Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 PM EDT Mon Oct 01 2018

Valid 00Z Tue Oct 02 2018 - 00Z Fri Oct 05 2018


Days 1/2...

...Northern Rockies...
Models continue to show a well-defined shortwave trough digging
south through British Columbia on Tuesday before pivoting
southeast across the Pacific Northwest into the northern Rockies
late Tuesday into early Wednesday.  North of the low track, strong
low level frontogenesis and cooling temperatures will bring the
threat for heavy snow south along the Rocky Mountain front/Glacier
National Park in northwest Montana Tuesday to Wednesday, with
models continuing to signal the potential for heavy accumulations
around a foot in higher elevations.  The higher probabilities are
focused on Tuesday and subside eon Wednesday. The models cluster
well so no solution was given more weighting than other model
runs. 

The probability of significant icing is less than 10 percent.

Day 3...

...Sierra...
An upper low dropping south along the California coast on Tuesday
and Wednesday is expected to move inland Wednesday night, with the
arrival of the low resulting in enhanced moisture and lift
crossing the ranges of CA.  High elevation snow is expected across
the Sierra Nevada range.  The event concludes Thu as the 700 mb
trough moves further inland, followed by weakening lift and drier
air aloft resulting in reduced coverage/intensity of snow showers.
WPC probabilities show some chance for accumulations of 4 inches
or more, mainly for elevations above 9500 ft.

The probability of significant icing is less than 10 percent Days
1-3.

Petersen