Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
404 AM EDT Fri Sep 28 2018

Valid 12Z Fri Sep 28 2018 - 12Z Mon Oct 01 2018


Day 1...

The probability of significant icing and/or snow is less than 10
percent.

Days 2/3...

...Northern Rockies and High Plains...
Greatest potential for significant snow accumulations is expected
to occur Saturday into early Sunday and focus mainly across the
mountains of northwest Montana.  Precipitation is forecast to
redevelop across the region as a northern stream shortwave trough
moves across western Canada, while a weakening Pacific low
approaches from the west.  Low to mid level frontogenesis and
easterly flow will raise the potential for precipitation east of
the Divide while a reinforcing shot of colder air brings snow
levels down late Saturday into early Sun.  WPC probabilities
continue to signal the potential for significant accumulations
along the Lewis Range, showing a Slight Risk for accumulations of
8-inches or more during the Day 2 period (ending 12 UTC Sun). 
Precipitation is expected to continue into the Day 3 period and
spread east producing some light snow accumulations out into the
High Plains, with additional accumulations across the mountains as
well.  However, snow levels are expected to rise ahead of the
approaching Pacific wave, limiting the threat for any additional
significant amounts.  Then by early Monday, precipitation is
expected to wane as the Pacific system moves east. 

The probability of significant icing is less than 10 percent.

Pereira