621
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...
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
move east across the Midwest on Tuesday, reaching the East Coast
late in the day, before becoming negatively-tilted as it moves off
of the Mid Atlantic/Northeast coasts Tuesday night.

At the surface, low pressure will develop over the northern Gulf
tonight before energy transfers to low pressure along the
Southeast coast. Supported by a coupled upper jet, this low will
deepen quickly as it tracks north along the Mid Atlantic to the
Northeast coast on Tuesday. With the 12Z ECMWF now shifted north,
the general consensus of the deterministic runs and the ensemble
means show the low tracking near the 40N/70W benchmark around 00Z
Wednesday before continuing on a track east of the Canadian
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
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
the larger system developing near the Gulf as impressive moist
isentropic ascent supports a north-moving theta-e ridge and an
expanding precipitation shield. Strong 850mb WAA will provide
additional ascent, with the accompanying frontogenesis serving to
intensify omega into the DGZ. While the WAA will likely result in a
burst of moderate snowfall in many areas across the interior Mid
Atlantic into the Northeast, a lack of resupplying cold air as a
surface high to the north retreats will enable a quick transition
to mixed/rain, especially along and east of the I-95 corridor from
northern Virginia to Boston. The 12Z models trended slightly
warmer, further indicating that areas from DC to NYC will be
mostly, if not entirely, all rain. However, northwest of the I-95
corridor, the story remains much different, where a prolonged
period of moderate, to at times heavy snow, is likely, with 1+"/hr
rates spreading from Pennsylvania to Maine. This will create an
axis of snowfall for which WPC probabilities continue to show a
high risk (>70% chance) for 4+ inches from the Poconos through
Downeast Maine, with locally as much as 8-12 inches possible (50%
chance) across parts of the Catskills and from the Berkshires to
southern Maine, including the northern Worcester Hills and
Monadnock region.

South of the heavy snow axes, light ice accumulations will shift
northeast from southern Arkansas into eastern Tennessee and
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
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
western Maryland. Although the high to the north will be
retreating, this cold air may be more difficult to scour out,
especially in the more sheltered locations, leading to an extended
period of freezing rain with impactful ice accretions likely. WPC
probabilities show 50 percent or greater probabilities for at least
0.1 inch of ice from across parts of western North Carolina
northward along the southern Blue Ridge into southern West Virginia
and the Shenandoah region of Virginia, with a low chance (10-30%)
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...
Days 1-3...

A shortwave will dig south out of British Columbia into the
northwestern U.S. overnight. This shortwave will continue to move
southeast Tuesday into Wednesday, and may become more amplified as
it drops through the Great Basin 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.

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
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
centered. The southern shift is expected to continue into Day 3,
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
along this front as it dives southeast. The trends in the GFS SnSq
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
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.

Pereira/Weiss

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

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_3.png


$$