Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
426 AM EDT Sun May 08 2022

Valid 12Z Sun May 08 2022 - 12Z Wed May 11 2022

...Coastal to Sierra and Cascade Ranges in Northern California and
Western Oregon to the Northern Rockies...

Days 1-3...
The overall synoptic scale pattern will be featured with an
amplifying upper-level trough over the northwestern quadrant of
the U.S. into the middle of next week, with the magnitude of the
500 mb height negative anomalies peaking between 2.5 to 3 standard
deviations below normal Sunday into Monday across Oregon and
northern CA eastward into the northern Intermountain West and
northern Rockies. Given the mid-upper level blocking and trough
re-loading across the central-northern west coast, 850 mb
temperature temperatures will average around 10C (18F) below early
May climatology, or around 2 standard deviations below normal,
leading to lower snow levels (~2500 ft) 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 12Z
Monday) across the higher terrain of northwestern California and
the Oregon Cascades, where the best potential exists for 6-12+
inch totals across the far eastern coastal ranges into the Klamath
Mountains, Shasta/Siskiyous, and southern Cascades of northern CA
into western OR as the first upper jet streak and associated
shortwave trough move through. There is a low end probability
(25-40%) 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.

Hurley/Hamrick