Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
254 PM EDT Sun Mar 20 2022

Valid 00Z Mon Mar 21 2022 - 00Z Thu Mar 24 2022

...Utah and Rockies onto the Southern Plains...
Days 1-2...

A longwave trough moving through the Great Basin tonight will
sharpen into a closed low across the Desert Southwest late tonight
and then eject into the Southern Plains Monday night while slowly
beginning to fill. While the primary impulse embedded within this
trough will weaken, reinforcing shortwave energy diving down from
Canada will maintain the amplitude of this trough through D2.
During this evolution, pronounced upper jet streaks will intensify
in response to the amplifying trough, and as the downstream jet
streaks couple, the overlap of this enhanced ventilation for
ascent combined with height falls/PVA will allow a lee cyclone to
intensify as it shifts northeast. Downstream of this low, warm and
moist advection will intensify as noted by 850mb winds exceeding
50 kts out of the Gulf of Mexico. This will drive an impressive
theta-e ridge northward into a TROWAL, which will combine with
upslope flow into the Southern Rockies and High Plains D2 to
enhance snowfall.

Moderate to heavy snow is likely D1 from the WY ranges southward
through the CO Rockies, the San Juans, and Sangre De Cristos where
WPC probabilities for more than 6 inches are high, and local
maxima will likely exceed 8 inches in the higher terrain. However,
the heaviest snow is likely D1.5 through D2.5 in the Raton Mesa
where the best and longest overlap of ascent and moisture drive
WPC probabilities for more than 6 inches to above 80%, and
isolated totals over 12 inches is likely.

Further to the south and east, guidance continues to suggest some
banding potential on the overlap of the LFQ of the subtropical jet
streak and sharpening deformation axis Monday night across the
TX/OK panhandles and into western KS. At this time WPC
probabilities for significant snowfall are limited, but do show a
5-10% for locally 4+ inches of snowfall as heavy rates dynamically
cool the column after an initial period of rainfall.


...Northern Plains through the Great Lakes...
Days 2-3...

A shortwave moving along the Canada/U.S. border will shift
eastward through ND/MN D2 before weakening, but will be replaced
by secondary shortwave energy dropping out of Manitoba as a
complex upper trough develops across the Upper Midwest. During
this period, a zonally oriented jet streak downstream of the
primary trough axis will shift east, placing increasingly
favorable RRQ diffluence for ascent across the region. A surface
low lifting northward out of the Southern Plains will move towards
Lake Michigan by the end of the forecast period, and east of this
low a warm front and associated pronounced moist advection will
surge northward into the Great Lakes. This WAA will likely expand
the precipitation shield, and while low-level thermals will be
marginal, there is likely to be an area of moderate to heavy snow
along the international border, with a secondary area of mixed
precipitation in the Great Lakes.

For the snow areas, WPC probabilities are high for more than 4
inches from central MN eastward to the eastern U.P. of MI, with a
local maxima across the Arrowhead of MN where upslope flow into
the Iron Ranges will maximize snowfall, aided by moisture from
Lake Superior. Locally, more than 10 inches of snow is likely
here. In the U.P. a secondary maxima is expected as well with
locally more than 6 inches likely. Surrounding these areas, a
larger swath of more than 4 inches is possible from near
International Falls, MN through Green Bay, WI, with some moderate
accumulations also possible along the Coteau de Prairies.

Further to the northeast, moderate accumulations of freezing rain
are likely as the WAA overruns the cold surface air into the
western and central Great Lakes. WPC probabilities for 0.1" of
accretion are above 40% both D2 and D3, with locally in excess of
0.25" of accretion possible in the eastern U.P. and northern L.P.
of MI.


Weiss