Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
437 AM EDT Sat Oct 24 2020

Valid 12Z Sat Oct 24 2020 - 12Z Tue Oct 27 2020


...Western and Central U.S. Winter Storm...

As an upper trough continues to amplify over the western U.S., a
significant winter storm will continue to move south along the
Rockies and extend east into the northern and central Plains over
the weekend. 

As snows continue across the northern Rockies, a mid level low and
favorable upper jet forcing associated with an amplifying trough
over the northwestern U.S., will carry snows eastward into the
portions of the northern Plains on Saturday.  Supported in part by
right-entrance region upper jet dynamics, several inches are
possible across portions of southeastern North Dakota and western
to central South Dakota.  Meanwhile to the west, favorable upper
forcing along with strong low-to-mid level frontogenesis will
contribute to heavy snows moving south through the northern
Rockies on Saturday, with accumulations of a foot or more likely
for portions of the western Wyoming ranges.

As the upper trough continues to amplify and settle south across
the western U.S., the threat for heavy snow is forecast to shift
into the central Rockies and High Plains on Sunday.  Heavy
accumulations are likely across portions of the Colorado Rockies,
with WPC PWPF indicating high probabilities for accumulations of a
foot or more for the north-central Colorado ranges.  Impactful
accumulations are also expected from the Front Range eastward into
the I-25 corridor, with WPC PWPF showing probabilities of 50
percent or higher for accumulations of 6-inches or more for this
area, including the Denver metro.  While generally lighter amounts
are expected farther east, there is the potential for locally
heavy accumulations well out into the Plains, with WPC PWPF
showing high probabilities for accumulations of 4-inches or more
extending into central Nebraska.

By early Monday, expect the greater potential for heavy snow to
shift south into the southern Colorado and northern New Mexico
ranges.  As an upper low begins to close off over the Southwest,
accumulating snows will become likely along the Mogollon Rim in
central Arizona.

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

Pereira