FOUS11 KWBC 030716
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
216 AM EST Sat Jan 3 2026

Valid 12Z Sat Jan 03 2026 - 12Z Tue Jan 06 2026

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

Impressive lake effect snow (LES) will continue today, especially
across the U.P. of MI and downwind of Lakes Erie and Ontario. This
LES has already been impressive, with 24-36 hour snowfall of 1-3
feet or more in some areas east of Lake Ontario, and today's LES
will likely be heavy once again. Continued CAA, reinforced at least
slightly by a weak shortwave moving overhead, will maintain steep
lapse rates and lake-induced instability to support snowfall rates
of 1-2"/hr as reflected by HREF 1"/hr snowfall probabilities
above 40%. A more NNW wind shift behind this shortwave will cause
bands to drop a little south of the recent heavy snowfall, and
WPC probabilities for an additional 4+ inches peak above 70%
southeast of Lake Ontario, with lower potential (10-50% chance)
across the eastern U.P. of MI and near the southtowns of Buffalo,
NY to the Chautauqua Ridge.

Thereafter, brief shortwave ridging envelops the region before a
more significant shortwave crests the western ridge and races
eastward towards the Great Lakes. This impulse will be of Pacific
origin, and accompanying elevated moisture (PWs above 0.5" and the
90th climatological percentile) will track in tandem with this
feature. Forcing for ascent driven by height falls/PVA,
intensifying left-exit jet level diffluence, and strengthening WAA
will provide the impetus for heavy snowfall, with 1"/hr snowfall
rates likely within any banded structures. The system will remain
progressive, and the guidance has trended a little SW over the past
few runs, but accompanying NBM probabilities have been relatively
steady. This indicates increasing confidence for a narrow swath of
heavy snowfall, for which WPC probabilities indicate a moderate
risk (50-70%) for 4+ inches across the U.P. of MI D2 into D3, with
several inches likely as well from near Duluth, MN through the
northern L.P. of MI.

Additionally, on the southern edge of this precipitation swath,
some mixed freezing rain/sleet is likely as the warm nose edges
northward in response to the pronounced WAA. This could result in a
corridor of impactful icing from far eastern ND through
central/southern MN and into southern WI. Although WPC
probabilities for 0.1" of ice are less than 10%, some icy roadways
and hazardous travel are possible Sunday evening.

...Western U.S. Mountain Ranges... Days 1-3...

A persistent mid-level trough positioned west of the Pacific Coast
will periodically shed impulses northeast and onshore, with each
subsequent impulse spreading energy across most of the
Intermountain West.

This persistent trough will manifest with 850-500mb heights that
will remain at or below the 10th climatological percentile into
Monday before finally relaxing. As spokes of vorticity swing out
from this trough and push onshore (the first likely this aftn with
a secondary impulse lifting northeast on Sunday night), the
subtropical origin will expand anomalous moisture onshore thanks to
surges of elevated IVT. As is typical with this setup, the
corresponding WAA will help drive snow levels upward, but a series
of cold front accompanying the aforementioned impulses will temper
the overall warming, leading to a general slow drop in snow levels
through the period. By Tuesday, as the core of the trough finally
pivots towards CA, snow levels could be quite low in the Cascades
and Pacific Northwest, only 1500-2500 ft, and just 3000-5000 ft
elsewhere after being as high as 6000-8000 ft to start the forecast
period. This suggests that each wave of precipitation through the
forecast period will result in more expansive and impactful snow at
lower elevations.

During D1, the heaviest snowfall is expected in the Sierra and
northern CA terrain where WPC probabilities for 12+ inches reach
70-90+ percent, and 1-3 feet is likely above 6000 ft. WPC
probabilities for 6+ inches D1 of more than 50% cover a large
portion of the Intermountain West terrain as well, with locally 1
foot possible in parts of the Wind Rivers, Sawtooth/Salmon River
ranges, and Cascades. During D2, waves of precipitation continue,
and support another day of heavy snow, focused across the Sierra
and Shasta/Trinity area, with lighter accumulations elsewhere, but
still covering much of the terrain from the Wasatch/Uintas and
points north and west. Multiple feet of snow is again expected in
the Sierra (WPC probabilities for 12+ inches above 90%) with more
than 1 foot possible in the higher terrain of the northern
UT/western WY, and into ID. Finally on D3, precipitation intensity
wanes, but additional significant snowfall accumulations are likely
in much of the area as this prolonged event begins to wane.

With extremely heavy snow likely in the Sierra and northern CA
mountains, totaling 4-6+ feet in some areas, and snow levels
falling below pass levels, travel will become extremely challenging
into early next week, and extreme impacts are possible due to the
combination of heavy snow and low SLR.


Weiss

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