Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
411 PM EDT Thu Mar 25 2021

Valid 00Z Fri Mar 26 2021 - 00Z Mon Mar 29 2021


...Western U.S....
Day 1...
Areas of high elevation snow will once again spread south and east
from the Northwest and Great Basin into the Southwest and Rockies,
as energy diving south redevelops a deep trough over the
Southwest.  Heaviest amounts late Thursday into Friday are
expected to include areas of northern Arizona and the San Juan
Mountains in southwestern Colorado and far northern New Mexico,
where a period of enhanced, upslope southwesterly inflow ahead of
the amplifying trough is expected to promote heavier snowfall
rates Thursday night.  Latest WPC PWPF shows locally high
probabilities for snowfall accumulations of 8-inches or more
across those areas.

...Great Lakes to the Northeast...
Days 1-2...
Models continue to show the negatively-titled shortwave trough
currently lifting out of the southern Plains developing a compact
closed center as it tracks from the mid Mississippi Valley toward
the Great Lakes Thursday night.  A wintry mix, including some
snow, sleet and freezing rain, is expected across portions of
southern Wisconsin and Lower Michigan Thursday night and Friday
morning.
The latest WPC PWPF does show some low end probabilities for ice
accumulations of 0.10 inch or more across parts of southeastern
Wisconsin and northern Lower Michigan.  However, probabilities for
ice accumulations of 0.25-inch or more, and snow accumulations of
4-inches or more, are both less than 10 percent.  Then as the
system moves east from the Great Lakes into the Northeast, rain
changing to snow is expected across northern Maine as the system
moves offshore Friday evening.  This will likely result in at
least an inch or two of snow across northern Maine, with some
potential for accumulations of 4-inches or greater across northern
Aroostook County.

...Northern Minnesota...
Day 2...
A leading shortwave is expected to eject northeast out of the
western U.S. trough and lift northeast from the central Plains
into the Upper Midwest ahead of a northern stream trough moving
through the Dakotas on Saturday.  Models show precipitation
changing to snow along and behind the northern stream boundary as
it drifts across northern Minnesota on Saturday.  This will likely
produce at least an inch or two of snow across the Arrowhead, with
some threat for local amounts of 4-inches or more.

...Olympics and Northern Cascades...
Day 3...
Heavy snow is expected to return to the mountains with the
approach of a vigorous shortwave trough on Sunday, with
accumulations of 6-12 inches likely by Sunday evening across the
higher elevations of the Olympics and northern Cascades.

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

Pereira