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

Valid 00Z Tue Jan 25 2022 - 00Z Fri Jan 28 2022

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

A weak clipper system will eject through New England Tuesday
leaving broad and expansive cyclonic flow across the eastern CONUS
in its wake. While this system will be fast moving and weak, it
could produce several inches of snow in the higher terrain,
reflected by WPC probabilities for 4+ inches as high as 40% in the
White Mountains of NH and in far Downeast Maine.

The more significant impact from this will be persistent lake
effect snow (LES) in the favored W/NW belts downwind of the Great
Lakes. 850mb temps crashing to below -20C will produce steep lapse
rates and deep inversion depths supporting of intense LES across
the U.P. of MI, the eastern shore of Lake Michigan, and into the
Tug Hill Plateau of Upstate New York. Snowfall rates could exceed
1"/hr at times aided by high SLRs in the cold airmass, and WPC
probabilities are high for more than 4 inches in these regions on
D1, with locally more than 6 inches possible. Continued LES is
likely D2 but mid-level flow will gradually back as shortwave
ridging advects from the west. This will mostly shut off the LES
over Lake Superior, but will allow for several more inches on the
eastern shore of Lake Michigan and, more impressively, into the
Chautauqua Plateau east of Lake Erie where WPC probabilities for
4+ inches are 20-30%. Another shortwave rotating through the flow
D3 will bring more favorable LES conditions once again, but this
time in a more W/SW orientation, at least initially. WPC
probabilities D3 are low for 4+ inches of additional accumulation,
highest in the NW L.P.


...Northern to Central Rockies and High Plains...
Days 1-3...

A surface cold front will dig southward across the Central Plains
tonight before surging into Texas while banking into the Front
Range on Tuesday as a broad longwave trough envelops the eastern
half of the CONUS. Within this trough, a shortwave will dive
southward out of Alberta, Canada and amplify across the Central
Rockies/Four Corners Tuesday evening, while a zonally oriented jet
streak ejects into the Ohio Valley leaving RRQ diffluence over
KS/CO. The combination of upslope flow behind the front, height
falls and mid-level divergence downstream of the shortwave, and
upper diffluence will provide ample ascent to produce moderate to
heavy precipitation across the higher terrain from southern MT
through the Front Range of CO including the Palmer Divide where
WPC probabilities for 4+ inches are above 50%. Additionally on D1,
a swath of heavy snow is likely to develop within a region of
enhanced mid-level frontogenesis behind the front extending into
parts of western KS where snowfall rates of 1"/hr are possible at
times, and WPC probabilities for more than 4 inches are high, and
locally more than 6 inches is possible.

By D2 /Tuesday night into Wednesday/ the shortwave digs further
south placing the most intense ascent over NM where height falls
and continued RRQ upper diffluence persist. This synoptic lift
combined with moderate upslope enhancement and periods of robust
frontogenesis will drive heavy snow across northern New Mexico and
WPC probabilities for more than 4 inches are above 70%, highest in
the Sangre De Cristos where locally more than 8 inches is
possible. Further to the east into the TX Panhandle, as the wave
begins to open, a band of deformation may shift eastward producing
some mixed rain and snow, transitioning to snow during more
intense precipitation through wet-bulb cooling. Light to moderate
snowfall is likely within this band, which is reflected by WPC
probabilities for 2+ inches as high as 40% extending almost to the
OK border.

The leading shortwave kicks out and weakens Wednesday night, but
is followed quickly by some sheared shortwave energy dropping once
again out of Alberta and through the Rockies. Mid-level divergence
and some renewed upper diffluence should spread pockets of light
to moderate snowfall from the Northern Rockies through the Sangre
De Cristos, but additional accumulation is likely to be just a few
inches.



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


Weiss