7,000ft in the
central WY/CO Rockies.

Probabilities are impressive Day 1 and 2 across the higher terrain
from Glacier NP through Yellowstone NP including portions of the Sawtooth/Salmon River ranges, Absarokas, terrain of NW WY, northern
Utah, and into the Park Range of CO. Here, WPC probabilities Day 1
and 2 reach above 70% for 8+ inches, and Day 1 and Day 2 snowfall
could be impressive above generally 6000 ft where locally 1-2 feet
is possible. Over the next few days, WPC probabilities paint a
wintry picture across many of the Northern and Central Rockies, as
well as the higher elevations of the Cascades (above 5,000ft) with
high chances (>70%) for snowfall totals >12" in all of these listed
ranges and elevations through Saturday. In fact, the higher
elevations of the Lewis Range, Bitterroots, and Tetons have
moderate-to-high chances (50-80%) for snowfall totals >24".
Moderate to heavy snow continues into Day 3, though probabilities
are less compared to Days 1 and 2. The WSSI shows many areas of
Minor Impacts of the Northern and Central Rockies, including some
Moderate to locally Major Impacts. The Major Impact potential areas (considerable disruptions; dangerous travel and widespread
closures) along the Wasatch east of Salt Lake City. Residents in
these mountain ranges should prepare for a multi-day stretch of
winter weather that results in difficult and treacherous travel
conditions.


...Midwest...
Days 2-3...

The active pattern of Pacific moisture and disturbances traversing
the Northwest will result in at least one of these disturbances
reaching the Midwest late Friday night into Saturday. A general
model consensus agrees a slug of rich Pacific moisture within the
700-300mb layer will advance across the northern Great Plains and
reach the Missouri River Valley by Saturday. While the latest
models still disagree somewhat on the strength and track of this
storm as it reaches the Central Plains on Saturday and then the
Upper Midwest Saturday night into Sunday, the synoptic-scale setup
should foster an 850mb low with sufficient 850-700mb FGEN to give
rise to a band of moderate-to-heavy snow. Right now, this appears
to be most likely from southeast South Dakota and northeast
Nebraska to southwest Minnesota and northwest Iowa.

The latest WPC probabilities have increased with this forecast,
now supporting 48-hour (Days 2-3) probabilities of 30-70% for
snowfall totals >4" for locations that banding (mentioned above) is
most likely. Additionally, 48-hour probabilities of >8", while low
(10-15%) are non-zero across southwest Minnesota and northwest
Iowa, suggesting that the favorable synoptic and mesoscale
processes at play could very much support a band of >6" snowfall
totals that cause travel headaches for residents in the Midwest.
Those in the Midwest should continue to monitor the forecast
closely as additional increases in probabilities are possible with
future forecast packages.


Miller/Mullinax





$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 050815
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
315 AM EST Fri Dec 5 2025

Valid 12Z Fri Dec 05 2025 - 12Z Mon Dec 08 2025


...Great Lakes...
Days 1-2...

Periodic mid/upper level impulses rotating within a broad cyclonic
flow pattern will continue to support rounds of light-to-moderate
lake effect snowfall across the upper Great Lakes through Saturday.
Friday features modest WAA over the Great Lakes via SWrly flow that
looks to produce periods of snow over the northwestern towns of
Michigan's Mitten, while a cold frontal passage on Saturday
revitalizes LES bands over the Michigan U.P. and downwind of Lake
Ontario over the Tug Hill. WPC probabilities show low-to-moderate
chances (30-60%) for snowfall totals >4" over northwest mainland
Michigan today. By Saturday, most snowfall totals over the eastern
Michigan U.P. and downwind of Lake Ontario is likely to range
between 1-4".


...Mid-Atlantic...
Day 1...

The first winter hazards of the season for much of the Mid-
Atlantic is unfolding this morning. As weak low pressure slides
eastward over the Southeast, enhanced 290K isentropic ascent,
increasing 850-700mb WAA aloft, and strengthening low-level frontogenesis
is producing periods of snow from the central Appalachians and
Blue Ridge of WV/VA on east across the central/southern VA Piedmont
and across the DelMarVa Peninsula. Light snow is advancing as far
north as the Washington D.C./Baltimore metro areas, which is
may result in slick roads for the Friday AM commute. This will be
the first accumulating snow of the season, likely resulting in
hazardous travel conditions on untreated surfaces across much of
the Mid-Atlantic. Farther south, an icy overrunning setup looks to
unfold from the southern Appalachians on east across northern NC.
A wintry mix is likely to cause some minor ice accumulations on
roads, sidewalks, and vegetation Friday morning and could cause
travel delays. Snow should taper off by mid-afternoon with
lingering icy conditions across affected areas of the Mid-Atlantic
through Friday night.

Snowfall accumulations are likely to range between 1-4" from
southern WV and southwest VA across southern VA (including the
Richmond metro area) and into the lower DelMarVa Peninsula.
Localized totals >4" are possible in the Blue Ridge Mountains of
southwest VA. In terms of ice accumulations, most areas from the
VA/NC Blue Ridge on east across southern VA and northern NC can
expect minor accumulations less than a tenth of an inch, although
some of the southern Appalachians of NC could see localized amounts
approach one-tenth. The WSSI does depict Minor Impacts through
Friday afternoon for most areas referenced in this discussion with
some localized Moderate Impacts in the southern VA Piedmont.


...Pacific Northwest, Northern & Central Rockies...
Days 1-3...

A highly active storm track into the Northwest will usher in
copious amounts of Pacific moisture from the Pacific Northwest on
east into the Northern and Central Rockies. A steady barrage of

90th climatological percentile PWATs will stream across the

Pacific Northwest into the Great Basin and Rockies today, with
another round of >90th percentile PWATs arriving in the Pacific
Northwest on Sunday. Synoptic-scale forcing will be located over
the Northern Rockies today, then over the Central Rockies Friday
night into Saturday as a persistent NW-SE oriented 250mb jet
streak places its diffluent left exit region overhead. Snow levels
over the Pacific Northwest will dip as low as 3,000ft while the
Northern Rockies generally hover around 4,000ft. As height falls
transpire today over the Northwest and continue through Saturday,
snow levels will drop to as low as 2,000ft, although the heaviest
snowfall will be confined to elevations above 5,000ft in the
Bitterroots, Lewis Range, and Sawtooth, above 6,000ft in the
Tetons, Absaroka, Big Horns, Bear River, and Wasatch Ranges, and
above 7,000ft in the central WY/CO Rockies. Snow looks to taper off
across the Central Rockies by Saturday evening, but the next
atmospheric river will deliver another plume of Pacific moisture
across the Pacific Northwest and northern Rockies on Sunday.

WPC probabilities are impressive Day 1 and 2 across the higher
terrain from Glacier NP through Yellowstone NP including portions
of the Sawtooth/Salmon River ranges, Absarokas, terrain of NW WY,
northern Utah, and into the Park Range of CO. Here, WPC
probabilities Day 1 and 2 reach above 70% for 8+ inches, and Day 1
and Day 2 snowfall could be impressive above generally 6000 ft
where locally 1-2 feet is possible. Over the next few days, WPC
probabilities paint a wintry picture across many of the Northern
and Central Rockies, as well as the higher elevations of the
Cascades (above 5,000ft) with high chances (>70%) for additional snowfall totals >18" in all of these listed ranges and elevations through
Saturday. In fact, the higher elevations of the Lewis Range,
Bitterroots, and Tetons have moderate-to-high chances (50-80%) for
snowfall totals >24". Moderate to heavy snow continues into Day 3
over the WA Cascades and northern Rockies, though probabilities
suggest less snowfall compared to the more snowy stretches on
Friday and Saturday. The WSSI shows many areas of Minor and
Moderate Impacts across the Northern and Central Rockies,
including some locally Major Impacts. The Major Impact potential
areas (considerable disruptions; dangerous travel and widespread
closures) include areas along the Wasatch east of Salt Lake City
and the more remote areas of these Intermountain West ranges.
Residents in these mountain ranges should prepare for a multi-day
stretch of winter weather that results in difficult and treacherous
travel conditions.

...Northern Plains & Midwest...
Days 2-3...

The active pattern of Pacific moisture and disturbances traversing
the Northwest will result in at least one of these disturbances
reaching the Midwest late Friday night into Saturday. A slug of
rich Pacific moisture within the 700-300mb layer will advance
across the northern Great Plains and reach the Missouri River
Valley by Saturday. The synoptic-scale setup favors the development
of an 850mb low with sufficient 850-700mb FGEN and WAA to the north
and east of the 850mb low track to support a band of moderate-to-
heavy snow. The band of snow starts out Saturday morning across
the Dakotas, then heads for southern MN and northern IA by late
Saturday afternoon and evening, and begins to weaken in intensity
by early Sunday morning the snow reaches the Lower Great Lakes and
OH Valley.

The latest WPC probabilities have increased with this forecast,
now supporting probabilities of 50-70% for snowfall totals >4" for
locations that banding (mentioned above) is most likely across the
Midwest. However, given the favorable synoptic and mesoscale
processes at play, a band of >6" snowfall totals that cause travel
headaches for residents in the Midwest is very much on the table,
as evident in the low-to-moderate chances (20-50%) for snowfall
totals >6" over northern IA. Those in the Midwest should continue
to monitor the forecast closely as additional changes in the
placement and totals of the heaviest snowfall could still change
over the next 24 hours.

...Northeast...
Day 3...

There remains a good deal of uncertainty in the forecast
on Sunday with the GFS remaining aggressive in a more
amplified/phase solution compared to the ECMWF/CMC. The GFS is also
noticeably wetter than the GEFS over the Northeast. The ECMWF/CMC
camp shows a broader and less amplified 500mb trough over the Great
Lakes and southeast Canada, but enough 500mb PVA and lake-enhanced
snowfall bands are showing low chances (10-30%) for snowfall
totals >4" downwind of Lakes Erie and Ontario. Some minor impacts
to travel are possible as denoted by the WSSI-P showing low-to-
moderate chances (30-60%) for Minor Impacts on Sunday.

Mullinax




$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 052005
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
305 PM EST Fri Dec 5 2025

Valid 00Z Sat Dec 06 2025 - 00Z Tue Dec 09 2025


...Pacific Northwest, Northern & Central Rockies...
Days 1-3...

A highly active storm track with several significant atmospheric
rivers into the Northwest will usher in copious amounts of Pacific
moisture from the Pacific Northwest on east into the Northern and
Central Rockies the next few days. A steady barrage of >90th
climatological percentile PWATs will stream across the Pacific
Northwest into the Great Basin and Rockies through Saturday, with
another round of >90th percentile PWATs arriving in the Pacific
Northwest Sunday into Monday. Synoptic-scale forcing for ascent
will be aided by a persistent NW-SE oriented 250mb jet streak with
its diffluent left exit region overhead. Snow levels over the
Pacific Northwest will dip as low as 3,000ft while the Northern
Rockies generally hover around 4,000ft. As height falls occur over
the Northwest through Saturday, snow levels will drop to as low as
2,000ft. That being said, the heaviest snowfall will be confined to
elevations above 5,000ft in the Bitterroots, Lewis Range, and
Sawtooth, above 6,000ft in the Tetons, Absaroka, Big Horns, Bear
River, and Wasatch Ranges, and above 7,000ft in the central WY/CO
Rockies. Snow looks to taper off across the Central Rockies by
Saturday evening, but the next atmospheric river will deliver
another plume of Pacific moisture and another round of heavy
mountain snowfall across the Pacific Northwest and northern Rockies
Sunday into Monday.

WPC probabilities continue to be impressive on Day 1 across the
higher terrain from Glacier NP through Yellowstone NP including
portions of the Sawtooth/Salmon River ranges, Absarokas, terrain of
NW WY, northern Utah, and into the Park Range of CO. Here, WPC
probabilities reach above 70% for 8+ inches, with locally higher
amounts of 1-2 feet generally above 6000 ft. Over the next few
days, WPC probabilities paint a wintry picture across many of the
Northern and Central Rockies, as well as the higher elevations of
the Cascades (above 5,000ft) with high chances (>70%) for
additional snowfall totals >18" in all of these listed ranges and
elevations through Sunday. In fact, the higher elevations of the
Lewis Range, Bitterroots, and Tetons have moderate-to-high chances
(50-80%) for snowfall totals >24". Moderate to heavy snow continues
later into Days 2 and 3 over the WA Cascades and northern Rockies,
though probabilities suggest less snowfall compared to the more
snowy stretches tonight into Saturday. The WSSI shows many areas of
Minor and Moderate Impacts across the Northern and Central
Rockies, including some locally Major Impacts. The Major Impact
potential areas (considerable disruptions; dangerous travel and
widespread closures) include areas along the Wasatch east of Salt
Lake City and the more remote areas of these Intermountain West
ranges. Residents in these mountain ranges should prepare for a
multi-day stretch of winter weather that results in difficult and
treacherous travel conditions.

...Northern Plains & Midwest...
Days 1-2...

A fast-moving clipper system, aided by a slug of Pacific moisture
combined with strengthening low-level frontogenesis and warm
advection, will support a swath of moderate to heavy snow from the
northern Plains into the Midwest the next couple of days. The band
of snow first starts to develop across the Dakotas late tonight
into Saturday morning, then heads for southern MN and
northern/central IA as it intensifies late Saturday afternoon and
evening. The band then begins to weaken by early Sunday morning as
the snow reaches the Lower Great Lakes and OH Valley.

The latest WPC probabilities have increased with this forecast,
now supporting probabilities of 50-90% for snowfall totals >4" for
locations that banding (mentioned above) is most likely across the
Midwest. However, given the favorable synoptic and mesoscale
processes at play, a swath of heavier and more impactful snow still
remains on the table, as evident in the low-to-moderate chances
(30-50%) for snowfall totals >6" over northern/central IA. By
Sunday, low probabilities (10-40%) of >4" of snow extend into
southern Wisconsin and northern Illinois as the quick-moving wave
weakens on its track into the Lower Great Lakes and OH Valley.
Those in the Midwest should continue to monitor the forecast
closely as additional changes in the placement and totals of the
heaviest snowfall could still change over the next 24 hours.

...Great Lakes & Northeast...
Days 1-3...

Periodic mid/upper level impulses rotating within a broad cyclonic
flow pattern will continue to support rounds of light-to-moderate
lake effect snowfall across the upper Great Lakes through Monday. A
cold frontal passage Saturday into early Sunday morning
revitalizes LES bands over the Michigan U.P. and downwind of Lake
Ontario over the Tug Hill. Then, the fast-moving clipper from the
Midwest races across the Great Lakes and Northeast later Sunday
into Monday, bringing more lake effect snow and likely a period of
steadier synoptic snow to interior portions of the Northeast and
northern New England. The latest 12Z guidance continues to suggest
a fairly flat mid/upper level shortwave as it passes over the
region, which would limit snowfall potential. That said, it would
not be surprising to see models trend a bit more amplified and more
snowy in future model cycles, so continue to monitor the forecast
in the coming days.

WPC probabilities show overall low chances (10-40%) of >4" of snow
across portions of northern Michigan downwind of Lake Superior and
Lake Michigan Saturday into Sunday. Low chances (10-30%) of >4" of
snow then extend downwind of Lake Erie and Lake Ontario and across
parts of northern New England Sunday into Monday.


Miller/Mullinax







$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 060746
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
246 AM EST Sat Dec 6 2025

Valid 12Z Sat Dec 06 2025 - 12Z Tue Dec 09 2025

...Central Rockies..
Day 1...

500mb height falls, the divergent left-exit region of a strong
250mb jet streak, and a plume of anomalous PWATs (above the 90th
climatological percentile per ECMWF) are all working together to
produce heavy mountain snow from the Wasatch, Uinta, and Wind River
ranges to the Rockies of southern WY and much of CO. Upslope
enhancement will be focused along the Wasatch and CO/WY Rockies
through this morning. As the core of the best moisture content
exits east this afternoon, snow will gradually taper off Saturday
night. WPC probabilities sport high chances (>70%) for additional
snowfall totals >12" in the Wasatch above 8,000ft and CO/WY
Rockies above 9,000ft. WPC's WSSI highlights Moderate Impacts at
these listed elevations with some localized Major Impacts in the
more remote peaks of the UT, WY, and CO Rockies.


...Pacific Northwest & Northern Rockies...
Days 1-3...

The Pacific Northwest and Northern Rockies will continue to contend
with the lingering effects of the ongoing atmospheric river (AR)
through the remainder of the day Saturday. WPC probabilities show
high chances (>70%) for additional snowfall totals >8" in the more
remote reaches of the WA Cascades, the Bitterroots, Lewis Range,
and as far south as the peaks of the Absaroka and Tetons. A brief
ridge of high pressure builds in Saturday night before the round
of Pacific moisture arrives Sunday morning. Temperatures will be a
little milder this time around, confining most snowfall to the more
remote reaches of the Cascades. Pacific moisture will spill over
into the Northern Rockies Sunday night as the next atmospheric
river arrives on Monday. The Monday AR will be more intense with a
plume of >99th climatological PWATs engulfing much of the Pacific
Northwest by Monday afternoon. While the moisture influx is more
extensive, the strength of the WAA will keep snowfall to the more
remote reaches of the Cascades. However, moisture that spills over
into the Bitterroots and Lewis Range will have enough cold air to
support locally heavy snowfall. Over this weekend and through
Monday, WPC probabilities show moderate-to-high chances (50-80%)
for snowfall totals >12" in the WA Cascades above 5,000ft and along
the Lewis Range, which does include Glacier NP. Expect any
mountain passes that remain open to contend with potential closures
this weekend and into early next week.

...Northern Plains & Midwest...
Days 1-2...

Height falls ahead of an approaching 500mb vorticity maximum will
coincide with the divergent left-exit region of a 250mb jet streak
over the Northern Plains to support the development of low pressure
early this morning. A narrow band of 850mb WAA and FGEN over
eastern MT will pivot south and east towards southern ND and become
responsible for the initial band of snow this morning. As low
pressure deepens, a more organized 850mb low will form over
southern SD and central NE. A strengthening 850mb LLJ will direct a
surge of WAA in the 850-700mb layer ahead of the 850mb low.
Combined with a healthy 290K isentropic ascent amid SWrly flow, and
a moistening DGZ will ensue over southeast SD, northern IA, and
southern MN and periods of heavy snow will develop. WPC's Snowband
Probability Tracker depicts the potential for >1"/hr snowfall
rates over southeast SD beginning around midday and continuing over
northern IA through Saturday evening. After 00Z Sunday, the 850mb
low will weaken, taking on a positive tilt and becoming an open
wave. Light-to-moderate snow is expected through Saturday night
over northern IL and southern WI (including the Milwaukee and
Chicago metro areas), with light snow possible across the Great
Lakes on Sunday.

WPC probabilities show northern IA as having the best odds of
seeing the heaviest snowfall of the event with moderate chances
(40-60%) for snowfall totals >6". Probabilities suggest I-35
located north of Des Moines and south of I-90 have low chances
(10-20%) for localized amounts over 8". Elsewhere, the area
spanning Sioux Falls on south and east through southern MN and
eastern ND all sport >50% chances for >4" of snowfall. The WSSI
shows Minor Impacts from the Sioux Falls area of southeast SD to as
far east as the Milwaukee/Chicago metro areas due to the snowfall
Saturday night into Sunday morning. Across eastern MT and southwest
ND, WPC probabilities show low- to- moderate chances (30-50%) for
snowfall >2", but probabilities for >4" are generally <10%,
implying that most totals are likely to range between 1-4" through
Saturday afternoon.

It is worth noting bitterly cold temperatures will follow in wake
of this system Saturday night and through Sunday. By Sunday
morning, temperatures will be in the single digits across much of
the Midwest and lows below zero Sunday night. Any snow that falls
will likely stick around for a couple days, resulting in daily
recurrences of icy roads and the potential for black ice.

...Great Lakes & Northeast...
Days 1-3...

A series of upper level disturbances tracking across the Great
Lakes and into the Northeast will cause both LES bands and some synoptically-focred snow across these regions this weekend and into
early next week. Some LES streamers off Lakes Superior, Erie, and
Ontario will keep accumulating snow in the forecast in the usual
snow belts of Michigan's U.P., the "Tip of the Mitt" in Michigan,
and across western NY. By Sunday morning the upper trough
responsible for the Midwest storm on Saturday will make its way
through these regions with light-to-moderate snowfall across
Michigan and much of the Northeast (minus the I-95 corridor
megalopolis). Most snowfall totals will range between 1-4",
although some of the LES belts may manage to see some snowfall
totals eclipse 4" on Sunday. It is possible an inverted trough axis
over the Gulf of Maine could produce locally heavy snow along the
coast of ME, but the trough is a progressive one and should limit
totals from being overly heavy (1-4" most likely). Lastly, while
high pressure builds in over the Northeast on Monday, an Alberta
Clipper makes its way toward the Upper great Lakes by Monday
evening with more light-to-moderate snow expected.

WPC probabilities over the next three days (Sat-Sun-Mon) show
moderate-to-high chances (50-80%) for snowfall totals >4" in the
typical LES belts of Michigan's U.P., northern Michigan, and
downwind of Lakes Erie and Ontario. When it comes to >8" of
snowfall, it is the eastern Michigan U.P. and northwest Michigan
where low-to-moderate chances (30-50%) are present. The WSSI shows
Minor Impact potential downwind of Lakes Erie and Ontario, which
does include the Buffalo metro area.

...Southern Appalachians...
Days 2-3...

A quick moving 500mb trough will track from the TN Valley Sunday
night to the Southeast Coast by Monday afternoon. 500mb PVA ahead
of the upper trough will be paired with easterly low-level flow
that allows for some upslope enhancement along the southern
Appalachians. Snow will be at its heaviest Monday morning but taper
off by Monday evening. WPC probabilities show low-to-moderate
chances (30-50%) for snowfall totals >2" in portions of the VA/NC
Blue Ridge and Potomac Highlands of WV. Some localized totals could
top 4" in the VA/NC Blue Ridge.


Mullinax




$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 061854
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
154 PM EST Sat Dec 6 2025

Valid 00Z Sun Dec 07 2025 - 00Z Wed Dec 10 2025


...Pacific Northwest & Northern Rockies...
Days 1-3...

The Pacific Northwest and Northern Rockies will continue to contend
with the lingering snow during the D1 period as a shortwave tracks
across the region over a broad western U.S. ridge ahead of a strong
atmospheric river (AR) set to surge into WA/OR on D2, with lowering
snow levels across the Cascades on D3. Snow levels largely start
out low around 3,000-4,000 ft, but rapidly rise across the Pacific
Northwest on Sunday above 5,000 ft and as the strong AR approaches
on Monday these values increase to above 6,000 ft in the northern
WA Cascades and above 7,000 ft from Mt. Rainer southward.
Meanwhile, snow levels also rise across the northern Rockies to
above 5,000-6,000 ft as well before dropping on D3 as the AR ends
and the associated shortwave ejects into the northern Plains. For
the 72-hr period ending 00z 12/10, WPC probabilities for more than
12 inches are high (70-90%) across the WA Cascades above 6,000 ft,
as well as parts of the northern Rockies in ID, northwest MT, and
northwest WY above 6,000-7,000 ft.


...Midwest/Great Lakes/Northeast...
Days 1-3...

Fast-moving clipper system currently impacting parts of the
northern Plains and Midwest with heavy snow this afternoon will
swing across IA/northern IL/southern WI tonight into early Sunday
and produce a storm total swath of up to 4-8 inches of fresh
snowfall. Height falls ahead of an approaching 500mb vorticity
maximum will coincide with the divergent left-exit region of a
250mb jet streak to support the developing low pressure system. A
strengthening 850mb LLJ will direct a surge of WAA in the 850-700mb
layer ahead of the 850mb low. Combined with a healthy 290K
isentropic ascent amid SWrly flow, and a moistening DGZ will ensue
over northern IA this evening and periods of heavy snow will
develop. Snowfall rates may briefly exceed 1"/hr within this east-
west corridor just north of the 850mb FGEN extending from northern
IA into southern WI/northern IL. However, the 850mb low will begin
to quickly weaken tonight, taking on a positive tilt and becoming
an open wave. Light- to- moderate snow is expected through Sunday
morning into northern IN and the southern L.P. of MI.

WPC probabilities beginning at 00z Sunday show eastern IA to
northern IL (including the Chicago metro) as having the highest
chances (40-80%) for snowfall totals more than 4 inches. It is
worth noting bitterly cold temperatures will follow in wake of this
system Saturday night and through Sunday. By Sunday morning,
temperatures will be in the single digits across much of the
Midwest and lows below zero Sunday night. Any snow that falls will
likely stick around for a couple days, resulting in daily
recurrences of icy roads and the potential for black ice.

This system along with another upper level disturbance by D3 tracking
across the Great Lakes and into the Northeast will cause both LES
bands and some synoptically- forced snow across these regions
Sunday and into early next week. Some LES streamers off Lakes
Superior, Erie, and Ontario will keep accumulating snow in the
forecast in the usual snow belts of Michigan's U.P., the "Tip of
the Mitt" in Michigan, and across western NY. By Sunday morning the
upper trough responsible for the Midwest storm on Saturday will
make its way through these regions with light-to- moderate snowfall
across Michigan and much of the Northeast (minus the I-95 corridor megalopolis). Most snowfall totals will range between 1-4",
although some of the LES belts may manage to see some snowfall
totals eclipse 4" on Sunday. Lastly, while high pressure builds in
over the Northeast on Monday, an Alberta Clipper makes its way
toward the Upper Great Lakes by Monday evening with more light-to-
moderate snow expected. Strong southerly flow ahead of this system
may actually produce a band of heavy lake effect snow oriented from
Lake Michigan aimed northward into the eastern U.P.

WPC probabilities over through Tuesday show moderate-to-high
chances (50-80%) for snowfall totals >4" in the typical LES belts
of Michigan's U.P., northern Michigan, and downwind of Lakes Erie
and Ontario. When it comes to >8" of snowfall, it is the eastern
Michigan U.P. where moderate chances (50-70%) are present.


...Southern Appalachians & Mid-Atlantic...
Day 2...

A quick moving 500mb trough will track from the TN Valley Sunday
night to the Southeast Coast by Monday afternoon. 500mb PVA ahead
of the upper trough will be paired with easterly low-level flow
that allows for some upslope enhancement along the southern
Appalachians. Snow will be at its heaviest Monday morning but taper
off by Monday evening. As the upper trough sharpens on Monday over
the Mid-Atlantic and low pressure deepens over the Gulf Stream off
the Southeast coastline, some snow may also extend eastward into
southern VA and far northern NC. QPF and therefore snow amounts
have trended up with the latest guidance and should be monitored
over the next day or so for potentially impactful accumulating
snowfall. WPC probabilities currently show low- to- moderate
chances (30-50%) for snowfall totals >2" in portions of the VA/NC
Blue Ridge and Potomac Highlands of WV. Some localized totals could
top 4" in the VA/NC Blue Ridge.


...Northern Plains & Upper Midwest...
Day 3...

By the second half of D3 (12z 12/9-00z 12/10) a potent shortwave
within the divergent left-exit region of a strong upper jet
extending as far westward as the central Pacific Ocean will enter
the northern Plains and likely produce a narrow stripe of heavy
snowfall. Snow will be associated with WAA on the front-end and a
trailing inverted trough. The thermal gradient will be tight and
support intense snowfall rates at times just north of the warm
front, but with uncertainty remaining as guidance maintains some
latitudinal spread and timing differences in the low track. Strong
winds are also likely on the backside of the system as models
deepen this low into the 980s, so blowing snow could be a concern
should these winds overlap with a snowpack. Current WPC
probabilities for more than 4 inches of snow through 00z Wednesday
are moderate (40-70%) across north-central ND through central MN.
However, additional snow is likely after 00z Wednesday and
continuing further east into WI and the Great Lakes region.


Mullinax/Snell





$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 070816
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
316 AM EST Sun Dec 7 2025

Valid 12Z Sun Dec 07 2025 - 12Z Wed Dec 10 2025


...Pacific Northwest & Northern Rockies...
Days 1-3...

The Pacific Northwest and Northern Rockies will face a steady
barrage of Pacific moisture over the next few days thanks to a
multi-day strong atmospheric river that is pinned between a strong
subtropical ridge off the coast of CA and a stalled, positively-
tilted upper low in the Gulf of AK. Today, PWATs start out around
the 90th climatological percentile throughout the Northwest, before
a more impressive plume of PWATs above the 99th climatological
percentile stream in on Monday. Even on Tuesday, as the subtropical
ridge expands a little farther north, a fire-hose of Pacific
moisture will continue into the Pacific Northwest that spills into
the Northern Rockies as well. Add in steady synoptically-forced
ascent aloft from a strong 250mb jet stream and persistent upslope
flow into many of these mountains ranges, and the recipe is for
heavy snowfall from the Olympics and Cascades to the western WY
Rockies.

Today, snow levels largely look to start out around 3,000-4,000
ft, but rapidly rise across the Pacific Northwest above 5,000ft.
As the strong AR and its associated WAA aloft approaches on
Monday, these values increase to above 6,000 ft in the northern WA
Cascades and above 7,000 ft from Mt. Rainer and points south.
Farther east, snow levels will rise across the northern Rockies as
well, topping 6,000ft in many cases before falling on D3 as the AR
orients itself farther south as a shortwave trough ejects into the
northern Plains. Starting this morning and lasting through early
Wednesday morning, 72-hr WPC probabilities for more than 12 inches
are high (70-90%) across the WA Cascades above 5,000 ft, as well
as parts of the northern Rockies in ID, western MT, and western WY
above 6,000-7,000 ft. WPC probabilities even show speckled areas
of low-to-moderate chances (20-50%) for localized snowfall totals

30" in the more remote reaches of these regions through Tuesday

night.


...Great Lakes & Northeast...
Days 1-3...

This morning, the upper trough responsible for the Midwest storm
on Saturday will generate light-to-moderate snowfall across
Michigan and much of the Northeast (minus the I-95 corridor
megalopolis). Most snowfall totals will range between 1-4",
although some areas within the Tug Hill and Adirondacks may manage
to see localized snowfall totals eclipse 4" on Sunday. The upper-
level disturbance may produce a small area of low pressure off the
Maine coast that produces a fast moving band of snow over Downeast
Maine Sunday night. WPC probabilities do depict low chances
(10-30%) for snowfall totals >4" Monday night.

By Monday night, as high pressure builds in over the Northeast, an
Alberta Clipper makes its way toward the Upper Great Lakes Monday
evening with more light-to-moderate snow expected. Guidance is
coming into better agreement that strong SWrly flow ahead of the
Clipper will produce a band of heavy lake effect snow oriented from
Lake Michigan and far northwest Michigan aimed northward into the
eastern U.P.. WPC probabilities through Tuesday show moderate-to-high
chances (50-80%) for snowfall totals >4" in over the eastern
Michigan U.P. and northwest Michigan. The eastern Michigan U.P.
sports the highest chances for >8" of snowfall (30-50%). As the
Clipper's warm front moves east, sufficient 290K isentropic ascent
and 850-700mb WAA will give rise to snow over the eastern Great
Lakes and northern New England by Tuesday afternoon. Immediately
downwind of Lakes Erie and Ontario, snowfall totals will generally
range between 1-4". However, the Tug Hill has moderate chances
(40-60%) for snowfall totals >4" through early Wednesday morning.


...Southern Appalachians & Mid-Atlantic...
Days 1-2...

A quick moving 500mb trough will track from the TN Valley Sunday
night to the Southeast Coast by Monday afternoon. 500mb PVA ahead
of the upper trough will be paired with easterly low-level flow
that allows for some upslope enhancement along the southern
Appalachians. Snow will be at its heaviest Monday morning but taper
off by Monday evening. This storm could have a surprise or two up
its sleeve as the 500mb vorticity maximum reaches NC Monday
afternoon, with some guidance showing some 850mb low development
off the coast of NC's Outer Banks. Should easterly low-level winds
increase, sufficient low-level WAA and moisture advection could
create a band of snow that results in a quick hitting 1-3" snow
event from as far north as the Richmond metro area on south along
I-95 and I-85 towards the Raleigh/Durham area. WPC probabilities
currently show low chances (10-30%) for snowfall totals >4" in
portions of the VA/NC Blue Ridge and Potomac Highlands of WV, but
it is possible those chances increase should the influences of the
500mb trough prove more substantial. This has the potential to
cause slick travel conditions for the Monday evening commute in
southern VA and northern NC.


...Northern Plains & Upper Midwest...
Day 3...

By Tuesday morning, a vigorous 500mb shortwave trough with origins
from the large Gulf of AK longwave trough will race towards the
Northern Plains. Given its origins, this "Alberta Clipper" will be
more intense than most clippers. This is because it will have
exceptional synoptic-scale forcing aloft in the form of a roaring
150kt 250mb jet streak, plus anomalous moisture associated with the
strong AR over the Pacific Northwest. By 18Z Tuesday, the
clipper's MSLP looks to be sub-990mb, which ranks below the 1st
climatological percentile for this time of year. As the storm works
its way across the Dakotas Tuesday morning, impressive 290K
isentropic lift and corresponding 850-700mb FGEN will not only
help to sustain this potent clipper, but foster a potent band of
snow northeast of the 850mb low track. There is the potential for
an icy wintry mix just along and north of the surface warm front as
a protruding >0C warm nose forces snow to melt into the form of
sleet or freezing rain. But the storm's fast motion should limit
the impacts to around minor impacts (ice accretions less than a
tenth of an inch most likely).

By Tuesday night, the storm will remain in the mid-980s for
pressure as it races through WI and into MI by Wednesday morning.
WAA out ahead of the storm is likely to cause periods of snow to
envelope the eastern Great Lakes that include areas such as
northwest PA and western NY. From the Northern Plains the the Great
Lakes, not only will snow be problematic for traveling, but gusty
winds are likely to cause blowing and drifting across roads and
cause reduced visibilities. WPC probabilities show a swath of
moderate chance probabilities (40-60%) for snowfall totals >4" from
northeast ND on south and east through the Upper Midwest and the
northern half of Michigan's Mitten. Note there are also low-to-
moderate chance probabilities (20-50%) for totals >6", which does
show up on several deterministic guidance members.

While the storm's speedy forward motion should help to reduce the
chances for more prolific snowfall totals, hourly snowfall rates of

1"/hr combined with gusty winds will allow for Minor Impacts at

the very least. This is supported by the WSSI-P which depicts
moderate-to-high chances (50-70%) for Minor Impacts on Tuesday from
northern ND all the way to northern MI. Residents in the Upper
Midwest and Great Lakes should continue to monitor this storm
closely, as should residents in the Northeast as probabilistic
guidance shows measurable snowfall from this system is possible on
Wednesday.


Mullinax




$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 072021
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
321 PM EST Sun Dec 7 2025

Valid 00Z Mon Dec 08 2025 - 00Z Thu Dec 11 2025


...Pacific Northwest & Northern Rockies...
Days 1-3...

The Pacific Northwest and Northern Rockies will face a steady
barrage of Pacific moisture over the next few days thanks to a
multi-day strong atmospheric river that is pinned between a strong
subtropical ridge off the coast of CA and a stalled, positively-
tilted upper low in the Gulf of AK. Tonight, PWATs start out
around the 90th climatological percentile throughout the Northwest,
before a more impressive plume of PWATs above the 99th
climatological percentile stream in on Monday. Even on Tuesday and
Wednesday, as the subtropical ridge expands a little farther
north, a fire- hose of Pacific moisture will continue into the
Pacific Northwest that spills into the Northern Rockies as well.
Add in steady synoptically-forced ascent aloft from a strong 250mb
jet stream and persistent upslope flow into many of these mountains
ranges, and the recipe is for heavy snowfall from the Olympics and
Cascades to the western WY Rockies above the wavering high snow
levels.

Tonight, snow levels largely look to start out around 5,000ft. As
the strong AR and its associated WAA aloft approaches on Monday,
these values increase to above 6,500 ft in the northern WA
Cascades and above 7,000 ft from Mt. Rainer and points south.
Farther east, snow levels will rise across the northern Rockies as
well, topping 6,000ft in many cases before falling on Tuesday as
the AR orients itself farther south as a shortwave trough ejects
into the northern Plains. Then, snow levels once again rise on
Wednesday as levels increase above 6,000 ft from southern
Washington to west-central MT. Starting this evening and lasting
through early Wednesday evening, 72-hr WPC probabilities for more
than 12 inches are high (70-90%) across the WA Cascades above 5,000
ft, as well as parts of the northern Rockies in ID, western MT,
and western WY above 6,000-7,000 ft. WPC probabilities even show
speckled areas of low- to-moderate chances (20-50%) for localized
snowfall totals >30" in the more remote reaches of these regions
through Wednesday.


...Southern Appalachians & Mid-Atlantic...
Days 1...

A quick moving 500mb trough will track from the TN Valley Sunday
night to the Southeast Coast by Monday afternoon. 500mb PVA ahead
of the upper trough will be paired with easterly low-level flow
that allows for some upslope enhancement along the southern
Appalachians. Snow will be at its heaviest during the day on Monday
but taper off by Monday evening. As the 500mb vorticity maximum
reaches NC Monday afternoon, a weak 850mb low development off the
coast of NC's Outer Banks will allow for easterly low- level winds
to increase. This combined with sufficient low-level WAA and
moisture advection may create a band of snow that results in a
quick hitting 1-3" snow event in southern VA and northern NC as
far north as the Richmond metro area and south along I-95 and I-85
towards the Raleigh/Durham area. WPC probabilities currently show
low chances (20-40%) for snowfall totals >4" in portions of the
VA/NC Blue Ridge and Potomac Highlands of WV. Probabilities for

2" are 40-60% east of the Blue Ridge across southern VA and could

lead to slippery road conditions to start the workweek.


...Northern Plains/Upper Midwest/Great Lakes...
Days 2-3...

By Monday night, as high pressure builds in over the Northeast, the
first in a parade of "clipper" systems makes its way toward the
Upper Great Lakes with more light-to-moderate snow expected.
Guidance continues to highlight that strong SWrly flow ahead of
the Clipper will produce a band of heavy lake effect snow oriented
from Lake Michigan and far northwest Michigan aimed northward into
the eastern U.P.. WPC probabilities through Tuesday show moderate-
to- high chances (50-80%) for snowfall totals >6" in over the
eastern Michigan U.P. The eastern Michigan U.P. As the clipper's
warm front moves east, sufficient 290K isentropic ascent and
850-700mb WAA will give rise to snow over the eastern Great Lakes
and northern New England by Tuesday afternoon. Immediately
downwind of Lakes Erie and Ontario, snowfall totals will generally
range between 1-4". However, the Tug Hill has moderate chances
(40-60%) for snowfall totals >4" through early Wednesday morning.

By Tuesday morning, a vigorous 500mb shortwave trough with origins
from the large Gulf of AK longwave trough will race towards the
Northern Plains. Given its origins, this "Alberta Clipper" will be
more intense than most clippers. This is because it will have
exceptional synoptic-scale forcing aloft in the form of a roaring
150kt 250mb jet streak, plus anomalous moisture associated with the
strong AR over the Pacific Northwest. By 18Z Tuesday, the
clipper's MSLP looks to be sub-990mb, which ranks below the 1st
climatological percentile for this time of year. As the storm works
its way across the Dakotas Tuesday morning, impressive 290K
isentropic lift and corresponding 850-700mb FGEN will not only help
to sustain this potent clipper, but foster a potent band of snow
northeast of the 850mb low track. There is the potential for an icy
wintry mix just along and north of the surface warm front as a
protruding >0C warm nose forces snow to melt into the form of sleet
or freezing rain. But the storm's fast motion should limit the
impacts from freezing rain to around minor impacts (ice accretions
less than a tenth of an inch most likely).

By Tuesday night, the storm will remain in the mid-980s for
pressure as it races through WI and into MI by Wednesday morning.
WAA out ahead of the storm is likely to cause periods of snow to
envelope the eastern Great Lakes that include areas such as
northwest PA and western NY. From the Northern Plains the the Great
Lakes, not only will snow be problematic for traveling, but gusty
winds are likely to cause blowing and drifting across roads and
cause reduced visibilities. WPC probabilities show a swath of
moderate chance probabilities (40-70%) for snowfall totals >4"
from northeast ND on south and east through the Upper Midwest and
the northern half of Michigan's Mitten. Note there are also low-to-
moderate chance probabilities (20-40%) for totals >6", which does
show up on several deterministic guidance members. There has
continued to be some latitudinal spread in guidance with AIFS and
AIGFS guidance along with the operational GFS leaning towards a
more southern track that gets central MN and southern WI into
chances for heavy snow.

While the storm's speedy forward motion should help to reduce the
chances for more prolific snowfall totals, hourly snowfall rates of

1"/hr combined with gusty winds will allow for minor to moderate

impacts at the very least. This is supported by the WSSI-P which
depicts high chances (60-90%) for Minor Impacts on Tuesday from
northern ND all the way to northern MI. Residents in the Upper
Midwest and Great Lakes should continue to monitor this storm
closely, as should residents in the Northeast as probabilistic
guidance shows measurable snowfall from this system is possible on
Wednesday.


Mullinax/Snell




$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 080843
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
343 AM EST Mon Dec 8 2025

Valid 12Z Mon Dec 08 2025 - 12Z Thu Dec 11 2025


...Pacific Northwest & Northern Rockies...
Days 1-3...

The Pacific Northwest and Northern Rockies will face a steady
barrage of Pacific moisture over the next few days thanks to a
multi-day strong atmospheric river that is pinned between a strong
subtropical ridge off the coast of CA and a stalled, positively-
tilted upper low in the Gulf of AK. Today, PWATs above the 99th
climatological percentile will engulf much of the Northwest. Even
on Tuesday and into Wednesday, as the subtropical ridge expands a
little farther north, a fire-hose of Pacific moisture will continue
into the Pacific Northwest that spills into the Northern Rockies
as well. Add in steady synoptically-forced ascent aloft from a
strong 250mb jet stream and persistent upslope flow into many of
these mountains ranges, and the recipe is for heavy snowfall from
the Olympics and Cascades to the western WY Rockies above the
wavering high snow levels.

As the strong AR and its associated WAA aloft approaches on
Monday, these values increase to above 6,500 ft in the northern WA
Cascades and above 7,000 ft from Mt. Rainer and points south.
Farther east, snow levels will rise across the northern Rockies as
well, topping 6,000ft in many cases before falling on Tuesday as
the AR orients itself farther south as a shortwave trough ejects
into the northern Plains. Then, snow levels once again rise on
Wednesday as levels increase above 6,000 ft from southern
Washington to west-central MT. Through Wednesday night, 72-hr WPC
probabilities for >18" are high (>70%) across the WA Cascades
above 5,000 ft, as well as parts of western MT, and western WY
above 6,000-7,000 ft. WPC probabilities even show speckled areas of low-to-moderate chances (20-50%) for localized snowfall totals

30" in the more remote reaches of these regions through Wednesday.

...Southern Appalachians & Mid-Atlantic...
Days 1...

A 500mb trough tracking over the TN Valley this morning will race
east and off the Southeast Coast by this evening. 500mb PVA ahead
of the upper trough will be paired with easterly low-level flow
that allows for some upslope enhancement along the southern
Appalachians. Snow will be at its heaviest during the day on Monday
as Atlantic moisture is directed west to the north of a weak 850mb
low tracking across northern NC. This combined with sufficient
low-level WAA will generate a band of snow that results in a quick
hitting 1-4" snow event in southern VA and northern NC, to as far
north as the Richmond metro area and south along I-95 and I-85
towards the Raleigh/Durham area. WPC probabilities currently show
low chances (20-40%) for snowfall totals >4" in portions of the
VA/NC Blue Ridge, the Potomac Highlands of WV, and southern VA
south of the Richmond metro area. Localized snowfall totals of 5-6"
are quite possible, especially in the VA Blue Ridge. Probabilities
for >2" are 40-60% east of the Blue Ridge across southern VA and
is likely lead to slippery road conditions to start the workweek.
Latest WSSI does suggest Minor Impacts for most affected locations,
with a narrow Moderate Impacts (hazardous driving conditions) area
stretching from Roanoke, VA to the Richmond/Petersburg metro area
and as far east as Williamsburg, VA.


...Great Lakes & Northeast...
Days 1-2...

Tonight, as high pressure builds in over the Northeast, the first
in a parade of "clipper" systems tracks over the Upper Great Lakes
with more light-to-moderate snow expected. Guidance continues to
highlight that strong SWrly flow ahead of the clipper will produce
a band of heavy lake effect snow oriented from Lake Michigan and
far northwest Michigan aimed northward into the eastern U.P.. WPC
probabilities through Tuesday show moderate-to- high chances
(50-80%) for snowfall totals >6" over the eastern Michigan U.P.. As
the clipper's warm front moves east, sufficient 290K isentropic
ascent and 850-700mb WAA will give rise to snow over the eastern
Great Lakes and northern New England by Tuesday afternoon.
Immediately downwind of Lakes Erie and Ontario, snowfall totals
will generally range between 1-4".


...Northern Plains, Midwest, Great Lakes, & Northeast...
Days 2-3...

By Tuesday morning, a vigorous 500mb shortwave trough with origins
from the large Gulf of AK longwave trough will race towards the
Northern Plains. Given its origins, this "Alberta Clipper" will be
more intense than most clippers. This is because it will have
exceptional synoptic-scale forcing aloft in the form of a roaring
150kt 250mb jet streak, plus anomalous moisture associated with the
strong AR over the Pacific Northwest. By 18Z Tuesday, the
clipper's MSLP looks to be in the mid-upper 980mb range, which
ranks below the 1st climatological percentile for this time of
year. As the storm works its way across the Dakotas Tuesday
morning, impressive 290K isentropic lift and corresponding
850-700mb FGEN will not only help to sustain this potent clipper,
but foster a potent band of snow northeast of the 850mb low track.
There is the potential for an icy wintry mix just along and north
of the surface warm front as a protruding >0C warm nose forces snow
to melt into the form of sleet or freezing rain. But the storm's
fast motion should limit the impacts from freezing rain to around
minor impacts (ice accretions less than a tenth of an inch most
likely).

By Tuesday night, the storm will remain in the mid-980s for
pressure as it races through WI and into MI by Wednesday morning.
WAA out ahead of the storm is likely to cause periods of snow to
envelope the eastern Great Lakes that include areas such as
northwest PA and western NY. From the Northern Plains the the Great
Lakes, not only will snow be problematic for traveling, but gusty
winds are likely to cause blowing and drifting across roads and
cause reduced visibilities. Recent 00Z guidance suite has given
some credence to the EC-AIFS and GFSAI being more on the southern
track of guidance, but there are still a few members that remain a
little farther north. WPC probabilities show a swath of high-chance probabilities (>70%) for snowfall totals >4" from northeast ND on
south and east through the Upper Midwest and the northern half of
Michigan's Mitten. Note that probabilities have increased to
moderate-chance level (40-60%) for totals >6", which is increasing
confidence in a travel-disrupting winter storm on Tuesday.

While the storm's speedy forward motion should help to cap the
chances for more substantial snowfall totals, hourly snowfall rates
of >1"/hr combined with gusty winds will allow for minor to
moderate impacts, some of which will occur during the Monday
evening commute. This is supported by the WSSI-P which depicts high
chances (>70%) for Minor Impacts on Tuesday from northern ND all
the way to northern MI. Residents in the Upper Midwest and Great
Lakes should continue to monitor this storm closely, as should
residents in the Northeast as probabilistic guidance shows
measurable snowfall from this system is possible on Wednesday.

By Wednesday morning, the storm will race into Ontario with strong
850-700mb WAA overrunning a very cold air-mass in the Northeast.
Look for periods of snow to occur from the Central Appalachians on
north through the northern Appalachians. WPC probabilities show moderate-to-high chances (50-70%) for >6" in the Adirondacks, Tug
Hill, the Green and White Mountains. Some valleys in northern New
England have moderate chances (40-60%) for >2" of snowfall before
any issues with mixing or changing to rain occur. As the storm
tracks through the St. Lawrence River Valley, cyclonic flow of the
Great Lakes will spark additional LES bands over the typical snow
belts, including some upslope ascent into the central Appalachians
through early Wednesday morning.


Mullinax/Snell




$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 081948
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
248 PM EST Mon Dec 8 2025

Valid 00Z Tue Dec 09 2025 - 00Z Fri Dec 12 2025


...Pacific Northwest through the Northern High Plains..
Days 1-3...

Prolonged moisture spilling east from a strong atmospheric river
(AR) with multiple embedded waves will spread heavy snow into the
Intermountain West through late-week.

The strong AR will surge onshore the Pacific Northwest this
evening as a shortwave lifts into British Columbia with
impressively confluent and zonal flow pushing into WA/OR. IVT
probabilities for 750 kg/m/s exceed 90% during this time near the
WA/OR border, aided by a powerful Pacific jet streak of over 150
kts moving into British Columbia. This will be the beginning of a
long duration and impressive plume of IVT surging from the Pacific
Northwest and then spilling across the terrain and diving into the
High Plains through late week. While there will be multiple surges
of elevated IVT (and so not a continuous period of heavy
precipitation), in general the entire forecast period will be
unsettled, and IVT exceeding the CFSR climatology is progged via
NAEFS for multiple periods Wednesday and Thursday - indicating the
impressive available moisture associated with this system.

As with most ARs, the forcing and moisture will be attributed to
potent WAA, and this will drive snow levels to well above normal
levels for early December, likely reaching 8000-9000 ft in many
areas west of the Continental Divide and south of a wavering
stationary front/baroclinic boundary that will not only be a
demarcation for colder temperatures, but also provide a surface for
a subtle increase in isentropic ascent and fgen across the region.
Since snow levels south of this front will be so high, any heavy
snow should be confined to only the higher peaks of the northern WA
Cascades, far Northern Rockies, and into NW WY D1-D2 where WPC
probabilities are continuously high (above 70%) for 6+ inches both
days, especially in the northern WA Cascades and higher elevations
surrounding Yellowstone NP.

Then during D3, more significant snowfall becomes probable east of
the Northern Rockies in response to Arctic high pressure sinking
south out of Saskatchewan, driving a cold front to bank into the
terrain from the NE. This will sharpen the baroclinic gradient,
intensifying the resultant fgen, and increase isentropic ascent as
IVT continues to surge eastward beneath the potent Pacific jet
streak arcing to the southeast from British Columbia. While there
is considerable spread still in the placement and coverage of
precipitation D3, confidence is increasing in an axis of heavy snow
spread NW to SE beneath this jet streak and just north of the
front across MT and into the Dakotas. Current WPC probabilities for
more than 6 inches of snow are as high as 70% in the Northern
Rockies near Glacier NP above 7000 ft, with more expansive, but
low-end probabilities (10-30%) for 6+ inches extending well into
the High Plains of MT.


...Northern Plains through the Great Lakes and Northeast...
Days 1-3...

Two distinct fast-moving shortwaves will race across the region
through late-week bringing several rounds of wintry precipitation.

The first of these will stem from a potent vorticity maxima and
associated shortwave trough which will dig out of Manitoba this
evening, reaching Michigan by Tuesday morning, and then crossing
New England to exit into Canada by Wednesday morning. This feature
will remain of modest amplitude and the corresponding downstream
jet streak does not appear well positioned for any enhanced deep
layer ascent to cause cyclogenesis. Despite this, some increased
isentropic ascent from 280K-290K will cause a swath of moderate to
heavy snowfall tonight through Tuesday, with the speed of the
system the primary limiting factor to snowfall. Favorable ascent
into the DGZ will likely yield briefly heavy snow rates,
especially in MN/WI/MI before weakening into New England, with
moderate snow accumulations expected. WPC probabilities for even 2"
of snow are quite limited for this event, but periods of moderate
to briefly heavy snow could create hazardous travel for the monday
commutes for parts of WI, MI, and into Upstate NY.

Immediately in the wake of this first system a second, and likely
more amplified, shortwave and accompanying vorticity lobe, will
swing southeast out of Alberta/Saskatchewan and dive into the
Northern Plains by Tuesday afternoon. This shortwave is progged to
deepen during its progression, and while it should maintain a
positive tilt through its lifetime, it will gain amplitude and dive
farther south than the initial impulse. The resulting impressive
height falls will overlap efficiently with the LFQ of an
impressive Pacific jet streak following in its wake, producing
intense deep layer lift which will help deepen a surface low
/Alberta Clipper/. There is continued spread among the various
deterministic models (generally a global vs. high-res dichotomy) and
their accompanying ensemble spreads, but in general the
differences are small leading to high confidence in a track from
ND Tuesday aftn to lower Michigan Wednesday morning to northern
Maine/Quebec Thursday morning.

In addition to the robust synoptic lift, ascent will become
enhanced through a progressive overlap of 285K-295K moist
isentropic ascent (mixing ratios as high as 4g/kg) with 850-600mb
fgen. This will be well aligned to the most impressive left-exit
diffluence, and directed into the primary snow growth region /DGZ/,
suggesting some banded snow with heavier snow rates occurring N/E
of the low- level circulation. This is reflected by the WPC
prototype snowband tool suggesting at least 1"/hr snowfall rates
diving across the region. While the temporal duration of these snow
rates,owing to the speed of the system, should cap the snowfall
amounts, some secondary banding is possible on the NW side of the
low in response to intensifying deformation, especially Tuesday
night into Wednesday. This may lead to some locally higher snowfall
totals, but at this time, WPC probabilities D1 for 4+ inches of
snowfall reach 50-70% from far eastern ND through much of northern
MN (south of the Arrowhead, however), with a more pronounced stripe
of 50+% probabilities for more than 4 inches on D2 across this same
area and extending into WI and lower MI. The transient nature of
the system will limit the high-end snowfall, but some areas may
receive as much as 8 inches of snowfall.

Additionally, south of this axis of heaviest snow, a transition
zone of mixed precipitation, including freezing rain is expected,
leading to at least modest ice accretion. While light freezing rain
is expected from far eastern MT through lower MI, the greatest
chance (10-30%) for more than 0.1" of icing exists across ND.

As this storm exits the Great Lakes and moves into Ontario D3, the
downstream strong WAA will overrun a very cold antecedent airmass.
This will create a broadening plume of wintry precipitation,
falling primarily as snow from Upstate NY through northern New
England, with some mixing, including periods of freezing rain,
expected farther south into the northern Mid-Atlantic and southern
New England. Total accumulations of wintry precipitation should be
less than areas upstream, but WPC probabilities late D2 into D3 for
4+ inches of snow reach 50-90% for portions of western PA and
across the southern Adirondacks, Greens, Whites, and terrain of
northern ME.

Finally, behind this system a brief period of favorable NW flow
will create lake effect snow (LES) and upslope snow across the
eastern Great Lakes and into the Central Appalachians. While some
of this snow will fall on top of the synoptic snow noted above
(and is included in the snowfall probabilities), and additional 4+
inches of snow has a moderate risk of occurring across the Tug Hill
Plateau and Chautauqua Ridge D3. Similar probabilities for 4+
inches of snow exist in the higher terrain of WV as well where
upslope flow and gusty winds could create hazardous impacts.



Weiss


$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 090828
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 AM EST Tue Dec 9 2025

Valid 12Z Tue Dec 09 2025 - 12Z Fri Dec 12 2025


...Pacific Northwest through the Northern High Plains..
Days 1-3...

Prolonged moisture spilling east from a strong atmospheric river
(AR) with multiple embedded waves will spread heavy snow into the
Intermountain West through late-week.

The strong AR will surge onshore the Pacific Northwest this
evening as a shortwave lifts into British Columbia with
impressively confluent and zonal flow pushing into WA/OR. IVT
probabilities for 750 kg/m/s exceed 90% during this time near the
WA/OR border, aided by a powerful Pacific jet streak of over 150
kts moving into British Columbia. This will be the beginning of a
long duration and impressive plume of IVT surging from the Pacific
Northwest and then spilling across the terrain and diving into the
High Plains through late week. While there will be multiple surges
of elevated IVT (and so not a continuous period of heavy
precipitation), in general the entire forecast period will be
unsettled, and IVT exceeding the CFSR climatology is progged via
NAEFS for multiple periods Wednesday and Thursday - indicating the
impressive available moisture associated with this system.

As with most ARs, the forcing and moisture will be attributed to
potent WAA, and this will drive snow levels to well above normal
levels for early December, likely reaching 8000-9000 ft in many
areas west of the Continental Divide and south of a wavering
stationary front/baroclinic boundary that will not only be a
demarcation for colder temperatures, but also provide a surface for
a subtle increase in isentropic ascent and fgen across the region.
Since snow levels south of this front will be so high, any heavy
snow should be confined to only the higher peaks of the northern WA
Cascades, far Northern Rockies, and into NW WY D1-D2 where WPC
probabilities are continuously high (above 70%) for 6+ inches both
days, especially in the northern WA Cascades and higher elevations
surrounding Yellowstone NP.

Then during D3, more significant snowfall becomes probable east of
the Northern Rockies in response to Arctic high pressure sinking
south out of Saskatchewan, driving a cold front to bank into the
terrain from the NE. This will sharpen the baroclinic gradient,
intensifying the resultant fgen, and increase isentropic ascent as
IVT continues to surge eastward beneath the potent Pacific jet
streak arcing to the southeast from British Columbia. With latest
WSO and WSSI-P guidance now showing >50% probabilities for snowfall
totals surpassing warning criteria and Moderate Impacts, confidence
is increasing in an axis of heavy snow spread NW to SE beneath
this jet streak and just north of the front across MT through D3, and
into the western Dakotas by D4. Current WPC probabilities for more
than 8 inches of snow are as high as 70% in the Northern Rockies
near Glacier NP above 7000 ft, with a larger footprint of
moderate-to-high chances (50-80%) across the heart of Big Sky
Country that includes mountain ranges such as the Little Belt, Big
Snowy, and Absaroka.


...Northern Plains through the Great Lakes and Northeast...
Days 1-3...

Two distinct fast-moving shortwaves will race across the region
through late-week bringing several rounds of wintry precipitation.

The first of these will stem from a potent vorticity maxima and
associated shortwave trough which will dig out of Manitoba this
evening, reaching Michigan this morning, and then crossing New
England to exit into Canada by Wednesday morning. This feature will
remain of modest amplitude and the corresponding downstream jet
streak does not appear well positioned for any enhanced deep layer
ascent to cause cyclogenesis. Despite this, some increased
isentropic ascent from 280K-290K will cause a swath of moderate to
heavy snowfall tonight through Tuesday, with the speed of the
system the primary limiting factor to snowfall. Favorable ascent
into the DGZ will likely yield briefly heavy snow rates, especially
in MN/WI/MI before weakening into New England, with moderate snow
accumulations expected. WPC probabilities for even 2" of snow are
quite limited for this event, but periods of moderate to briefly
heavy snow could create hazardous travel for the monday commutes
for parts of WI, MI, and into Upstate NY.

Immediately in the wake of this first system a second, and likely
more amplified, shortwave and accompanying vorticity lobe, will
swing southeast out of Alberta/Saskatchewan and dive into the
Northern Plains by this afternoon. This shortwave is progged to
deepen during its progression, and while it should maintain a
positive tilt through its lifetime, it will gain amplitude and dive
farther south than the initial impulse. The resulting impressive
height falls will overlap efficiently with the LFQ of an impressive
Pacific jet streak following in its wake, producing intense deep
layer lift which will help deepen a surface low /Alberta Clipper/.
There is continued spread among the various deterministic models
(generally a global vs. high-res dichotomy) and their accompanying
ensemble spreads, but in general the differences are small leading
to high confidence in a track from ND Tuesday aftn to lower
Michigan Wednesday morning to northern Maine/Quebec Thursday
morning.

In addition to the robust synoptic lift, ascent will become
enhanced through a progressive overlap of 285K-295K moist
isentropic ascent (mixing ratios as high as 4g/kg) with 850-600mb
fgen. This will be well aligned to the most impressive left-exit
diffluence, and directed into the primary snow growth region /DGZ/,
suggesting some banded snow with heavier snow rates occurring N/E
of the low- level circulation. This is reflected by the WPC
prototype snowband tool suggesting at least 1"/hr snowfall rates
diving across the region. While the temporal duration of these snow
rates, owing to the speed of the system, should cap the snowfall
amounts, some secondary banding is possible on the NW side of the
low in response to intensifying deformation, especially Tuesday
night into Wednesday. This may lead to some locally higher snowfall
totals, but at this time, WPC probabilities D1 for 4+ inches of
snowfall reach 50-70% from far eastern ND through much of northern
MN (south of the Arrowhead, however), with a more pronounced stripe
of 50+% probabilities for more than 4 inches on D2 across this same
area and extending into WI and lower MI. The transient nature of
the system will limit the high-end snowfall, but some areas locally may
receive around 8 inches of snowfall.

Additionally, south of this axis of heaviest snow, a transition
zone of mixed precipitation, including freezing rain is expected,
leading to at least modest ice accretion. While light freezing rain
is expected from far eastern MT through lower MI, the greatest
chance (10-30%) for more than 0.1" of icing exists across eastern
ND and western MN.

As this storm exits the Great Lakes and moves into Ontario D3, the
downstream strong WAA will overrun a very cold antecedent airmass.
This will create a broadening plume of wintry precipitation,
falling primarily as snow from Upstate NY through northern New
England, with some mixing, including periods of freezing rain,
expected farther south into the northern Mid-Atlantic and southern
New England. Total accumulations of wintry precipitation should be
less than areas upstream, but WPC probabilities early D2 into D3
for 4+ inches of snow reach 50-90% for portions of western PA and
across the southern Adirondacks, Greens, Whites, and terrain of
northern ME.

Finally, behind this system a brief period of favorable NW flow
will create lake effect snow (LES) and upslope snow across the
eastern Great Lakes and into the Central Appalachians. While some
of this snow will fall on top of the synoptic snow noted above
(and is included in the snowfall probabilities), and additional 4+
inches of snow has a moderate risk of occurring across the Chautauqua
Ridge from D2 into D3. Similar probabilities for 4+ inches of snow exist
in the higher terrain of WV as well where upslope flow and gusty winds
could create hazardous impacts. The Tug Hill Plateau, in
particular, has rather high chances (>70%) for snowfall totals
surpassing 8" with even low-to-moderate chances (30-50%) for
snowfall topping 12 inches.


Weiss/Mullinax





$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 092030
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
330 PM EST Tue Dec 9 2025

Valid 00Z Wed Dec 10 2025 - 00Z Sat Dec 13 2025


...Pacific Northwest through the Northern High Plains...
Days 1-3...

Atmospheric River (AR) event to continue through the rest of the
week with heavy rain/snow for the Pacific Northwest into/through
the northern Rockies and western High Plains.

The strong AR will continue this evening/overnight over the
Cascades and push high snow levels into the region from the
southwest, initially from 4000-5000ft over northern WA but rising
to over 7000- 9000ft by early Wednesday as the jet lifts northward
across British Columbia. Any snow at the higher passes will change
to rain even into the higher terrain of NW MT tomorrow with the
strong IVT push (exceeding the 99.5th percentile) as snow levels
rise to 7000ft. Farther southeast, mid-level shortwave will help
yield snow to the higher terrain of WY as well through Wednesday.
For Day 1, WPC probabilities for at least 8 inches of snow are >50%
above 5000- 6000ft over northern areas and above 8000-9000ft over
WY into northern CO.

Into Day 2, upper jet will wobble a bit across southern BC but
keep the Northwest in mild conditions with snow levels 7000-9000ft
to start. Through the day Thursday, ridging over the Northeastern
Pacific may allow snow levels to slip a bit, especially by Thursday
evening as the intense moisture plume subsides a bit. WPC
probabilities for at least 8 inches of snow are >50% above about
6000ft. Much colder air will dive southward east of the Divide
across Montana setting up a significant snowfall by Friday.

By Day 3, ridging will establish itself on a NNW axis from NorCal
into the Northeast Pacific, allowing the moisture plume to lift
northward through BC and also dig southward along/east of the
Divide across much of Montana. At the same time, the strong cold
front will have brought in much colder air to most of the state
east of the Divide, coincident with cold Canadian high pressure
from the north. With a continued moisture surge (albeit less than
earlier in the period but still a quite respectable >90th
percentile PW and IVT), snow will expand and strengthen over
central/eastern MT as snow ratios rise as well. Strong low/mid-
level FGEN may support a heavier axis of snow from central to
southeastern MT but there remains disagreement on the placement as
the upper jet meanders over northeastern MT. For just Day 3 through
00Z Sat, WPC probabilities for at least 6 inches of snow are
highest in areas above 6000ft in the northern Rockies. Over central
to eastern/southeastern MT, WPC probabilities for at least 6
inches of snow are >50% from just east of Great Falls southeastward
through Billings to near the WY border. Snow will continue past
this period as well.


...Upper Midwest through the Great Lakes and Northeast...
Days 1-3...

An amplified shortwave and accompanying vorticity lobe will
quickly dive from the Upper Midwest to across the southern Great
Lakes and into the Northeast through Thursday morning. The
impressive height falls ahead of this wave will overlap efficiently
with the LFQ of a stout Pacific jet streak, producing intense deep
layer lift which will help deepen the resulting surface low. This
surface low / Alberta Clipper will scoot across lower Michigan by
Wednesday morning and northern Maine/Quebec by Thursday morning.
Above normal moisture in conjunction with the impressive dynamics
will lead to a swath of moderate to heavy snowfall along the
surface low track. WPC probabilities for snowfall >4" remains
moderate to high (45-75%) across the heart of WI and central Lower
Michigan, with low probabilities (10-30%) of snowfall >6". South of
the axis of snowfall, a stripe of freezing rain is possible across
portions of southeast MN, northeast IA, southern WI, northern IL,
southern MI, northeast IN and northwest OH, though any ice
accretions will be less than a tenth of an inch.

As this clipper system moves from the Upper Midwest and Great
Lakes and into the Northeast, the downstream strong WAA will
overrun a very cold antecedent airmass. This will create a
broadening plume of wintry precipitation, falling primarily as snow
from Upstate NY through northern New England, with some mixing,
including periods of freezing rain, expected farther south into the
northern Mid- Atlantic and southern New England. Total
accumulations of wintry precipitation should be less than areas
upstream, but WPC probabilities Day 1 into Day 2 for 4+ inches of
snow reach 60-95% for portions of western PA and across the
southern Adirondacks, Greens, Whites, and terrain of northern ME.
Meanwhile, WPC probabilities for freezing rain >0.01" are low to
moderate (30-60%) for the higher terrain of northeast PA and
northwest NJ.

Finally, behind this system a brief period of favorable NW flow
will create lake effect snow (LES) and upslope snow across the
eastern Great Lakes through Day 3. While some of this snow will
fall on top of the synoptic snow noted above (and is included in
the snowfall probabilities), an additional 4+ inches of snow has
moderate to high probabilities (50-95%) downwind of Lake Erie and
especially Lake Ontario. The Tug Hill Plateau, in particular, has
rather high chances (>70%) for snowfall totals surpassing 8" with
even low-to-moderate chances (30-60%) for snowfall topping 12
inches.


...Midwest and Lower Ohio Valley to the Central Appalachians...
Day 3...

A vigorous Clipper system (mid level vort lobe) across the Midwest
Friday morning will pivot through the Lower OH Valley and into the
WV Mountains Friday afternoon and early evening. Overall the model
QPFs (at least the blended means) have come up at 12Z, though
latitudinal differences remain (not surprising given a day 3
forecast). WPC deterministic QPF incorporated a PMM of the latest GFS/ECMWF/NAM/RRFS, which yields a rather elongated footprint of
0.25-0.35" liquid QPF from north-central IL east-southeast through
central IN, southern OH, far northern KY, and essentially the
middle 2/3rds of WV.

Highest QPFs (0.50+ liquid) again were noted across the most
elevated windward slopes in WV, where the westerly upslope is most
favorable. This is also where the latest WPC probabilities of at
least 4" in 24hrs are highest -- currently between 50-70+ percent.
Elsewhere across north-central IL into central portions of IND,
spotty 4"/24hr probabilities between 30-60% were noted.


Fracasso/Miller/Hurley

$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 100825
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
325 AM EST Wed Dec 10 2025

Valid 12Z Wed Dec 10 2025 - 12Z Sat Dec 13 2025


...Pacific Northwest through the Northern High Plains...
Days 1-3...

The atmospheric river (AR) plaguing the Pacific Northwest with
copious amounts of rainfall continues today and into Thursday with
anomalous Pacific moisture coupled with >90th climatological
percentile winds within the 700-200mb layer over WA, northern ID,
and much of MT. Snow levels will be on the rise today, reaching
anywhere from 7,000-9,000ft as the 500-200mb jet core drifts north.
This should begin to force most passes to changeover to rain,
while any lingering snow occurs in the more remote areas of the
Cascades and Lewis Range. The only notable area for heavy snowfall
today is along the >9,000ft peaks of the Absaroka, Tetons, Big
Horns, and Wind River ranges of southern MT and western/northern
WY. WPC probabilities show moderate-to-high chanceS (50-70%) for
snowfall totals >8" through Wednesday night.

Focus turns to Thursday as an Alberta Clipper tracking across
eastern MT helps to usher in an Arctic front from southern Canada.
As the Arctic high builds in from the north, low-level easterlies
will upslope into central and western MT at the same time a ribbon
of 700-300mb moisture streams in overhead. 700mb WAA within W-NW
flow will encounter the Arctic air-mass and result in a band of
700mb FGEN over central MT by Thursday night, resulting in a
quasi-stationary zone of heavy snow over the heart of Big Sky
Country. Heavy snow will linger over the heart of MT through Friday
afternoon before drifting east into eastern MT and the western
Dakotas Friday night. As the band advances east, downsloping winds
and a drying within the 800-500mb layer could cause precipitation
to change over to a wintry mix in central MT, potentially
resulting in a glaze of ice atop fresh snow Friday night.

WPC probabilities moderate-to-high chances (50-80%) for snowfall
totals >8" in central MT with even some low-chance probabilities
10-30%) for isolated totals surpassing 18". The Lewis Range above
5,000ft are likely to receive anywhere between 12-24" of snowfall,
with the remote reaches of the Big Snowy and Little Belt Mountains
potentially exceeding 24". The WSSI-P Moderate probabilities in
central MT are >50% in central and south-central MT, with
Interstates 90, 94, and 87 all at risk of seeing hazardous travel
conditions, with some potential for considerable disruptions and
closures as well. This is depicted in the WSSI-P as well,
indicating 10-20% chances for Major Impacts along portions of these
Interstates Friday and into Saturday morning.


...Great Lakes & Northeast...
Days 1-3...

A shortwave trough responsible for the heavy snow across portions
of the Upper Midwest will strengthen as it tracks through the OH
Valley today. As it does, strong WAA out ahead of the trough will
work in tandem with the left-exit region of a 250-500mb mean
layered left-exit region over the Northeast to produce widespread
precipitation today from the central Appalachians to New England.
An exceptionally cold/dry antecedent air-mass by early December
standards will keep wet-bulb temperatures cold enough to support
snow at the onset across northern PA, the Catskills, Tug Hill,
Adirondacks, Berkshires, and the rest of the New England mountains
through Wednesday afternoon. Farther south, central and eastern
PA, as well as northwest NJ, are likely to see an icy wintry mix
this morning that could result in slick roads, particularly after
following a couple very chilly days where surfaces have been
steadily below freezing. From this "front-end thump" of WAA-driven
and some upslope enhanced snowfall, snowfall totals are likely to
range mostly between 1-4" with the higher totals confined to the
Tug Hill, Adirondacks, Berkshires, Green, and White Mountains where
WPC probabilities show high chances (>70%) for snowfall totals >6"
through Wednesday night.

As low pressure tracks into the St. Lawrence Valley tonight, CAA
within cyclonic flow on the backside of the storm will kick-start
the Lake Effect Snow (LES) machine, as well as supply the central
Appalachians with pronounced upslope snowfall. Precipitation will
fall as snow across the Central Appalachians with lowering snow
levels throughout the day Wednesday and impressive 40-50 kts winds
at 850mb will mix down to cause strong winds within increasing
snowfall rates. This will result in dangerous travel conditions in
the Central Appalachians with whiteout conditions expected above
2,000ft. Snow and winds should gradually taper off Thursday
morning. WPC probabilities show moderate-to-high chances (50-70%)
for snowfall totals >6" with localized low-chance probabilities
(10-30%) for amounts >12". Elsewhere, the LES belts over the
eastern Michigan U.P., northwest section of Michigan's Mitten,
along the Chautauqua Ride, and down wind of Lake Ontario will see
LES bands that stick around these areas through Thursday, with the
band off of Lake Ontario lingering into Friday as well. Through
Friday morning, the Tug Hill Plateau sports high chances (>70%) for
snowfall totals topping 12", with moderate-to-high chances (40-70%)
for >12" amounts along the Chautauqua Ridge through Friday
morning.


...Northern Plains, Midwest, Lower Ohio Valley, & Central
Appalachians...
Days 2-3...

A potent clipper emerging from eastern MT Thursday morning will
race southeast into the heart of the Midwest by Thursday evening.
Healthy 850mb WAA and FGEN to the north and east of the low track
will cause a narrow band of snow light-to-moderate snow from the
eastern Dakotas and southern MN to the nose of IA, and in some
cases a wintry mix across the northern High Plains. The 850mb
FGEN/WAA pivots over the Lower Ohio Valley Thursday night and
reaches the Central Appalachians by early Friday morning. WPC
probabilities show generally lw-to-moderate chances (20-50%) for

4" of snow from central MN on south and east across northern IL,

south-central IN, and southern OH. The highest probabilistic
chances for >4" of snowfall resides in the Potomac Highlands and
central Appalachians of eastern WV and western MD. Here, WNWrly
upslope winds within a 290K isentropic regime and higher SLRs will
provide a favorable environment for locally heavy snowfall. WPC
probabilities show most of the Potomac Highland and central
Appalachians in eastern WV and western MD have moderate-to-high
chances (50-70%) for snowfall totals >4", with some guidance
indicating low chances (10-30%) for localized totals surpassing
10".

There are some members of guidance that depict a chance for light
snowfall across the Mid-Atlantic on Friday, particularly the Blue
Ridge of VA/WV and potentially in the northern VA/northern
MD/southern PA. ECMWF and GFS show weak 700mb Q-vector convergence
over the region with just enough 700-300mb layer saturation to
support a chance for light snow. WPC probabilities show low chances
(10-30%) for >1" snowfall totals across southern and central PA,
northern MD, and northwest VA. While referencing >1" snowfall
potential may seem trivial to mention, recent Mid-Atlantic
snowfall events over the past week has seen snowier trends inside
of 60 hours. It is worth monitoring, but overall snowfall and
travel disruption potential at this time would be light. The WSSI-P
does show 10-20% odds for Minor Impacts across portions of northern
VA and northern MD on Friday.


Mullinax




$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 102035
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 PM EST Wed Dec 10 2025

Valid 00Z Thu Dec 11 2025 - 00Z Sun Dec 14 2025


...Pacific Northwest through the Northern High Plains..
Days 1-3...

The strong Atmospheric River (AR) will start to wane over the
Cascades tonight with the last push of moisture onto the coast. The
upper jet will wobble a bit across southern BC but keep the
Northwest in mild conditions with snow levels 7000-9000ft to start
this evening. Through the day tomorrow, increased ridging over the
Northeastern Pacific will allow snow levels to slip a bit,
especially by Thursday evening as the precipitation intensity
decreases. WPC probabilities for at least 8 inches of snow are >50%
above about 5500ft. Much colder air will dive southward east of the
Divide across Montana setting up a significant snowfall by Friday.

Over the High Plains, warm advection atop a cold surface boundary
layer will support freezing rain from northeastern MT southeastward
through southwestern ND into central SD on Thursday. Model QPF
placement/axis and amounts continue to vary across the region but
trended up with the latest cycle. This introduced some moderate
probabilities (30-60%) of at least 0.10" of icing over north central
SD and northeastern MT/southwestern ND.

By Day 2, ridging will push the moisture plume into British Columbia
but also allow a strong surface cold front to rush southward east of
the Divide. With a continued moisture surge up and around the Pac NW
(albeit less than earlier in the period but still a quite
respectable >90th percentile PW and IVT), snow will expand and
strengthen over central/eastern MT as snow ratios rise as well.
Strong low/mid-level FGEN may support a heavier axis of snow from
central to southeastern MT. Snow will continue into Saturday but
lift northward as the jet wobbles back to the northeast, pushing the
snow into northeastern MT. By Saturday afternoon upper ridging will
finally push inland into the Northwest, yielding drier conditions
for the region. For the day 2-3 period, WPC probabilities of at
least 4 inches of snow are >50% over a large area of Montana east of
the Divide, from just east of Cut Bank through Havre, southward to
Billings, and eastward to southeastern MT/northwestern SD. Within
this region, WPC probabilities for at least 8 inches of snow are

40% across central MT between Havre and Billings.

...Central Appalachians & Northeast...
Day 1...

As low pressure tracks into the St. Lawrence Valley tonight into
Thursday, the focus will shift from synoptically driven snowfall
across northern New England and interior portions of the Northeast
to lake effect snowfall downwind of the Great Lakes. Prior to this
transition, additional snowfall will be most notable across the
Adirondacks, Berkshires, Green, and White Mountains where WPC
probabilities for >6" are moderate to high (60-90%). Additionally, strengthening northwesterly winds oriented perpendicular to the
central Appalachians will also result in significant upslope
snowfall through tonight and into Thursday morning. WPC
probabilities for >4" of snow is moderate to high (50-90%) across
portions of the higher terrain of WV and far western MD with
similar chances for >6".


...Great Lakes...
Days 1-3...

Cold advection within cyclonic flow around the storm system
exiting the Northeast will result in several lake effect snow bands
which are likely to produce multiple rounds of moderate to heavy
snow the next few days. The most prominent bands will develop and
persist along the Chautauqua Ride and across the Tug Hill through
Thursday, with the band off of Lake Ontario lingering into Friday
as well. Lesser bands will also affect the eastern Michigan U.P.
and the northwest section of Michigan's Mitten with WPC
probabilities of total snowfall >4" of 30-70% through Friday.
Meanwhile, the Tug Hill Plateau sports high chances (>70%) for
snowfall totals topping 8", with low to moderate chances (30-60%)
for >12" amounts. Moderate to high chances (40-80%) of >8" also
remain along the Chautauqua Ridge through Friday as well.

By Day 3, a renewed shot of CAA associated with a sharpening trough
and embedded vort max will support additional bands of lake effect
snow downwind of all the Great Lakes, but especially across
portions of the eastern U.P. of Michigan and the northwest portion
of lower Michigan. Here, WPC probabilities for snowfall >4"
increase to 50-90%, with 20-50% probabilities of >8" even outlined
across a small portion of the U.P of Michigan. Low to moderate
probabilities of additional snowfall >4" are also highlighted
downwind of Lake Erie and Lake Ontario.


...Midwest, Ohio Valley, & Central Appalachians...
Day 2...

Emanating from the Northern Rockies/High Plains system, northwest
flow will support a clipper system from the Midwest through the Ohio
Valley into the central Appalachians Thursday afternoon into Friday.
Models continued to struggle with the QPF axis (varying a couple
hundred miles northeast to southwest), with a preference toward the
global and AI models vs the hi-res models. Sufficient moisture
combined with modest forcing beneath the 140kt jet streaks and
within/along a low-level thermal gradient should yield several
inches of snow where SLRs are >12:1. Day 2 WPC probabilities of at
least 4 inches of snow are >30% along an axis from central IL to northern/northeastern KY.


...Corn Belt to the Midwest...
Day 3...

Broad cyclonic flow over Hudson Bay/eastern Canada will carry
another shortwave around its southwestern periphery Friday night
into Saturday from the Plains through the Corn Belt to the Midwest.
This will yield yet another chance of light snow for the region on
the heels of the previous system. WPC probabilities for at least 4
inches of snow on Day 3 are low for now, generally 10-30%, from Iowa
through central IL.


Fracasso/Miller/Mullinax


$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 110840
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 AM EST Thu Dec 11 2025

Valid 12Z Thu Dec 11 2025 - 12Z Sun Dec 14 2025


...Montana...
Days 1-2...

A swath of heavy snowfall is likely tonight into Friday across
much of central and eastern MT. A strong cold front will drop
south today in response to a building mid level ridge off the West
Coast. While considerably weaker than prior days, IVT is still
forecast over the 97th percentile over MT, with PWs around the 90th
percentile. This moisture will override the cold front and result
in a swath of significant snowfall. The latest WPC probabilities
indicate a high chance (greater than 80%) of >4" of snow over much
of central and eastern MT, with portions of the area likely to
exceed 8". This is expected to be more of a prolonged moderate
snowfall with the event picking up in intensity later tonight and
ending late Friday night...although periods of more intense
snowfall rates are likely.

...Great Lakes into Northeast...
Days 1-3...

Cold advection within cyclonic flow around the storm system
exiting the Northeast will result in several lake effect snow bands
today. The most prominent bands will be over the Chautauqua Ridge
and off of Lake Ontario towards Syracuse. WPC probabilities give
both of these areas a greater than 70% chance of an additional 4"+
of snow today into tonight.

On Friday a weak area of low pressure will bring an initial batch
of light WAA snow to the Great lakes, followed by CAA lake effect
snow in its wake. WPC probabilities of exceeding 6" of snow with
this event are over 50% across the lakeshore of the U.P. of
Michigan, northwest lower MI, and the favored areas downwind of
Lake Erie and Ontario. While some areas may locally exceed 8", this
is not expected to be a high end lake effect event given the
relatively short duration of the most favorable ingredients.


...Dakotas, Midwest, Ohio Valley, & Central Appalachians...
Days 1-2...

Northwest flow will support a clipper system moving from the
Northern PLains into the OH Valley today into Friday morning
resulting in a swath of light to moderate snowfall amounts.
Initially we should see a swath of freezing rain this morning from
portions of south central ND into central SD just north of the
shallow cold front, with the latest WPC forecast supporting some
ice accumulations of around or even a bit higher than 0.10".
However as the system quickly moves east today the main
precipitation type will be snow, with perhaps just a bit of a mix
and/or rain on the far southern extent of the precipitation shield.

Even at this short lead time there remains some uncertainty with
the exact axis of highest snowfall with this system. The 00z high
res models remain north of the global guidance, but they did trend
south compared to their 12z runs. The latest WPC preference takes
a consensus approach, resulting in a swath a bit south of the 00z
HREF mean, and a tad north of the global model consensus. The quick
movement of this system will limit snowfall magnitudes, although
the latest WPC probabilities depict a swath of a 30-50% chance of

4" of snow from portions of central IL into south central IN and

towards the KY border. These probabilities could be a bit low, with
these quick hitting clipper systems often verifying with a narrow
band of higher amounts, and a good amount of this snow falling
overnight helping with accumulations. Thus would expect to see a
swath of 4-5" with this system, with a few totals over 5" possible.

The system will begin to weaken as it moves into the Mid-Atlantic,
and thus not expecting much in the way of snow to make it east of
the Appalachians. Even with the weakening nature of the system,
upslope flow will still support accumulating snow over the favored
terrain of WV into southwest VA, with >4" snow probabilities
peaking in the 30-50% range over southeast WV Friday.


...Corn Belt, Midwest, Ohio Valley and Mid-Atlantic...
Day 3...

Another quick moving system will eject into the Northern Plains
Friday night into Saturday, quickly moving across the OH Valley on
Saturday and into the Mid-Atlantic Saturday night into Sunday
morning. This will be a quick moving system which will limit
snowfall magnitudes, however widespread minor impacts can be
expected, with WPC probabilities already indicating a 60-80%
chance of >2" of snow from SD into OH. The probabilities of >4"
drop into the 10-40% range...indicating that totals of this
magnitude are currently unlikely to be widespread, but may very
well occur in localized swaths along the track.

As this system approaches the Appalachians the mid level trough
begins to dig and take on more of a neutral tilt. This will
increase mid and upper level southerly flow and begin the process
of coastal low development. Most likely this trough will remain
too progressive and take on a negative tilt too late to bring a
significant snowfall risk to the Mi-Atanltic and Northeast.
However, it is becoming increasingly likely that we see enough
increase in forcing to see an expansion of some accumulating snow
into the Mid-Atlantic Saturday night.

This expected evolution will support a more prolonged period of
accumulating snowfall into portions of WV and southwest PA, where
probabilities of >4" of snow have increased into the 50-80% range,
with >6" probabilities even over 40%. By later Saturday night model
guidance is trending towards a more favorable solution for a quick
shot of snow even into coastal areas of the Mid-Atlantic. In fact
the 00z deterministic GFS/CMC/ECMWF/AIFS would all bring some
accumulation of snow into the DC to NYC corridor. From an ensemble
perspective, the WSSI-P shows a 50-60% chance of minor impacts
from DC to NYC and a 10-20% chance of Moderate impacts. This
generally seems like a 1-3" event, but the latest guidance does
support the potential for a narrow axis of 3-5" somewhere over the
eastern Mid-Atlantic. This is a lower probability outcome and
likely the ceiling for this event given the quick storm motion, but
the risk is supported by the aforementioned low WSSI-P moderate
probabilities and some low >4"+ WPC probabilities. These quick
northwest flow systems are tricky to pin down with much lead time,
so future adjustments to the forecast are likely.

Chenard


$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 111951
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
251 PM EST Thu Dec 11 2025

Valid 00Z Fri Dec 12 2025 - 00Z Mon Dec 15 2025


...Montana...
Days 1-2...

A second round of heavy snowfall (although with minimal break from
the first) will develop across MT, generally east of the
Continental Divide and expand into the High Plains. This will be
the result of overlapping ascent slowly shifting northeast with
time into a cold and anomalously moist environment.

The event begins to expand as a powerful (150+ kt) Pacific jet
streak begins to pivot northeast, while a strong cold front
continues to waver NW to SE and bank into the terrain. The overlap
of this jet and its accompanying IVT (still > 90% probability of
exceeding 250 kg/m/s spilling east of the terrain) will help expand precipitation once again across the area. This will fall
exclusively as snow thanks to rapid column cooling behind the
front. The accompanying westerly flow aloft, while not ideal for
column moistening, will lead to at least modest isentropic ascent
atop the cold front, primarily along the 290K-295K surfaces,
helping to expand the snow swath. At the same time, persistent
700-600mb fgen will drift across the area, aided by the entrance
region to the upper jet, and driving ascent efficiently into the
deepening DGZ (30% probability from the SREF for DGZ depth
exceeding 100mb) suggest the potential for periods of heavy
snowfall rates exceeding 1"/hr (up to 70% chance Friday evening).

Temperatures will be quite cold, so SLRs are expected to be fluffy
and above-climo which should result in rapid accumulation of
snowfall. This will be most pronounced where any jet-enhanced
banding can occur, especially due to the prolonged and nearly-
stationary nature of the upper jet aloft. This is reflected by WPC probabilities that support a moderate risk (50-90%) for at least 6
inches of snow across central MT just east of the terrain, with
locally as much as 12" possible (10-30%), and locally higher
amounts in the mountains.


...Great Lakes into Northeast...
Days 1-3...

Persistent troughing across the east will keep cyclonic flow in
place across the Great Lakes and into the Northeast through the
weekend, while periodic shortwave impulses rotate southeast through
the flow. Each of these shortwaves will result in transient
enhanced ascent, with the most impressive height falls likely D3 as
the last in this series of shortwaves amplifies sharply late in the
forecast period.

The result of this evolution will be periods of light synoptic snow
associated with each shortwave, followed by more impressive lake
effect snow (LES) or lake-enhanced snow. While many areas will
likely experience at least light synoptic snow, any significant
accumulations are expected to be confined to lake effect snow areas
on the persistent W/NW flow, with enhancement occurring behind
each shortwave and the accompanying CAA. On D1, modest LES, which
has a WPC probability of 10-30% for exceeding 4" is confined to the
Keweenaw Peninsula of MI and just east of Lake Ontario.

However, during D2 and D3, LES becomes more widespread and
intense. With 850mb temps crashing to potentially less than -20C
over the lake temperatures that are still generally +2C to +8C will
create deep inversion depths and impressive lake-induced
instability to support heavy LES. Snowfall rates of at least 2"/hr
appear probable, especially across the U.P. and then east of Lakes
Erie/Ontario where upstream connection may additionally occur. WPC probabilities D2 for 4+ inches of snow are above 50% across much of
the southern shore of Lake Superior in the U.P., as well as near
Buffalo, NY and into the Tug Hill Plateau. By D3, these
probabilities expand to include the NW and SW L.P. of MI as well as
the breadth of the Chautauqua Ridge. 2-day snowfall totals from the
LES (D2-D3) could 18" in some areas.

...Northern Plains through the Ohio Valley...
Days 1-3...

Pinched cyclonic flow on the periphery of an amplifying trough over
southeast Canada will keep flow progressive from the Northern
Plains through the Ohio Valley, while dual potent shortwave troughs
rotate through the flow.

The first of these will be accompanied by a strung out lobe of
vorticity racing from South Dakota early D1 to the Mid-Atlantic
Coast early D2. The speed of this system will somewhat limit the
potential for heavy precipitation. However, forcing for ascent will
maximize on the periphery of a potent upper jet streak digging
southeast coincident with a narrow corridor of impressive 290K
isentropic ascent and 925-700mb fgen. The most intense ascent is
expected from Iowa into Kentucky where a band of heavy snowfall is
likely to translate southeast on the edge of the strongest WAA.
This will create a stripe of moderate snowfall with briefly heavy
snow rates exceeding 1"/hr possible (30% chance). WPC probabilities
for this lead shortwave reach 30-50% for 4+ inches, with locally
6+" possible (10-30%) in IL/IN.

Immediately following this first wave will be a second shortwave
with more impressive amplitude, leading to a second streak of
moderate to heavy snowfall crossing almost the identical path.
Although there is considerable latitudinal spread among the
guidance, it is probable that the lead shortwave will push the
baroclinic gradient south to support a slight southward push of
heavy snow with the next wave, at least until amplification of the
mid-level pattern occurs Saturday evening which could result in the
heaviest axis again moving across central IN and then into the
lower Ohio Valley. Another stripe of moderate to heavy snow is
likely despite the transient nature of the event as the DGZ remains
elevated and 700-600mb fgen increases which crosses directly into
the DGZ to produce ample snow growth potential. Regional soundings
across this area also indicate a near-isothermal layer beneath the
DGZ, and while temperatures are cold, should still support fluffy
SLR with efficient accumulations. At this time, WPC probabilities
on D2 indicate a 30-50% chance of an additional 4+ inches in
central IL, reaching 30-70% D3 from IN through southern OH.

Although there will be a break between these two events, some areas
could receive double-digit snowfall by the time both of these
events are over, and with cold temperatures in place, this will
likely create hazardous travel for the region.


...Central Appalachians and Mid-Atlantic...
Days 1-3...

The same impulses/clippers bringing snow to the Plains/Midwest will
track E/SE into the Central Appalachians and Mid-Atlantic states.
The first of these will be exiting the coast Friday morning, and
while snow will generally be modest, the addition of upslope flow
on W/NW winds into the Central Appalachians will result in moderate accumulations across the terrain of WV. Here, WPC probabilities D1
into D2 support a low risk (10-30+%) of at least 4 inches of
snowfall.

The more significant event is with the secondary impulse which will
be intensifying D3 as the mid-level pattern amplifies and swings
the primary trough axis into the Central Appalachians and Mid-
Atlantic Sunday morning. This will drive rapid height falls into
the area, while the sharpening trough axis will help arc the
downstream jet streak poleward to produce rapidly intensifying
upper diffluence within the RRQ. Westerly mid-level flow will cause
impressive upslope flow into the terrain of WV/MD/PA once again,
but in this cause the available moisture will be more significant,
which when added to the robust deep layer ascent results in WPC
probabilities that exceed 50% for 6+ inches from the Laurel
Highlands through central WV, with locally more than 10 inches
possible.

The more challenging aspect of this forecast is what happens across
the coastal Mid-Atlantic states, including the I-95 corridor. As
the upper jet intensifies and arcs, it will likely provide enough
ascent downstream of the sharpening trough to produce a secondary
axis of moderate to heavy snow in the vicinity of I-95. The speed
at which this trough deepens and the corresponding jet amplifies
will drive the position of the heavy snow axis, which remains quite
uncertain at this time. However, with the PV anomaly swinging east
and potentially pushing the 1.5 PVU surface down below 450mb, this
could be a briefly intense event downstream.

Evaluation of the recent cluster analysis indicates that the
primary EOF /uncertainty/ revolves around the speed of this trough amplification, and there is quite a bit of spread among the various
clusters. In general, the EC members are bit slower and deeper,
while the GEFS members are a little faster and weaker. Somewhere in
the middle is probably reasonable at this time, which results in a
stripe of heavy snow that will develop within increasing 850-700mb
fgen somewhere near I-95 from Washington, D.C. through NYC and
into Cape Cod, MA. There is still a lot of spread, but where this
band develops, which is currently expected near I-95, WPC
probabilities are moderate (50-70%) for at least 2 inches of snow
between DC and NYC, with locally more than 4 inches possible.
Considerable adjustments to the location of this band are still
possible, so further refinements to the location and accompanying
probabilities can be expected in the next few forecast cycles.

Weiss


$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 112224
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
524 PM EST Thu Dec 11 2025

Valid 00Z Fri Dec 12 2025 - 00Z Mon Dec 15 2025


...Montana...
Days 1-2...

A second round of heavy snowfall (although with minimal break from
the first) will develop across MT, generally east of the
Continental Divide and expand into the High Plains. This will be
the result of overlapping ascent slowly shifting northeast with
time into a cold and anomalously moist environment.

The event begins to expand as a powerful (150+ kt) Pacific jet
streak begins to pivot northeast, while a strong cold front
continues to waver NW to SE and bank into the terrain. The overlap
of this jet and its accompanying IVT (still > 90% probability of
exceeding 250 kg/m/s spilling east of the terrain) will help expand precipitation once again across the area. This will fall
exclusively as snow thanks to rapid column cooling behind the
front. The accompanying westerly flow aloft, while not ideal for
column moistening, will lead to at least modest isentropic ascent
atop the cold front, primarily along the 290K-295K surfaces,=20
helping to expand the snow swath. At the same time, persistent
700-600mb fgen will drift across the area, aided by the entrance
region to the upper jet, and driving ascent efficiently into the
deepening DGZ (30% probability from the SREF for DGZ depth=20
exceeding 100mb) suggest the potential for periods of heavy=20
snowfall rates exceeding 1"/hr (up to 70% chance Friday evening).=20

Temperatures will be quite cold, so SLRs are expected to be fluffy
and above-climo which should result in rapid accumulation of
snowfall. This will be most pronounced where any jet-enhanced
banding can occur, especially due to the prolonged and nearly-
stationary nature of the upper jet aloft. This is reflected by WPC probabilities that support a moderate risk (50-90%) for at least 6
inches of snow across central MT just east of the terrain, with
locally as much as 12" possible (10-30%), and locally higher
amounts in the mountains.


...Great Lakes into Northeast...
Days 1-3...

Persistent troughing across the east will keep cyclonic flow in
place across the Great Lakes and into the Northeast through the
weekend, while periodic shortwave impulses rotate southeast through
the flow. Each of these shortwaves will result in transient
enhanced ascent, with the most impressive height falls likely D3 as
the last in this series of shortwaves amplifies sharply late in the
forecast period.

The result of this evolution will be periods of light synoptic snow
associated with each shortwave, followed by more impressive lake=20
effect snow (LES) or lake-enhanced snow. While many areas will
likely experience at least light synoptic snow, any significant
accumulations are expected to be confined to lake effect snow areas
on the persistent W/NW flow, with enhancement occurring behind
each shortwave and the accompanying CAA. On D1, modest LES, which
has a WPC probability of 10-30% for exceeding 4" is confined to the
Keweenaw Peninsula of MI and just east of Lake Ontario.=20

However, during D2 and D3, LES becomes more widespread and=20
intense. With 850mb temps crashing to potentially less than -20C
over the lake temperatures that are still generally +2C to +8C will
create deep inversion depths and impressive lake-induced
instability to support heavy LES. Snowfall rates of at least 2"/hr
appear probable, especially across the U.P. and then east of Lakes
Erie/Ontario where upstream connection may additionally occur. WPC probabilities D2 for 4+ inches of snow are above 50% across much of
the southern shore of Lake Superior in the U.P., as well as near
Buffalo, NY and into the Tug Hill Plateau. By D3, these
probabilities expand to include the NW and SW L.P. of MI as well as
the breadth of the Chautauqua Ridge. 2-day snowfall totals from the
LES (D2-D3) could 18" in some areas.


...Northern Plains through the Ohio Valley...=20
Days 1-3...

Pinched cyclonic flow on the periphery of an amplifying trough over
southeast Canada will keep flow progressive from the Northern
Plains through the Ohio Valley, while dual potent shortwave troughs
rotate through the flow.=20

The first of these will be accompanied by a strung out lobe of
vorticity racing from South Dakota early D1 to the Mid-Atlantic
Coast early D2. The speed of this system will somewhat limit the
potential for heavy precipitation. However, forcing for ascent will
maximize on the periphery of a potent upper jet streak digging
southeast coincident with a narrow corridor of impressive 290K
isentropic ascent and 925-700mb fgen. The most intense ascent is
expected from Iowa into Kentucky where a band of heavy snowfall is
likely to translate southeast on the edge of the strongest WAA.
This will create a stripe of moderate snowfall with briefly heavy
snow rates exceeding 1"/hr possible (30% chance). WPC probabilities
for this lead shortwave reach 30-50% for 4+ inches, with locally
6+" possible (10-30%) in IL/IN.

Immediately following this first wave will be a second shortwave
with more impressive amplitude, leading to a second streak of
moderate to heavy snowfall crossing almost the identical path.
Although there is considerable latitudinal spread among the
guidance, it is probable that the lead shortwave will push the
baroclinic gradient south to support a slight southward push of
heavy snow with the next wave, at least until amplification of the
mid-level pattern occurs Saturday evening which could result in the
heaviest axis again moving across central IN and then into the
lower Ohio Valley. Another stripe of moderate to heavy snow is
likely despite the transient nature of the event as the DGZ remains
elevated and 700-600mb fgen increases which crosses directly into
the DGZ to produce ample snow growth potential. Regional soundings
across this area also indicate a near-isothermal layer beneath the
DGZ, and while temperatures are cold, should still support fluffy
SLR with efficient accumulations. At this time, WPC probabilities
on D2 indicate a 30-50% chance of an additional 4+ inches in
central IL, reaching 30-70% D3 from IN through southern OH.=20

Although there will be a break between these two events, some areas
could receive double-digit snowfall by the time both of these
events are over, and with cold temperatures in place, this will
likely create hazardous travel for the region.


...Central Appalachians and Mid-Atlantic...
Days 1-3...

The same impulses/clippers bringing snow to the Plains/Midwest will
track E/SE into the Central Appalachians and Mid-Atlantic states.
The first of these will be exiting the coast Friday morning, and
while snow will generally be modest, the addition of upslope flow
on W/NW winds into the Central Appalachians will result in moderate accumulations across the terrain of WV. Here, WPC probabilities D1
into D2 support a low risk (10-30+%) of at least 4 inches of
snowfall.

The more significant event is with the secondary impulse which will
be intensifying D3 as the mid-level pattern amplifies and swings
the primary trough axis into the Central Appalachians and Mid-
Atlantic Sunday morning. This will drive rapid height falls into=20
the area, while the sharpening trough axis will help arc the
downstream jet streak poleward to produce rapidly intensifying
upper diffluence within the RRQ. Westerly mid-level flow will cause
impressive upslope flow into the terrain of WV/MD/PA once again,
but in this cause the available moisture will be more significant,
which when added to the robust deep layer ascent results in WPC
probabilities that exceed 50% for 6+ inches from the Laurel
Highlands through central WV, with locally more than 10 inches
possible.

The more challenging aspect of this forecast is what happens across
the coastal Mid-Atlantic states, including the I-95 corridor. As
the upper jet intensifies and arcs, it will likely provide enough
ascent downstream of the sharpening trough to produce a secondary
axis of moderate to heavy snow in the vicinity of I-95. The speed
at which this trough deepens and the corresponding jet amplifies
will drive the position of the heavy snow axis, which remains quite
uncertain at this time. However, with the PV anomaly swinging east
and potentially pushing the 1.5 PVU surface down below 450mb, this
could be a briefly intense event downstream.

Evaluation of the recent cluster analysis indicates that the=20
primary EOF /uncertainty/ revolves around the speed of this trough=20 amplification, and there is quite a bit of spread among the various
clusters. In general, the EC members are bit slower and deeper,=20
while the GEFS members are a little faster and weaker. Somewhere in
the middle is probably reasonable at this time, which results in a
stripe of heavy snow that will develop within increasing 850-700mb
fgen somewhere near I-95 from Washington, D.C. through NYC and=20
into Cape Cod, MA. There is still a lot of spread, but where this=20
band develops, which is currently expected near I-95, WPC
probabilities are moderate (50-70%) for at least 2 inches of snow
between DC and NYC, with locally more than 4 inches possible.
Considerable adjustments to the location of this band are still
possible, so further refinements to the location and accompanying
probabilities can be expected in the next few forecast cycles.

Weiss



...Extreme Cold Messages are in effect. Please see current Key=20
Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!7oKQMthO_AgvWGJsUC1TmBbPapSWjWECK-1YZ5cN-q80V= kFeTBweceqBKIk5Gax1GIyogCRFY1qpHApLNATHY68k4h0$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 120908
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
408 AM EST Fri Dec 12 2025

Valid 12Z Fri Dec 12 2025 - 12Z Mon Dec 15 2025


...Montana...
Day 1...

NWly jet downstream of an amplifying ridge axis off the PacNW coast
continues to intensify through this morning with 250mb winds
increasing above 150kt over south-central Alberta. Pacific moisture
continues to shift inland south of this jet which meets
particularly cold air from the Canadian Prairies that is banking=20
up against the eastern slopes of the MT Rockies. The amplifying=20
ridge maintains the jet dynamics with banding over central MT now=20
expected to drift north to northern MT through this evening before=20
ejecting southeast over the north-central Plains late=20
tonight/Saturday morning.=20

Ongoing freezing rain along the southern periphery of the banding
in valleys in the eastern slopes will continue this morning with
only a narrow strip of wintry mix shifting north with the southern
extension rest of today. Otherwise this is fluffy with consistent
0.5"/hr rates across the MT Plains through this evening (per 00Z
HREF) with SLR in the 15 to 18:1 range. Day 1 PWPF for >6" snow is
over 40% across much of north-central to eastern MT, including=20
around Havre where probabilities are above 70%.=20


...Northern Plains through the Midwest to the central=20
Appalachians... Days 1-2...

A reinforcing trough over the Gulf of Alaska early this morning
rides an increasing NWly jet today, reaching southern Saskatchewan
tonight. This trough is the catalyst for allowing ongoing snow
banding over MT to eject southeast across the Dakotas late tonight
and the Midwest Saturday. Strong jet dynamics and ample cold air
with Arctic origin allows for decent snow rates through this swath, consistently over 0.5"/hr per the 00Z HREF. Day 1.5 PWPF for >4"
are lower over South Dakota where the bands are fairly progressive,
generally 30%, but higher over Iowa through north-central IL and
central IN where the band pivots east with values of 40-60%.
Probabilities continue to ramp up to the east over Ohio later
Saturday before orographic lift brings increasing probabilities=20
for >6" to northern WV, peaking for areas just west of the
Allegheny Front where Day 2 PWPF for >6" are 40-70%.=20

This swath is forecast to be a bit north of the current snow
tracking east from southern IN and eastern KY. These two
clippers will produce decent swaths of snow and combine to cover
large areas of the Midwest with snow through Saturday.=20


...Mid-Atlantic through the coastal Northeast...=20
Days 2-3...

The Saturday shortwave trough/clipper amplifies an upper low over
Lake Superior Saturday allowing it to further develop and dig
south over the eastern Great Lakes Saturday night. The surface
component of this low develops as a trough off the Mid-Atlantic
coast to the Outer Banks by 12Z Sunday. Right entrance jet dynamics
and this developing surface trough allow moderate to locally heavy
banding to develop over the central/northern Mid-Atlantic through
southern New England Saturday night into Sunday. Placement of
banding with a key area of 0.25" QPF remains a bit uncertain at
this time, but areas from Baltimore through New Jersey and=20
possible Long Island are of most concern now. Day 2.5 PWPF for >4"=20
are 30-40% around Philly and around 20% over southern Connecticut=20
through southeast Mass. Confidence has increased on the snow=20
advancing and reaching the NYC metro late Saturday evening.=20

Rapid low pressure development is expected off the Northeast coast
Sunday which will maintain offshore flow and should allow ocean/bay
enhanced snow for the Cape and Islands through Sunday night. Day 3
PWPF for >4" are around 30% for Cape Cod.


...Great Lakes...=20
Days 1-3...

Persistent troughing across the east will maintain cold conditions
as a storm brings another round of lake enhanced and effect snow=20
across the Great Lakes tonight through Sunday. Low pressure=20
currently over Manitoba dives southeast to Lake Superior tonight=20
before amplifying by an aforementioned shortwave trough. Westerly=20
flow ahead of this low brings synoptic snow with lake enhancements=20
for the U.P. and tip of the L.P. mitt where Day 1.5 PWPF for >6"=20
are 30-50%.=20

This westerly flow then crosses the eastern Great Lakes early
Saturday bringing renewed cold air advection and transient single-
banding to snow belts east of Cleveland through the Chautauqua
Ridge and across the Tug Hill where Day 2 PWPF for >6" are 40-70%.
LES then continues on NWly flow behind the low on Sunday with Day 3
PWPF for >4" 40-80% in northwest PA and around Syracuse.=20



Jackson



...Extreme Cold Key Messages are in effect and linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!47yZ9O3RTM9AE6Rtm8R9BQEbLvVg3byGcA07p9m73MzIA= 1eUO2G1MfH3v-DCGZA6hRJFaFZPvnR-6NLsfgEM7HTLZE8$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 121847
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
147 PM EST Fri Dec 12 2025

Valid 00Z Sat Dec 13 2025 - 00Z Tue Dec 16 2025


...Montana...
Day 1...

The ongoing strong upper jet streak angled NW to SE will continue
tonight and into early Saturday, while westerly mid-level flow
isentropically ascends the baroclinic gradient left from a cold
front banked against the Continental Divide. This will result in=20
persistent moderate snowfall with rates 0.5"/hr to 1"/hr at times=20
across central MT. The heaviest snowfall should taper off quickly=20
late tonight with snow ending by Saturday morning in response to=20
the strongest ascent pivoting east away from the area. The=20
continuing snowfall should remain fluffy with high SLRs thanks to a
very cold column, so additional accumulations exceeding 4 inches=20
are likely (>70% chance) in central MT, with local additional=20
snowfall as much as 8 inches possible (10% chance) in a few areas.


...Northern Plains through the Ohio Valley into the Central=20 Appalachians...=20
Days 1-2...

A closed 500mb low dropping along the Ontario/Great Lakes border
will be the catalyst for another fast moving clipper-type low=20
racing from the Northern Plains to the Ohio Valley D1, and then=20
exiting the Mid-Atlantic coast D2. The primary driver of this=20
clipper is expected to be a secondary impulse/vorticity lobe=20
swinging through the pinched flow, to combine with the persistent=20
and intense upper jet streak aloft driving deep layer ascent. While
the temporal duration of any lift will be modest due to the=20
progressive nature of the system, the overlap of height falls with=20 intensifying fgen (both through WAA and the result of the upper jet
streak position) will be sufficient to drive robust omega through=20
the snow growth zone. With strong lift occurring into a DGZ that is
deepening in the cold airmass, periods of heavy snow are likely,=20
especially within a narrow translating band from eastern SD through
IN on D1, and then continuing into OH D2 before running into the=20
terrain of WV and wringing out the remaining moisture via upslope=20 enhancement before Saturday night.

WPC probabilities for snow exceeding 4" reaches 10-30% from eastern
SD through central IN, but contains a local maxima above 50% in
central IL/IN where the best overlap of ascent into the deepening
DGZ occurs. This could support snowfall rates above 1"/hr at times
leading to local maxima above 6" (10% chance). During D2 the
heaviest snowfall axis shifts eastward, with a 50-90% chance of
more than 4 inches occurring across southern OH and into the
terrain from the Laurel Highlands of PA through central WV. The
greatest snowfall, which may reach 10" in local spots, is expected
in the higher terrain of WV.


...Mid-Atlantic through Southern New England...=20
Day 2...

Extremely challenging forecast for Sunday as a system develops east
of the Mid-Atlantic Sunday morning and then skirts off into the
Atlantic Ocean. The primary mechanism for this system will be the
upstream shortwave racing across the Midwest. As this feature moves
east, it will amplify rapidly into a sharpening trough, but still
maintain a positive tilt. Downstream of this trough, especially 06Z
to 18Z Sunday, rapid height falls will occur through the Mid-
Atlantic states and into southern New England, concurrent with a
rapid amplification of a jet streak which peak above 150 kts in New
England while arcing more poleward. This will place the favorable
RRQ for diffluent ascent directly beneath the strongest height
falls, and the accompanying (albeit modest) fgen due to WAA will
merge with the resulting fgen from the jet streak to drive a period
of rapidly intensifying deep layer ascent. The guidance continues
to suggest that the strongest lift will occur directly into the
DGZ, so despite marginal thermals at onset (especially across the
Mid-Atlantic) precipitation will become increasingly all-snow, and
may be heavy at times as banded snow develops and pivots northeast.=20

This event should last no more than 12 hours in any given location,
and the exact placement, timing, and intensity of the jet streak
will create the important differences in snowfall placement and
amounts. While guidance continues to feature some differences,
there has been a reduction in spread this aftn which is reflected
by increasing probabilities for accumulating snowfall, especially
along the I-95 corridor from Washington, D.C. to NYC. At this time,
WPC probabilities suggest a 30-70% chance of at least 2 inches from
Washington to NY and onto Cape Cod, with the greatest potential for
4+ inches occurring from near Philadelphia through central Long
Island. While this will occur early Sunday morning, at least=20
briefly heavy snowfall rates will make for hazardous travel.


...Great Lakes...=20
Days 1-3...

Persistent troughing across the east will maintain cold=20
conditions, with multiple shortwaves and accompanying cold front
driving renewed CAA for lake effect snow (LES) with modest synoptic
snow also accompanying each impulse. These impulses are most likely
to cross the region on Saturday, with another impulse on Monday.
While the accompanying synoptic/WAA snow is likely to produce only
modest accumulations, the post-frontal CAA will cause 850mb temps=20
to drop to as low as -20C to -25C Sat/Sun, with more tempered cold=20
of around -10C Monday. While the heaviest LES is expected
Saturday/Sunday as inversion depths over the lakes climb towards
10,000 ft, significant LES is also likely Monday despite the weaker
overall ascent/lake-induced instability.

WPC probabilities D1 and D2 are elevated, and feature a moderate
risk (30-70% chance) of exceeding 6 inches both days across the
southern shore of Lake Superior in the U.P. of MI, as well as
portions of NW L.P. near Traverse City, and across the Tug Hill
Plateau east of Lake Ontario. Slightly lower probabilities exist
along the Chautauqua Ridge. Snow totals of 1-2 feet are possible in
these areas as well. Then during D3 the flow becomes more westerly
focusing the heaviest LES across the Chautauqua Ridge and Tug Hill
Plateau where WPC probabilities indicate a high chance (>70%) for
additional snowfall of 6+ inches.

Weiss


...Extreme Cold Key Messages are in effect. Please see current Key
Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-R0uB7_t2x6rqwmMIRkN23YJYqdVbS_8eeqYB5LOVq_UD= 5EiK3VDt10MQf31TpTfsOgP5R_0a9gVXeYjJXS3kl7W9zQ$=20


$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 130906
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
406 AM EST Sat Dec 13 2025

Valid 12Z Sat Dec 13 2025 - 12Z Tue Dec 16 2025


...North-Central Plains, Midwest to the Central Appalachians...=20
Day 1...

Low to mid-level low is over north shore of Lake Superior with a
reinforcing shortwave trough over far northeast MT. This wave is
riding a powerful 140kt jet that extends across the Midwest and
through the Mid- Atlantic. Intensifying fgen (both through WAA and
the result of the upper jet streak position) will be sufficient to
drive omega through the snow growth zone through this evening.=20
With strong lift occurring into a DGZ that is deepening in the cold
airmass, periods of heavy snow are expected, especially within a=20
narrow translating band from Iowa through Ohio and northern WV
today. Forcing is strong enough to warrant a risk for thundersnow=20 particularly midday/early afternoon over central IL/IN where 1"/hr
rates are possible per the 00Z HREF.=20
The bands rise over the Allegheny Plateau this evening where
orography once again brings a risk for 1"/hr rates. Day 1 PWPF for

6" are around 10% in central IL/IN and quickly increase from 40%

to 70% across far southeast OH through north-central WV. Snow rates
drop off Sunday morning over the central Appalachians, but the
upper trough does cross midday, so continued upslope snow showers
can be expected at least through the day light hours.


...Mid-Atlantic through Southern New England...=20
Days 1/2...

Upper low stalls over northern Lake Superior today before ejecting
southeast tonight with the aid of a reinforcing shortwave. The
resultant upper trough axis reaches the Northeastern Seaboard
Sunday evening with downstream surface trough then low development
off the Mid-Atlantic coast Sunday morning. Right entrance dynamics
aid fgen banding to develop in the lee of the central Apps later
this evening, most likely over north-central MD east through NJ
before the surface trough/low offshore provides additional forcing
for more intense banding overnight to shift south and east. This=20
system is fairly progressive, but the frontal forcing in
increasingly cold air allows 0.75"/hr rates in the Mid-Atlantic,
extending to southern New England early Sunday. Marginal thermals=20
at the southern extend of the precip swath to begin with quickly=20
shift to all snow - this is aided the nighttime occurrence.=20

This event should last no more than 12 hours in any given location,
and the exact placement, timing, and intensity of the jet streak
and offshore trough will determine where the heavier bands setup
and pivot. Day 1.5 PWPF for >6" are over 10% from just north of DC
through Cape Co with a peak of around 30% for greater Philly.=20


...Great Lakes...=20
Days 1-3...

Aforementioned low pressure system stalling over Lake Superior
today ejects southeast tonight with a reinforcing shortwave trough
passage on Monday. Subterranean DGZ under the low today makes for
coarse/low SLR snow, but some warming this evening brings back the
dendrites and 20:1 SLRs to the U.P.

Day 1 PWPF for >6" are 40-80% over NWly flow snow belts in the=20
eastern U.P. and east of Grand Traverse Bay. Wly flow snow belts
east of Lakes Erie/Ontario result in Day 1 PWPF >6" of 30-50% east
of Cleveland to the Chautauqua Ridge and over 80% for the Tug Hill
where single banding LES sets up this evening. Lull expected
for Sunday night as low level ridging shifts east of the Lakes. But
then shortwave crosses Monday with a decent, but transient swath of
lake enhanced snow. Light to locally moderate synoptically driven
snow across the Great Lakes region Monday with more single banding
in westerly flow over Lake Ontario into the Tug Hill where Day 3
PWPF for >6" is over 80%.=20


...Pacific Northwest...
Days 2/3...

Potent atmospheric river arrives Monday morning to western WA/OR
with snow levels skyrocketing up to 9000ft over the Cascades. A
shortwave trough passage over WA late Monday brings snow levels on
the North Cascades down to 5000ft, reaching 4000ft on Tuesday.
Lower precip rates are expected behind the trough passage, but
moderate snow brings Day 3 PWPF for >6" in the 40-60% range in the
high northern WA Cascades.=20


The probability of significant icing is less than 10 percent.=20

Jackson



...Extreme Cold Key Messages are in effect and linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!_jPxnzcgK9JB0jlxCEYkNgPmBqDB9AV_xArz815tBmqPn= UJySnOPdk6IfueYnBtMZQh3ZGrHh9pNlUcp8ywHHzAOYSE$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 132003
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
303 PM EST Sat Dec 13 2025

Valid 00Z Sun Dec 14 2025 - 00Z Wed Dec 17 2025


...Upper Ohio Valley to Central Appalachians...
Days 1-2...

Moderate to heavy snow will be ongoing at the start of the forecast
period (00z Sun) across the Ohio Valley into the central
Appalachians with upslope snow continuing along the higher terrain
through Monday morning. A mid- level low associated with this=20
snowfall is over northeast shore of Lake Superior with a=20
reinforcing shortwave trough over the Upper Midwest. This wave is=20
riding a powerful 140kt jet that extends across the Midwest and=20
through the Mid- Atlantic. Intensifying 700 mb fgen (both through=20
WAA and the result of the upper jet streak position) will be=20
sufficient to drive omega through a wide (greater than 100 mb) snow
growth zone through this evening. With strong lift occurring into=20
a DGZ that is deepening in the cold airmass, periods of heavy snow=20
and high snow ratios (around 20:1) are expected, especially within=20
a narrow translating band from Ohio into northern WV today,=20
southwest PA and far western MD tonight.
=20
The bands rise over the Allegheny Plateau this evening where
orography brings a risk for 1"/hr rates. Following this system a=20
strong arctic cold front pushes southward and promotes lake=20
enhanced upslope flow into the high elevations of southwest PA,=20
western MD, and WV. Day 1 PWPF for >6" are around 40% to 70% across
north- central WV into western MD and southwest PA.


...Mid-Atlantic through Southern New England...=20
Day 1...

The same system impacting the Ohio Valley shifts towards the Mid-
Atlantic and Northeast tonight as the upper low stalls over=20
northern Lake Superior before ejecting southeast with the aid of a
reinforcing shortwave. The resultant upper trough axis reaches the
Northeastern Seaboard Sunday evening with downstream surface=20
trough then low development off the Mid- Atlantic coast Sunday=20
morning. Strong right entrance dynamics aid fgen banding to=20
develop in the lee of the central Apps later this evening, most=20
likely over north-central MD east through NJ before the surface=20
trough/low offshore provides additional forcing for more intense=20
banding overnight and shifts the band south and east. This system=20
is fairly progressive, but the frontal forcing in increasingly cold
air allows 0.5-1.0"/hr rates in the Mid- Atlantic, extending to far=20
southern New England early Sunday. Marginal thermals at the=20
southern extend of the precip swath to begin with quickly shift to=20
all snow - this is aided by the nighttime occurrence. Snow ratios=20
could tip the scales to higher end amounts across parts of eastern=20
PA through Long Island and southern New England as omega intersects
with a wide DGZ as the precipitation shield pulls eastward,=20
supporting ratios closer to 15-20:1 and much higher than=20
climatology.

This event should last no more than 6-12 hours in any given=20
location, and the exact placement, timing, and intensity of the jet
streak and offshore trough is still somewhat uncertain. Today's=20
guidance trended a tick north and wetter due to a more amplified=20
upper trough and related right entrance region of a 150kt upper=20
jet. Day 1 PWPF for >6" are 30-50% from north-central MD through=20
southeast PA and central NJ. Probabilities for >6" are 20-40%=20
across Long Island and Cape Cod, including the islands off southern
New England. Given most of this snow is expected to occur=20
overnight and during a weekend, impacts may be limited, but strong=20
cold air advection following the event and very cold temperatures=20
could pose a danger for individuals caught unprepared outdoors. Be=20
sure to check conditions before traveling in this region tonight or
tomorrow morning.


...Great Lakes...=20
Days 1-3...

Aforementioned low pressure system stalling over Lake Superior
today ejects southeast tonight with a reinforcing shortwave trough
passage on Monday. Subterranean DGZ under the low today makes for=20
coarse/low SLR snow, but some warming this evening brings back the=20
dendrites and 20:1 SLRs to the U.P.

Day 1 PWPF for >6" are 40-80% over NWly flow snow belts in the=20
eastern U.P. and east of Grand Traverse Bay. Wly flow snow belts
east of Lakes Erie/Ontario result in Day 1 PWPF >6" of 30-50% east
of Cleveland to the Chautauqua Ridge and over 80% for the Tug Hill
where single banding LES sets up this evening. Lull expected
for Sunday night as low level ridging shifts east of the Lakes. But
then shortwave crosses Monday with a decent, but transient swath of
lake enhanced snow. Light to locally moderate synoptically driven
snow across the Great Lakes region Monday with more single banding
in westerly flow over Lake Ontario into the Tug Hill where Day 2.5
PWPF for >8" is over 80%.=20


...Pacific Northwest...
Days 2-3...

Potent atmospheric river arrives Monday morning to western WA/OR
with snow levels skyrocketing up to 9000ft over the Cascades. A
shortwave trough passage over WA late Monday brings snow levels on
the North Cascades down to 5000ft, reaching 4000ft on Tuesday.
Lower precip rates are expected behind the trough passage, but
moderate snow brings Days 2-3 PWPF for >8" in the 60-90% range in=20
the high northern WA Cascades. Additional snow is expected for=20
this region after the short range forecast period ends by 00z=20
Wednesday.


The probability of significant icing is less than 10 percent.=20

Snell/Jackson




...Extreme Cold Key Messages are in effect. Please see current Key
Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-y-EFOck4oiKPgryVMGcuJlO-9X4V4gIhgBlgpoo6TrGq= 8zrlWJ3ICxvhtyTseLzEz-LhdzxdCQUXLelwpLyVjJSkVU$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)