Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
413 AM EDT Wed Oct 03 2018

Valid 12Z Wed Oct 03 2018 - 12Z Sat Oct 06 2018

Day 1...
...Northern Plains...
A shortwave trough currently impacting the northern Rockies and
High Plains is forecast to move progressively east, with
precipitation waning across the northern Rockies Wednesday
morning.  Precipitation moving east across the northern High
Plains, will include mixed precipitation with some light snow
accumulations possible along the international border from 
northeastern Montana into northern North Dakota.  WPC Day 1
probabilities indicate a Slight Risk for accumulations of 4-inches
or more across this area. 
 
...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 2...

...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.  While not a widespread heavy snow threat, WPC Day
2 probabilities indicate the potential for localized amounts of
8-inches or more across some of the higher elevations.

...Northern Plains...
A remnant shortwave trough associated with the upper low moving
into California on Wednesday is expected to lift northeast out
ahead of the shortwave trough digging into the Northwest on
Thursday.  Models have been trending colder over the past few
runs, showing a greater signal for accumulating snows as the
system moves across North Dakota Thursday night, with WPC Day 2
probabilities (ending 12 UTC Fri) now indicating a Slight Risk or
more for accumulations of 4-inches or greater across a large
portion of central and eastern North Dakota.  Although the models
have been trending colder, the NAM is relatively cold outlier at
this point -- producing accumulations greater than the model
consensus across North Dakota into central and northern Minnesota.

The probability of significant icing is less than 10 percent.

Day 3...

...Northern and Central Rockies/Northern Plains...
The shortwave trough moving into the northern Rockies on Thursday
will continue to move east into the High Plains on Friday.  Low to
mid level frontogenesis and upslope flow may help produce some
high elevation snows from western and central Wyoming and northern
Utah to central Colorado on Friday.  Some additional snows are
also possible across northern North Dakota as the upper trough
moves across the state on Friday.

The probability of significant icing is less than 10 percent.

Pereira