Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
404 PM EST Mon Feb 22 2021

Valid 00Z Tue Feb 23 2021 - 00Z Fri Feb 26 2021


...Northern Plains to the Northeast...
Days 1-3...
A well-defined shortwave dropping southeast into the Pacific
Northwest Monday evening is forecast to move quickly east --
reaching the northern High Plains by mid Tuesday.  Models have
been trended upward with QPF/snow amounts associated with this
progressive, but dynamic system as it moves across the northern
Plains, Upper Midwest and Great Lakes on Tuesday and Wednesday. 
In addition to favorable upper forcing, strong low-mid-level
frontogenesis will likely be supportive of a period of moderate to
heavy snow shifting east across North Dakota into northern
Minnesota on Tuesday, and then across northern Minnesota into
northern Wisconsin and northern Michigan Tuesday night into
Wednesday morning.  Latest WPC PWPF shows a narrow stripe of 2-4
inches, with locally heavier amounts, likely across this region. 
As the system moves to the east late Wednesday, there is some
indication that northwesterly flow on the backside of the system
may contribute to some lake-enhanced totals across portions of the
eastern U.P. and northern Lower Michigan.  This system is expected
to move across southern Ontario and Quebec Wednesday evening,
before brushing northern New York and New England with some light
amounts Wednesday night into early Thursday.

...Pacific Northwest to the Northern Rockies...
Days 1-3...
A trio of systems is expected to bring periods of heavy mountain
snow as they move across the region over the next few days.  The
first system, (noted previously), is forecast to produce heavy
snows as it moves across the region Monday night.  Areas impacted
are expected to include the northern Cascades, the Blue Mountains
and the Rockies from northern Idaho and western Montana to western
and central Wyoming.  This system will be quickly followed by a
second shortwave dropping southeast into the Northwest on Tuesday
-- bringing additional heavy snows to portions of the region late
Tuesday into early Wednesday.  Shortwave ridging behind this
system will provide short period of dry weather before the third
system drops into the Northeast on Thursday, with heavy snows
likely across the Olympics and northern Cascades.

...Central Rockies/High Plains...
Day 3...
Snows are expected to develop across the central Rockies as the
shortwave trough digging across the Northwest on Wednesday
continues to dig southeast and approaches the region Wednesday
evening into the overnight.  Low-level, convergent, upslope flow
is expected to support snow developing over the Colorado High
Plains and foothills Wednesday night into early Thursday, with WPC
PWPF showing 50 percent or greater probabilities for accumulations
of 4-inches or more along a good portions of the I-25 corridor.


For Days 1-3, the probability of significant icing (0.25-inch or
more) is less than 10 percent.

Pereira