Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
425 PM EDT Wed Mar 27 2019

Valid 00Z Thu Mar 28 2019 - 00Z Sun Mar 31 2019


...Northern Rockies to the Central Plains...

Shortwave energy and an associated plume of deeper moisture moving
out ahead of a weakening upper low anchored off of the Pacific
Northwest coast is expected to help support locally heavy mountain
snows across portions of the northern Rockies as it moves inland
Wednesday night.  Divergent flow aloft coupled with enhanced low
level convergence near a developing low level wave will help
generate some locally heavy accumulations centered across the
southwestern Montana ranges - where WPC probabilities show some
small Moderate Risk areas for accumulations of 8-inches or more on
Day 1 (ending 00Z Friday). 

As it begins to interact with an amplifying northern stream trough
over central Canada, models show the low level wave dropping
southeast from western Montana into Wyoming Thursday night.  This
may produce some locally heavy accumulations near the track of the
wave and along a trailing baroclinic zone extending back through
northern Utah.  As the leading energy moves east of the Rockies,
precipitation will develop across eastern Wyoming, western South
Dakota and Nebraska.  The amplifying northern stream trough will
support colder air moving south, with rain changing to snow
pushing south across the region on Friday.  This may result in
significant accumulations extending east from eastern Wyoming into
southwestern South Dakota and the Nebraska Panhandle, with WPC Day
2 probabilities (ending 00Z Saturday) indicating a Moderate Risk
for accumulations of 4-inches or more. 

Although WPC probabilities indicate the chance for significant
snows spreading farther east on Day 3, this is tied largely to the
NAM -- which with its 12Z run remained an outlier, showing a more
amplified southern stream wave with heavier snows spreading east
across the central Plains and Mississippi valley.

Pereira