Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
411 AM EDT Tue Oct 02 2018

Valid 12Z Tue Oct 02 2018 - 12Z Fri Oct 05 2018


Day 1...

...Northern Rockies...
As a well-defined shortwave trough digging south through British
Columbia pivots east across the Pacific Northwest and northern
Rockies, there remains a good model signal for heavy snows
extending south from the Canadian into the far northern U.S.
Rockies Tuesday into early Wednesday.   Supported by low level
northerly-northeasterly winds, heaviest amounts are expected to
fall across the higher elevations of northern Glacier National
Park, where WPC probabilities continue to indicate a moderate risk
for accumulations of a foot or more by 12 UTC Wednesday. 

The probability of significant icing is less than 10 percent.

Day 2...

...Northern Plains...
The previously noted shortwave is forecast to move progressively
east, with precipitation waning across the northern Rockies after
12 UTC Wednesday.  Precipitation moving east across the northern
High Plains, will include mixed precipitation with some light snow
accumulations possible along the U.S./Canada border from
northeastern Montana into northwestern North Dakota.

...Sierra...
An upper low dropping south along the California coast on
Wednesday is forecast to move inland overnight, producing some
high elevation snows over the Sierra.  WPC probabilities continue
to indicate the potential for accumulating snows for elevations
above 9000 ft.

The probability of significant icing is less than 10 percent.

DAY 3...

...Northern Rockies...
Models show a shortwave trough digging southeast across the
Pacific Northwest into the northern Rockies late Thursday into
early Friday.  This is forecast to result in mountain snows from
western Montana and central Idaho to perhaps as far south as
northern Utah.  Greater threat for heavier amounts is across the
southwestern Montana and northwestern Wyoming ranges, with WPC
probabilities indicating a Slight Risk for localized amounts of
8-inches or more.

The probability of significant icing is less than 10 percent.

Pereira