Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
435 AM EDT Wed Mar 11 2020

Valid 12Z Wed Mar 11 2020 - 12Z Sat Mar 14 2020


Days 1-3...

...Pacific Northwest/Northern Rockies...
A northern stream trough and associated cold front dropping south
across the northwestern U.S. is expected to produce light to
moderate snows along the northern Rocky Mountain Front in
northwestern Montana on Wednesday - with WPC PWPF showing high
probabilities for accumulations of 8-inches or more across the
higher terrain.

A more significant storm is expected to develop across the region
Friday and Saturday.  Models show an amplifying shortwave digging
south along the along the British Columbia coast Thursday to early
Friday, with a closed low developing as the system reaches the
Washington coast by late Friday.  This will bring an increasing
threat for heavy high elevation snows across the Olympics and
northern Cascades - with WPC PWPF showing high probabilities for
accumulations of 8-inches or more across the higher terrain.  This
system is forecast to bring much colder air into the region,
lowering snow levels below the passes in the western Washington. 
Meanwhile, a strong cold front is forecast to push south through
the northern Rockies and Intermountain West.  This along with
moisture spreading east of the Cascades will support the potential
for impactful snows over northeastern Washington and northern
Idaho into northwestern Montana.  Strong southeasterly winds along
with a weak low level wave is expected to raise the threat for
moderate to locally heavy amounts east of the Divide into the High
Plains of central Montana on Friday into early Saturday.  

...Southwest/Southern and Central Rockies...
A closed low is forecast to remain along the coast of Southern
California through Thursday night before ejecting inland as an
open wave across the Southwest through the Four Corners region on
Friday.  This is expected to bring heavy snows into portions of
the central and southern Rockies, especially along the San Juans,
where WPC PWPF shows high probabilities for accumulations of a
foot or more for the Day 3 period (ending 12Z Sat).  Locally heavy
accumulations are also possible across the southern Utah ranges,
as well as the Sangre de Cristo mountains.

...Central Plains...
As the leading energy associated with the weakening low lifts
across the Rockies, snows are expected to develop east of the
mountains over the central Plains, with light to moderate snows
expected to develop across eastern Colorado, Kansas, Nebraska and
southern South Dakota.  Heaviest amounts through Day 3 are
expected to center across southwestern into central Nebraska,
where WPC PWPF shows higher probabilities for accumulations of
6-inches or more.

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

Pereira