Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
410 PM EDT Sun Oct 30 2022

Valid 00Z Mon Oct 31 2022 - 00Z Thu Nov 03 2022

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

An atmospheric river being directed into Washington today will
drift south tonight into Monday as a low over the Gulf of Alaska
ejects southeast. The associated trough and a reinforcing
shortwave trough will push across the Pacific Northwest Tuesday
before digging farther south to the Desert Southwest through the
midweek. High snow levels inherently accompany the atmospheric
river with 7000-9000ft snow levels through the axis of moisture.
Day 1 snow probabilities for over 4 inches are limited to the
highest WA Cascades as well as low probabilities on the Lewis
Range in Glacier NP.

As the river shifts south and troughing increases, the moisture
stream is cutoff a bit and snow levels to the north drop to around
2500ft with continued onshore flow. Moderate to locally heavy snow
shifts south down the rest of the Cascades through the central
Sierra Nevada and shifts east to the northern Rockies. Snow
probabilities for 12Z Tuesday to 12Z Wednesday are moderate to
high for 6 or more inches for northwestern MT ranges,
north-central and northeastern OR ranges, the southern OR and CA
Cascades as well as the northern and central Sierra Nevada where
snow levels will generally be 5000-6000ft.


The probability of significant icing greater than 0.25" is less
than 10 percent.

Jackson