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FOUS11 KWBC 110849
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
449 AM EDT Tue Mar 11 2025

Valid 12Z Tue Mar 11 2025 - 12Z Fri Mar 14 2025


...The West...
Days 1-3...

...Impactful heavy snow for most California mountain ranges
Wednesday into Thursday, then mostly the southern Intermountain
West and Rockies late week. Please see current Key Messages linked
below...

A strong northern stream trough currently rounding a cold-core low
over the Gulf of Alaska will further strengthen as it dives south
off the West Coast through Wednesday. The base of the trough
continues to dig south from the Central to Southern California
Coasts Thursday before ejecting east over the Four Corners Thursday
night and re-developing into a deep low over the south-central
Plains Friday.

Mountain snow begins tonight as moisture streams in ahead of the
trough axis along the length of the Cascade Range through the
Siskiyou/Shasta and northern Sierra Nevada. Day 1 snow
probabilities for >6" are 30-70% in the WA Cascades which will
expand and increase for Day 2 as snow rates increase to moderate
and snow levels drop below many Cascades passes.

This moisture surge shifts inland over CA Wednesday through
Wednesday night with the now heavy precipitation axis shifting
south with the base of the trough with snow levels generally 5000
to 6000ft at the onset of heavy snow. Height falls from the
approaching trough axis allow snow levels to drop Wednesday
afternoon through night along the Sierra Nevada with heavy snow as
low as 4,500ft in elevation before rates decrease (as low levels
further drop). The cooling column and ample moisture should result
in extreme hourly snowfall rates of 2-4"/hr in these ranges. The
combination of heavy/wet snow and increasing winds also posing a
potential risk for scattered areas of power outages and tree
damage. Day 2 snow probabilities for >18" are 50-99% in the
Shasta/Siskiyou and along the length of the higher Sierra Nevada.
1 to 4ft can generally be expected above about 6000ft.

Heavy snow will also reach the Transverse Ranges in Southern
California Wednesday night through Thursday morning with snow
levels dropping from around 6000 to 4000ft. Day 2.5 WPC snow
probabilities are 50-90% for the higher San Gabriel and San
Bernardino Ranges. 00Z Wed

East of the Pacific Mountain ranges, the expansive swath of
Pacific moisture will expand well inland Wednesday night through
Thursday night. The heaviest inland snowfall is likely to occur on
Thursday as the powerful cold front sweeps across Nevada, Utah, and
northern Arizona before shifting across Colorado and New Mexico
Thursday night. Day 3 snow probabilities for >8" are 40-80% over
the central and southern NV ranges, much of Utah terrain, the
Kaibab Plateau north of the Grand Canyon, along the Mogollon Rim to
the White Mtns of AZ, and the San Juans of southwest CO. This low
rapidly re-develops Friday over the south-central Plains.

The next wave quickly shifts toward the OR/CA border Thursday night
on a powerful NWly jet. Further info on the redeveloping low over
the Plains and the next wave into the West Coast can be found in
the WPC medium range discussion (PMDEPD), and from local WFOs.


The probability of significant icing is less than 10 percent.

Jackson


...Winter Storm Key Messages are in effect and linked below...

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png

$$