Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
240 PM EST Tue Nov 12 2024

Valid 00Z Wed Nov 13 2024 - 00Z Sat Nov 16 2024

...Western U.S...
Days 1-3...

An amplified trough crossing the Rockies will continue to produce
high elevation snow showers across the northern and central Rockies
this evening. The greatest potential for significant additional
accumulations centers over the north-central Colorado ranges,
including southern portions of the Park Range, where WPC PWPF
indicates that amounts of 6 inches or more are likely during the
evening and overnight. Snow should diminish as the upper trough
shifts east on Wednesday.

Meanwhile, shortwave ridging over the Northwest will be replaced by
a broad upper trough associated with a low developing northwest of
Vancouver Island and energy digging to its south. Apart from the
northern Cascades, snow levels are expected to remain above 5000 ft
along much the Northwest ranges, limiting the potential for
widespread impacts through Wednesday. 

As the leading energy moves east through the northern Rockies
producing some isolated heavy amounts over the high terrain
Wednesday night into Thursday, upstream energy will continue to
amplify the flow along the West Coast, with a defined southern
stream low/trough developing and moving onshore Thursday night into
Friday. Lacking a long fetch of deep onshore flow, moisture with
this system will be limited. Therefore, while at least a few inches
of snow appears probable for areas in the Sierra above 5000 ft,
widespread heavy accumulations are unlikely.

The probability of significant ice across the CONUS is less than
10 percent.

Pereira