Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
422 PM EDT Sat Apr 03 2021

Valid 00Z Sun Apr 04 2021 - 00Z Wed Apr 07 2021


...Northern Rockies...
Days 1-3...
A low-amplitude ridge is expected to give way to a
positively-tilted upper trough dropping south across western
Canada and the Pacific Northwest on Sunday.  Models show a split
in the upper pattern developing -- with a progressive northern
stream trough moving into central Canada on Monday, while in the
southern stream a closed low develops over the Pacific Northwest
before dropping southeast and tracking near the southern Idaho
border Monday night, to the southern Wyoming border on Tuesday. 
Compared with the overnight runs, the 12Z guidance showed better
agreement -- with the GFS now notably faster than its previous
runs.  This is expected to be a rather cold system, bringing snow
into the lower elevations of Idaho, western Wyoming and western
Montana.  While precipitation is expected to be widespread,
amounts are expected to be generally light to moderate across the
region.  This is reflected in the WPC PWPF.  While it shows
widespread high probabilities for three-day total snow
accumulations of 4-inches or more across the central Idaho,
western and central Montana, and western Wyoming ranges, it also
little potential for accumulations exceeding 8-inches across the
region.

For Days 1-3, the probability of significant icing (0.25-inch or
greater) is less than 10 percent.

Pereira