Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
451 PM EDT Tue Mar 31 2020

Valid 00Z Wed Apr 01 2020 - 00Z Sat Apr 04 2020


...Pacific Northwest to the Upper Midwest...
Day 1 (ending 00Z Thursday)...
A series of shortwaves moving through the base of a broad upper
trough centered over the northwestern U.S. are expected to support
areas of impactful snow across portions of the region into the
latter half of the week.

Models show an initial system moving east from the Pacific
Northwest into the northern Rockies overnight, before lifting
north across the Dakotas on Wednesday.  Expect widespread light to
moderate snow accumulations from the Pacific Northwest to western
North Dakota, with embedded areas of heavier amounts.  These areas
include the higher elevations of central Montana - where upslope
flow on the north-side of a low level wave, along with favorable
upper jet forcing is expected to support higher totals across the
Big Snowy Mountains.  In addition to the Big Snowy Mountains, WPC
PWPF is showing high probabilities for accumulations of 8-inches
or more across portions of the western Montana and western Wyoming
ranges as well.

Day 2 (ending 00Z Friday)...
As the leading system lifts into central Canada, models show an
upstream wave moving across the northern Rockies into the High
Plains on Friday.  Favorable upper jet forcing will help to
support precipitation redeveloping north of a lingering boundary
setting south through the northern Rockies and Plains.  Upslope
flow is expected to bolster totals across potions of central to
eastern Wyoming and western South Dakota.  This includes the Black
Hills, Big Horns, Laramie and Shirley Mountains - where WPC PWPF
is indicating high probabilities for accumulations of 8-inches or
more.  Snow will extend northeast from central South Dakota to
eastern North Dakota, with generally lighter amounts expected
through Day 2.  Southeast of the developing snow band, a wintry
mix, with accumulating ice is expected across portions of the
eastern Dakotas, western Minnesota and northeastern Nebraska. 
With the 12Z models showing a fair amount of spread, forecast
confidence was less than average, especially across the northern
Plains and upper Midwest during this period.  WPC preference was
for the slower camp of solutions, which included the ECMWF and
UKMET.

Day 3 (ending 00Z Satuday)...
Shortwave trough over the High Plains Thursday evening will
continue to push east - driving additional snow and ice
accumulations across portions of the northern Plains and Upper
Midwest.  Additional accumulations over northeastern North Dakota
into northwestern Minnesota is expected to send storm totals over
4-inches across the region.  Meanwhile, light ice accumulations
will shift farther east to include Iowa and a larger portion of
Minnesota.     

Pereira