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

Valid 12Z Tue Apr 19 2022 - 12Z Fri Apr 22 2022

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

Ongoing storm system this morning will continue to push inland the
Pacific Northwest with the eastward push of the cold front. Snow
levels falling to around 3000 ft will keep the highest snow totals
confined to the OR Cascades, Sierra but also further east across
the Northern Rockies around Yellowstone N.P. WPC probabilities for
6 inches are as high as 30-40 percent. A brief reprieve is then
expected for the first half of day 2 before another, stronger and
longer duration storm system arrives. A large, closed mid-level
low is expected to slowly move east toward the Pacific Northwest
late Wednesday into Thursday. Several embedded lobes of vorticity
swing through across northern CA into southern OR and this is
where the best moisture plume axis sets up. 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 and the WPC probabilities for 6 inches are
60-80 percent late in the day 2 through day 3 period.

...Northern MN...
Day 2...

A strong closed mid-level low will track along the U.S./Canadian
border Wednesday with its associated surface low beneath the
closed low occluding to a secondary trough positioned across
Minnesota. 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
north/northwest of Duluth across 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. The latest WPC probabilities for 4" range
from 20-30 percent away from the Lake to near 70-80 percent along
the north shore areas while between Grand Portage and Grand
Marais, probabilities for 6" or more reach 50-60 percent.

...Northeast...
Day 1...

Low pressure early this morning crossing Long Island will continue
to move northward through New England through the late morning and
lifting into Canada by this afternoon. Radar imagery this morning
shows widespread precipitation ahead of the low center with a
deformation band pivoting northwest of the low center across
portions of PA and central NY where snow rates between 1-3"/hr
will continue for a few more hours. The heaviest snow will wind
down this morning south to north as the low lifts away but in its
wake, modest cold air advection and northwest flow will set the
stage for upslope snow showers downwind of the Lakes as well as
against the Adirondacks and Greens and even across the central
Appalachians upslope in WV. This is where the greatest WPC PWPF
signals for additional 2-4" exist with localized higher amounts up
to 6" likely during the day 1 period.


The probability of significant icing across the CONUS is less than
10 percent.


Taylor