Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
420 AM EST Fri Mar 12 2021

Valid 12Z Fri Mar 12 2021 - 12Z Mon Mar 15 2021


...California to the Central Rockies and High Plains...
Days 1-3...

The overnight models continued to show a strong signal for a major
storm system that will likely bring heavy snows to portions of the
central Rockies and High Plains beginning Friday and continuing
through Sunday.  This will include the I-25 urban corridor from
Cheyenne to Colorado Springs.

The upper level feature associated with this storm -- a deep upper
trough/closed low -- is currently over California.  As the upper
low slowly turns east, expect the ongoing, generally scattered and
light-to-moderate, high elevation snows to continue from Southern
California into the Great Basin, Southwest and central Rockies
through Friday into early Saturday.  While widespread heavy totals
are not expected, some areas could see locally heavy amounts. 
This includes portions of the Mogollon Rim in central Arizona and
the southern Utah mountains.  A period of deep southerly flow
ahead of the approaching low along with favorable upper forcing
may help bolster amounts.  For the Day 1 period (ending 12Z
Saturday), WPC PWPF shows locally high probabilities for
accumulations of 6-inches or more across those areas.

By early Saturday, strengthening southerly, low-level winds will
begin to transport deeper moisture up through Texas into the
central High Plains, where a developing wave will begin to direct
that moisture back into the high terrain.  As the low moves
farther east, increasing moisture and large-scale ascent will
support widespread heavy snows developing across the central
Rockies and High Plains on Saturday, continuing into Sunday.  For
the Day 2 period (ending 12Z Sunday), WPC PWPF shows widespread
probabilities of 50 percent or greater for snow
accumulations of 8-inches or more covering much of southeastern
Wyoming and central Colorado. This includes the urban I-25
corridor from Cheyenne to Colorado Springs.  WPC PWPF shows that
heavier totals on the order of 18-inches or more are likely just
east of the corridor into the Front Range and the Laramie
Mountains.  Farther to the east, probabilities for significant
accumulations have come down some over the western Nebraska
Panhandle -- a reflection of a general warming trend several of
the overnight models showed across the High Plains.

As the low moves across the central Rockies into the High Plains,
heavy snows are likely to continue through the day on Sunday
across portions of central Colorado and southeastern Wyoming.  WPC
PWPF indicates that additional accumulations of 6 to 12 inches are
likely along the I-25 Corridor from Denver through Cheyenne, with
heavier amounts likely farther west across the mountains.  Through
early Monday, storm total amounts of 2 feet or more are likely
along the Laramie Mountains and the Front Range. 

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

Pereira