Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
412 PM EDT Sat May 7 2022

Valid 00Z Sun May 8 2022 - 00Z Wed May 11 2022

...Cascades and Sierra to the Northern Rockies...

Days 1-3...
The overall synoptic scale pattern will be featured with a
building upper level trough over the northwestern quadrant of the
U.S. through early next week, with the magnitude of the 500 mb
height negative anomalies increasing on Sunday as a potent trough
and potential closed low crosses Oregon, and then result in height
falls for the Northern Rockies Sunday night into Monday morning. 
There will likely be a second anomalous upper low in the general
vicinity of northern California for early Tuesday that will tend
to remain quasi-stationary as an omega block pattern develops over
the central U.S.  Both of these features will have 850 mb
temperature anomalies on the order of 10C (18F) below early May
climatology, leading to lower snow levels with accumulating snow
likely at pass levels. 

In terms of the snow forecast, the greatest accumulations are
likely to be realized during the day one period through Sunday
evening across the higher terrain of northwestern California and
the Oregon Cascades, where the best potential exists for 6-12 inch
totals as the first shortwave moves through.  There is a low end
probability of some 12+ inch totals for the highest ridges.  There
will likely be enough forcing across the Absaroka Mountains for
similar totals here as well.  For the day three period on Tuesday,
light to perhaps moderate snow becomes increasingly likely for
much of the central and northern Sierra as the California system
moves in.

For days 1-3, the probability of significant icing is less than 10
percent nationwide.

Hamrick