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
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
around freezing will drop into the 20s in wake of the front,
allowing for untreated surfaces to become icy and hazardous.
Whether it be by snow accumulating on all surfaces, melting and
refreezing on untreated surfaces, or the rapid reductions in
visibility, snow squalls have the potential to produce dangerous
driving conditions in the matter of seconds. *WPC continues to issue
Key Messages for the snow squall threat for today* (see Key
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... 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
today will weaken as it makes its way east. Despite this 500mb
trough losing its punch, a strong ridge of high pressure over the
Bahamas and a large upper-low over Hudson Bay has led to the
formation of a robust 250mb jet streak oriented SW-NE over the
east-central U.S.. Beneath the diffluent right-entrance region, a
weak wave of low-pressure along central Gulf Coast will escort a
plume of Gulf moisture northeastward into a frigid air-mass of
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, especially
for the Thursday PM rush hour and overnight Thursday.
As the upper trough approaches the Mid-Atlantic Thursday night,
enhanced 290K isentropic ascent and increasing 850-700mb WAA aloft
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 Thursday night and into 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
over-running 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 show moderate chances (40-60%) 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. 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
and Rockies through Friday and linger into Saturday. Synoptic-scale
forcing will be present throughout the Northern Rockies through
Friday, then over the Central Rockies late Friday into Saturday as
a stubborn 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
into 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.
Probabilities become even more impressive Day 2 and 3 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 2 and 3 reach above 70% for 8+ inches, and Day 2
and Day 3 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". 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... 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
storm as it reaches the Central Plains on Saturday. 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, but exactly
where this band sets up is low confidence.
At the moment, WPC probabilities show minor snowfall totals (1-3")
generally having moderate-to-high chances (30-50%) across the
northern High Plains through Saturday morning. The high degree of
spread in model solutions is causing WPC probabilities to sport low
chances (10-30%) for snowfall totals >4" from southeast SD and
northeast NE on east through southern MN and northern IA. That
being said, the favorable synoptic and mesoscale processes at play
could very much support a band of >6" snowfall totals that causes
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
shows 40-60% chances for Minor Impacts from southeast SD and
northeast NE on east through southern MN and northern IA) but
details as to which areas are likely to see the worst impacts are
still unclear at this time.
Mullinax
...Winter Storm Key Messages are in effect. Please see current
Key Messages below...
https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png
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