Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
434 AM EST Sun Dec 22 2019

Valid 12Z Sun Dec 22 2019 - 12Z Wed Dec 25 2019


Days 1-3...

...Western U.S....

A series of shortwaves moving through the base of a longwave
trough will produce periods of organized snow and possibly
localized heavy accumulations from  the mountains of California to
the central Rockies this period.

A slow-moving frontal boundary that has been lingering along the
coast of Northern California is expected to push farther inland as
a shortwave moving through the base of the trough lifts northeast
across Northern California and Oregon on Sunday.  As snow levels
fall, this will support significant snowfall accumulations from
the Klamath Mountains in northwestern California into the Shasta
Cascade region and then along the Sierra on Sunday.  As this
system lifts out to the northeast, expect snows to diminish across
much of Northern California by Sunday evening.

Meanwhile, an upstream wave will begin to approach the Southern
California coast as it lifts ahead of mid level low dropping south
from the Gulf of Alaska.  This will bring organized precipitation
into Southern California on Monday, including some possibly heavy
snowfall accumulations for the southern Sierra and Transverse
Ranges.

This system is forecast to swing east into the southwestern U.S.
on Tuesday -- producing some moderate to locally heavy snows along
the Mogollon Rim and White Mountains in central to eastern
Arizona, as well as the San Juan Mountains in Colorado.

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

Pereira