602
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




$$