FOUS11 KWBC 020914
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
414 AM EST Sun Feb 2 2025

Valid 12Z Sun Feb 02 2025 - 12Z Wed Feb 05 2025


...Western U.S. across the Northern Plains...
Days 1-3...

...Atmospheric River (AR) and upper low maintain prolonged heavy
snow from Oregon/California border to the Northern Rockies through Monday...

Deep upper low persists over Vancouver Island through Monday before
drifting southwest off the PacNW coast with troughing lingering
there through Thursday. Another upper low moving east to the north
of Hawaii moving eastward will maintain onshore flow into the West
over the next several days, focusing the moisture axis from CA/OR
border through southern Idaho through western WY terrain through
Monday before shifting south over CA Monday night through Tuesday
night. Tight baroclinic zone north of this moisture axis maintains
lower elevation snow with enhanced totals in terrain through this time.

48hr probs for >2' ending 12Z Tuesday are 50-90% over terrain from
the Shasta/Siskiyou. Fremont Mtns in southern OR, the Sawtooths,
and Yellowstone through Wind Rivers. Beneficial precip for this
area, but major impacts to any passes in this area with snow levels
around 4000ft in the heavier snow. Snow levels are 5000-8000ft in
the core of the AR moisture axis over northern CA/NV/UT. However,
on Monday afternoon height falls as troughing expands over the NW
low brings snow farther south into CA. Heavy snow reaches the
northern Sierra Nevada by Monday evening with a slow progression of
heavy snow down the length of the Sierra with hourly rates
exceeding 2"/hr into Wednesday. Day 3 probs for >1' are 60-95% for
the length of the Sierra Nevada with a few feet in the High Sierra
(snow levels generally 5000-6000ft in the heaviest snow.

Cold continues over western WA/OR with occasional snow in the
Seattle/Portland metro areas through Tuesday night. A few to
several inches at a time are possible given the banding potential
under/adjacent to the upper low just to the north.

The tilting axis that brings snow to CA Monday night also shifts
snow across the northern Rockies through MT through Tuesday night.
Day 3 snow probs for >4" are high over the Sawtooths and Absarokas
(adding to the extreme totals of the previous two days) with 40-60%
probs over the Bitterroots and all western MT ranges into the
north-central MT Plains.


...Northern Plains, Great Lakes, Northeast...
Days 1-3...

Zonal flow sends two shortwave troughs east over the northern tier
through Monday night.

Shortwave trough axis over MN shifts east across the Great Lakes
and New England through tonight. Final snow band works over the
North Shore in MN through mid-morning with locally heavy rates from
southeasterly flow lifting over the Arrowhead. Expanding precip
shield over MI rest of the morning where a couple inches are
possible with more moderate snow across the Northeast late
afternoon through the evening. Local terrain enhancements over the
Tug Hill/southern Adirondacks/Berkshires/Greens/Whites and coastal
Maine where Day 1 snow probs for >4" are 20-40%.

The next shortwave trough enters the northern Plains this afternoon
with east-west oriented snow bands forming in the left exit region
of a 130kt+ jet streak producing a narrow axis of moderate snow
from southeast MT and along the SD/ND border where Day 1 snow probs
for >4" are 30 to 60%. These bands maintain their strength as they
shift east across central MN/northern WI and the northern L.P. late
tonight through Monday morning where Day 1.5 snow probs for >4" are 30-60%.

This jet induced swath of snow shifts across Ontario Monday, then
grazes northern NY and northern New England Monday night. Day 2
snow probs for >4" are 40-80% for the northern Adirondacks,
northern VT/NH, and northern Maine.


Jackson

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