Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
416 AM EDT Thu Sep 27 2018

Valid 12Z Thu Sep 27 2018 - 12Z Sun Sep 30 2018


DAY 1...

...Northern Rockies/High Plains...
Models show shortwave energy embedded within northwest flow
sliding out of western Canada across the northern Rockies and High
Plains on Thursday.  Low to mid level frontogenesis along with
upslope flow is expected to support precipitation across the
region, with decreasing snow levels as colder air moves into the
region Thursday night.  Accumulating snows are expected along the
higher elevations of the northern Rockies from northwest Montana
to north-central Wyoming.  Heaviest amounts are expected to fall
along the Big Horns, with WPC Day 1 probabilities (ending 12 UTC
Fri) indicating a Slight Risk for accumulations of 8-inches or
more.  Accumulating snows are also possible further east across
the higher elevations of the Black Hills.

The probability of significant icing is less than 10 percent.

DAY 2...

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

DAY 3...

...Northern Rockies...
Mainly dry conditions are expected late Friday into early
Saturday, with precipitation returning to portions of the northern
Rockies around midday ahead of a shortwave trough digging through
western Canada.  Increasing upslope flow with low to mid level
frontogenesis, along with a reinforcing shot of cold air will
support another round of precipitation with decreasing snow levels
Saturday into early Sunday.  Heaviest snow accumulations are
expected to center along the higher elevations of the Lewis Range
in northwest Montana, with WPC Day 3 probabilities (ending 12 UTC
Sun) indicate a Moderate Risk for accumulations of 8-inches or
more.

The probability of significant icing is less than 10 percent.

Pereira