Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
311 AM EST Sat Dec 21 2019

Valid 12Z Sat Dec 21 2019 - 12Z Tue Dec 24 2019


Days 1-3...

...Western U.S....

Ongoing heavy precipitation event over the Northwest will continue
to slide slowly south as the associated upper trough moves
gradually inland.  Additional heavy snows are possible on Saturday
across portions of the Cascades and far northern Rockies.  However
as a wave developing farther to the south helps to disrupt the
deeper moisture advection into the region, snows are expected to
diminish across these areas by late Saturday. 

By late Saturday and continuing into Sunday the heaviest snows are
expected to focus farther south near an amplifying wave moving
inland across northern California.  Heavy snows are expected to
develop across the Siskiyou and Shasta Cascade region late
Saturday into the overnight before extending farther east into the
Sierra on Sunday.  By late Sunday snows are expected to taper off
across much of northern California. 

A well-defined shortwave dropping south will amplify the upper
trough offshore before moving inland across Southern California
late Monday into early Tuesday.  This may support locally heavy
snowfall accumulations across portions of the southern Sierra and
the Transverse Ranges on Monday into early Tuesday.

The probability of significant icing (0.25-inch or greater) is
less than 10 percent.

Pereira