Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
408 AM EDT Fri Apr 15 2022

Valid 12Z Fri Apr 15 2022 - 12Z Mon Apr 18 2022

...Central West Coast region to the Northern Rockies...
Days 1-2...

Th persistent upper level low centered just offshore the Pacific
Northwest gradually becomes strung out along the US/Canada border
over the next day or so, reinforced by a fast approaching compact
shortwave trough that moves into central/north-central California.
This will maintain a cold and unsettled pattern across the region
through the upcoming weekend. The favorable forcing for ascent
over the region combined with the approaching moisture plume will
lead to widespread precipitation, including heavy mountain snow,
initially over northern California on D1 then into portions of the
Northern Rockies on D2. Lower snow levels will help drive some
higher snow totals across northern California on D1 where the
latest WPC probabilities for 8 inches are moderate to high. For
D2, heavy snow lingers for the Sierra as well as Northern Rockies,
specifically the Sawtooths in ID. Combined day 1 and 2 totals
could exceed a foot for much of the Sierra and northern California
higher elevations as well as the Sawtooths in ID.

...Northern Plains...
Days 2-3...

Fast moving shortwave energy undercutting the closed low
positioned off the Pacific Northwest accelerates both pieces of
energy eastward through the Rockies toward the Northern Plains
days 2-3. The northern shortwave opens up as it approaches the
Northern Rockies while an associated surface low develops over
portions of Wyoming and tracks eastward through North Dakota. As
this taps into better moisture and lift, widespread snow is
expected from northern/northeast MT through much of ND then into
portions of northern MN. The guidance this cycle continued to have
some latitudinal spread where the 00Z NAM shifted northward along
with the GFS to some degree. The CMC and 00Z ECMWF offer a more
southern track, but this is still a jog to the north. As a result,
the best signal for higher QPF / strong frontogenetical forcing
has shifted northward. Given some of the spread, the WPC QPF and
WWD leaned toward a consensus of the ensemble means which is a
very slight northward adjustment from continuity. This supports
the potential for advisory to near warning level snow amounts. The
latest WPC PWPF shows 50 to 70 percent probabilities of 4 inches
while the PWPF shows a 10-20 percent probability of totals on D3
exceeding 8 inches.



For Days 1-3, the probability of 0.10 inch or more of ice is less
than 10 percent.

Taylor