Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
511 PM EDT Mon Mar 22 2021

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

...Upper Midwest...
Day 2...
An upper trough/low currently moving east of the southern Rockies
is expected to lift northeast across northern Texas and Oklahoma
overnight.  While some wet snowflakes within the associated
deformation zone are expected, significant accumulations do not
appear likely.  This system is expected to produce mainly rain as
it tracks farther northeast from the central Plains on Tuesday and
into the upper Mississippi Valley Tuesday night.  Then as a
northern stream trough helps to bring colder air in behind the
system, the potential for accumulating snow is expected to
increase across northeastern Minnesota Wednesday morning, with at
least a few inches likely across portions of the Arrowhead.

...Great Basin and Southwest to the Central and Southern Rockies...
Days 1-3...
A well-defined shortwave currently dropping into the Pacific
Northwest will continue to dig south into California and the
central Great Basin overnight.  This is expected to support
widespread, but mainly light snow shifting southeast across the
Great Basin into the Rockies overnight.  As the shortwave
continues to dig south, models show a deep trough developing over
the Southwest late Tuesday into early Wednesday.  This will bring
snow farther south and east across Utah and northern Arizona and
through the Four Corners region on Tuesday.  Through late Tuesday,
expect accumulations to be mainly light, but with locally heavy
accumulations possible along the central southern Utah mountains
and along the northern Arizona high terrain.

By Tuesday evening, as a broad 700 mb low and area of increasing
ascent associated with the left-exit region of the upper jet
interact with an area of deepening moisture, the potential for
heavy snow is expected to increase from the eastern Mogollon Rim
and White Mountains of eastern Arizona into western New Mexico and
the San Juan Mountains.  Meanwhile, post-frontal, northeasterly
winds along with the supportive upper level dynamics will
encourage heavy snows developing farther east along the Sangre de
Cristo Mountains and the adjacent high plains of southeastern
Colorado and northeastern New Mexico Tuesday night into Wednesday.
 Snow is expected to continue into late Wednesday before
diminishing as the leading shortwave ejects northeast into the
central Plains.  Heaviest storm totals are expected along the
eastern slopes of the Sangre de Cristo and the adjacent mesas and
plains, with WPC PWPF showing high probabilities for snow
accumulations of a foot or more.


...Pacific Northwest through the Northern Rockies...
Days 1-3...
The upper trough digging though the western U.S. will draw a cold
front south through the northern Rockies.  Post-frontal,
low-to-mid level, northeasterly winds will promote snow showers
east of the Divide, with some locally heavy accumulations possible
along the Absaroka Range and Bighorn Mountains.  Another shortwave
trough diving south into the Pacific Northwest will bring mountain
snows back into the Cascades on Wednesday, and then portions of
the northern Rockies and the northern Intermountain Region
beginning late Wednesday and continuing into Thursday.

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

Pereira