Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
333 AM EST Sun Mar 07 2021

Valid 12Z Sun Mar 07 2021 - 12Z Wed Mar 10 2021


...Pacific Northwest/California to the Northern Rockies...
Day 1-3...

Three shortwave troughs round a low pressure system shifting south
from off the BC coast and down the West Coast, tracking into The
West through midweek.

The first wave is reaching the WA/OR coast early this morning and
will lift northeast over WA today. 0.5" PW air pushing to the WA
Cascades will make for moderate mountain snow today with moderate
Day 1 snow probabilities for 6 or more inches for the Olympics and
high WA Cascades with snow levels dropping to around 1500ft this
morning.

The second shortwave trough is currently just reaching the low
pressure system from the central Gulf of Alaska, it amplifies the
surrounding trough through tonight before swinging east-northeast
across northern CA Monday, the northern Great Basin to MT Monday
night. Left-exit region upper jet forcing along with a low-to-mid
level baroclinic zone dropping southeast is expected to interact
with a modest increase in moisture to support increasing
precipitation coverage from Northern California to western
Montana. Day 2 snow probabilities for 6 or more inches are
moderate in the Klamath and CA Cascades, the Wallowa Mtns of
northeast OR, the Salmon River and Clearwater Mtns of ID as well
as ranges in central MT.

The third shortwave trough ejects south from the eastern Gulf of
Alaska tonight, amplifying the trough even further south before
ejecting east-northeast across the central CA coast Tuesday,
crossing UT Tuesday night. High level Pacific moisture wraps
around the lee-side surface cyclone that develops over the central
High Plains Tuesday night, aiding a swath of higher elevation snow
(snow levels around 5000ft) to develop across WY to the Black
Hills that continues through Wednesday. Day 3 snow probabilities
for 6 or more inches are moderately high for the Klamath Mtns,
down the full extent of the Sierra Nevada and low for ranges in
east-central NV, the northern Wasatch in UT, and around the
Bighorn Mtns in WY.


For Days 1-3, the probability of significant icing (0.25-inch or
greater) is less than 10 percent.

Jackson