Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
318 AM EST Mon Jan 24 2022

Valid 12Z Mon Jan 24 2022 - 12Z Thu Jan 27 2022

...Upper Midwest/Great Lakes/Northeast...
Days 1-3...

Broad and expansive cyclonic flow over much of Canada into the
northeastern 1/3 of the CONUS will persist through the next 3 days
with fast-moving/periodic embedded shortwaves moving through the
flow. This will support episodes of light to occasionally moderate
snow to the northern tier with lake effect snow off the Great
Lakes. Clipper system currently moving through the Upper Midwest
this morning will slip eastward across Lower Michigan and the St.
Lawrence River Valley Day 1 with generally 1-3" in most places.
SLRs of 15-20:1 should capitalize on QPF ~0.10-0.20" especially
between Lower Michigan and western PA/NY. N to NNW flow behind the
system will rejuvenate LES downwind of the Upper Lakes Day 1 where
favored areas may see in excess of six inches. By day 2, high
pressure will slide from North Dakota to the Corn Belt which will
relax the Lake snows as winds weaken. On Day 3, light warm
advection snow will spread eastward ahead of a Canadian cold front
with light amounts around an inch or so.  

WPC probabilities of at least 4 inches of snow is highest in
favored Lake belt regions of the U.P. and western Lower Michigan
as well as NW PA and ESE from Lake Ontario (south of the Tug
Hill).


...Rockies and western Plains...
Days 1-2...

Compact mid-level shortwave will drop south-southeastward on the
west side of the Rockies Day 1 as a surface cold front stalls over
Montana but sinks southward and southwestward through the Plains
toward the Front Range. A lack of moisture initially will confine
snowfall accumulations to mainly under 4 inches across Montana for
Day 1 outside some higher mountains. By Day 2, the combination of
upper diffluence and upslope flow will help focus stronger lift
over the terrain and foothills of the CO Front Range with
additional higher totals across western Kansas near the
intersection of modest UVVs mostly into the DGZ with frontogenesis
in the ~650-700mb layer per some CAM guidance. QPF trend has been
a bit wetter which could translate into several inches of snow in
a relatively brief period over western Kansas on Tuesday. Snowfall
threat will quickly spread into eastern NM and eventually the TX
Panhandle as the cold front sinks southward and southwestward. By
Day 3, light snow may spread eastward into the Red River Valley
and southward toward I-20 but with amounts mostly an inch or less
with less favorable thermal profiles.

WPC probabilities for at least 4 inches of snow are greatest on
day 1 across south-central Montana then reach moderate to high
levels on day 2 for western Kansas and into northeastern New
Mexico.


For days 1-3, the probability of significant icing is less than 10
percent.


Fracasso