Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
405 AM EST Thu Mar 11 2021

Valid 12Z Thu Mar 11 2021 - 12Z Sun Mar 14 2021


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

Confidence continues to increase that a major winter storm will
bring heavy snow to portions of the central Rockies and High
Plains beginning on Friday and continuing through early Sunday. 
This includes the I-25 corridor from Cheyenne through Denver. 

This storm is associated with a deep upper trough/low currently
centered over California.  This system is expected to drop farther
southeast over the coming day, supporting widespread light to
moderate, high elevation snow from central and southern California
to the central Rockies.  Areas impacted are expected to include
the Southern California coastal ranges, southern Sierra, the
southern and central Nevada mountains, the Arizona Rim Country,
and the southern and central Utah ranges, including the Wasatch. 
While there is the potential for locally heavy accumulations,
widespread heavy amounts are not expected through early Friday. 
WPC PWPF indicates only a few small areas, including the Wasatch,
for Day 1 (ending 12Z Friday) totals of 6-inches or more. 
However, as the upper low begins to slowly turn east, snow is
expected to continue across many of these same areas through
Friday into early Saturday, with additional light to moderate
accumulations likely, especially along the Mogollon Rim and the
southern Utah Mountains.  Day 2 (ending Saturday 12Z)
probabilities for additional accumulations of 6-inches or more are
highest 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 3 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 into the Nebraska Panhandle and much of central Colorado. 
This includes the urban I-25 corridor from Cheyenne through
Denver.  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.

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

Pereira