Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
438 PM EDT Tue Apr 19 2022

Valid 00Z Wed Apr 20 2022 - 00Z Sat Apr 23 2022

...West Coast to the Northern Rockies...
Days 1-3...

A large, closed, mid-level low is forecast to slowly move east
toward the Pacific Northwest late Wednesday into Thursday as a
130kt jet sinks southward and eastward into the Great Basin.
Several embedded lobes of vorticity swing through across northern
CA into southern OR beneath a broad area of upper diffluence and
co-located with the best moisture plume axis. Significant heavy
snow is likely for the CA ranges including the Sierra which could
see 2-day storm totals between 1-2 feet for the highest peaks. The
other northern CA ranges and southern OR Cascades are likely to
see several inches to perhaps a foot as the cold front moves
through the region and lowers snow levels in its wake. By Day 3,
system will translate across the Rockies as additional snow falls
over northeastern Nevada and across Yellowstone and western
Wyoming. WPC probabilities for at least 6 inches are high (above
70 percent) over the higher elevations above 7000ft.

...Northern MN...
Day 1...

A strong and compact closed mid-level low will track along the
U.S./Canadian border tonight and into Wednesday as its associated
occluded front push through the northern Plains into the Upper
Midwest. Warm air advection ahead of the approaching wave will
work with increasing moisture streamed northward from the Gulf to
allow for a quick shot of precipitation Wednesday. The strong
southerly flow will offset dynamic cooling for most areas, except
across northern MN toward the Canadian border and the Iron Ranges
of the Arrowhead along the north shore of Lake Superior. This is
where local enhancement due to moist upslope flow will provide the
potential for higher snow totals, but this will be fighting
against the higher sun angle during the afternoon which may limit
accumulations. HREF probabilities do show potential for 1-2"/hr
rates, so this may allow for more robust accumulation in some
areas. The latest WPC probabilities for 4" range from 20-30
percent over much of northeastern MN to near 70-80 percent along
the north shore areas. Between Grand Portage and Grand Marais,
probabilities for 6" or more are 50-70 percent.


The probability of significant icing of at least 0.25" is less
than 10 percent.


Fracasso/Taylor