Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
338 AM EDT Fri Apr 29 2022

Valid 12Z Fri Apr 29 2022 - 12Z Mon May 02 2022

...Northern Rockies to Northern Great Plains...
Day 1...

Digging trough through Wyoming this morning will close off at
500mb by this evening as it moves into the Plains, in concert with
the surface system. Strong upper diffluence this morning will wane
as the best forcing moves out of the Rockies, but will still yield
several inches of snow over central Montana into Wyoming,
especially above 7000ft, as the 700mb low traverses through the
region. WPC probabilities for at least 4 inches of snow are
moderate (>40%) to high (>70%) over the Big Belt and Crazy
Mountains into the Bighorns.

As the low moves east of the Rockies, some rain changing to wet
snow is possible within the associated deformation zone over the
Dakotas; however, little to no accumulations are expected outside
of the Black Hills.  

...Northwest to Rockies...
Days 1-3...

Quasi-zonal flow out of the North Pacific will carry a new system
into the Pac NW this evening and into early Saturday with warm
advection snow into the Cascades. Upper low aloft will maintain
snow chances over the Cascades into Day 2 while spreading across
central Idaho. By Day 3, the system will weaken a bit but even its
limited moisture should support a few inches over Wyoming into
northern Utah and Colorado. WPC probabilities for at least 4
inches each day are low to moderate, focused over the highest
terrain.


For days 1-3, the probability of significant icing greater than
0.25 inches is less than 10 percent.


Fracasso