Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
358 AM EST Mon Dec 23 2019

Valid 12Z Mon Dec 23 2019 - 12Z Thu Dec 26 2019


Days 1-3...

...California to the Rockies....
A broad scale trough centered over the western U.S., with several
embedded shortwave features, will continue to produce unsettled
weather, including periods of moderate to heavy snow from
California to the Rockies.

Shortwave energy currently moving through the base of the trough
is expected to lift northeast across Southern California as a
second system digs south.  This will likely produce several inches
of snow across the higher elevations of the Transverse Ranges in
Southern California, as well as across portions of the southern
Sierra on Monday.  This initial system is then expected to produce
generally light amounts across the Great Basin as it lifts
northeast of the Sierra Monday night into Tuesday.

By early Tuesday, models show the upstream wave approaching
northern Baja California before swinging inland across
northwestern Mexico and the southwestern U.S. later in the day. 
This system is expected to bring high elevation snows, with
potentially locally heavy accumulations, to central and northern
Arizona on Tuesday and the western Colorado ranges Tuesday night
into early Wednesday.

On Wednesday, models show yet another system digging quickly south
along the California coast.  This is expected to bring at least
additional light accumulations to the California mountains. 
Shortwave energy embedded within diffluent flow ahead of the low
will also support additional light, high elevation snows across
the Southwest into the central Rockies Wednesday into early
Thursday.

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

Pereira