Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
235 PM EST Tue Mar 08 2022

Valid 00Z Wed Mar 09 2022 - 00Z Sat Mar 12 2022

...Western U.S....
Days 1-3...

Broad troughing across the CONUS will lead to cyclonic flow over
much of the West, with cooling mid-level temperatures and periodic
shortwaves leading to widespread mountain snow through the period.
The shortwave primarily responsible for heavy snow the next few
days will drop out of British Columbia D1 and into the northern
Great Basin on D2 while sharpening. This shortwave will deepen
further as it shifts into the Four Corners D3, and may cutoff from
the northern stream Friday morning, slowing over the Desert SW.
Jet level ascent will be modest through the period in response to
the LFQ of an approaching jet streak, and subtle RRQ diffluence as
the subtropical jet streak extends towards the Great lakes Friday.
This shortwave dropping southward will also drive a cold front
across the West, and snow levels are likely to drop from 3000-5000
ft ahead of the front, to 500-1000 ft or less behind the front.
Most of the snow is likely ahead of the front when snow levels are
on the higher end, so WPC probabilities for more than 6 inches are
confined to the higher terrain. On D1, WPC probabilities for more
than 6 inches are above 50% from the Cascades southeast through
the Uintas and Park Range of CO. On D2 the heavy snow sinks
southward, and WPC probabilities for 6+ inches becoming focused
over the Wasatch/Uintas of Utah and the CO Rockies. Heavy snow
shifts even further SE on D3 into the Sangre De Cristos and San
Juans. Storm total snowfall could reach 1-2 feet in some of the
higher terrain of UT and CO by the end of the forecast period.


...Central Rockies through the Upper Midwest...
Days 1-3...

An arctic cold front will sag southward across the middle of the
CONUS tonight through Thursday, serving as a low-level baroclinic
boundary upon which synoptic ascent will interact. This deep layer
lift will be produced via height falls/PVA ahead of a shortwave
ejecting from the Four Corners region around a broad positively
tilted trough, with downstream jet intensification leaving modest
upper diffluence across the Central Plains. The overlap of these
features with the low-level baroclinic zone will likely lead to
modest surface cyclogenesis in the lee of the Rockies and this low
will drop southeast while weakening. However, robust WAA ahead of
the wave will surge northward on an increasing LLJ out of the Gulf
of Mexico, and this will lead to intensifying isentropic upglide
at 285K-290K, with mixing ratios climbing to 2-3 g/kg during the
period of most intense ascent. This pronounced isentropic lift
combined with CSI potential within the west-to-east oriented fgen
band could produce snowfall rates of 1"/hr or more, although these
are likely to be in a narrow corridor embedded within a larger
area of moderate snowfall. Where this band sets up will likely
lead to the heaviest accumulations, and while guidance continues
to feature some latitudinal differences in the placement, it is
expected to be in the vicinity of the NE/KS border, with a local
maxima likely just NW of the KC metro area where moist advection
maximizes and the temporal duration of snowfall is extended. A
separate maxima of snowfall is likely where upslope flow behind
the front aids in ascent, and this is likely in the Laramie Range
and into the Cheyenne Ridge of SE WY.

WPC probabilities on D1-D1.5 are above 70% for 6+ inches in the
Laramie Range and the Cheyenne Ridge, where locally 12 inches of
snowfall is possible. Further east during the latter half of D2
and into D3, a stripe of WPC probabilities in excess of 40% for 6+
inches will extend along the NE/KS border and into far NW
Missouri. Locally, 10" of snow is possible, with the best chance
for this occurring near the MO/NE/KS intersection on D2.


...Northeast & Mid Atlantic...
Days 1-2...

A shortwave embedded within broad cyclonic flow across the CONUS
will lift northeast over the Ohio Valley and into New England
while an associated surface low lifts from the southeast to off
the New England coast. The primary longwave trough axis will
remain back across the Plains, but amplification of this trough D1
into D2 will lead to an intensifying jet streak arcing across New
England, and the favorable RRQ diffluence will overlap with height
falls and PVA to deepen the surface low, at least modestly, as it
skirts well south of New England by Thursday morning. Impressive
WAA ahead of the wave will help expand a shield of precipitation
northward, while also leading to a narrow but potent band of
mid-level frontogenesis lifting northward across the region. While
the WAA will eventually overwhelm the cold air to produce a snow
to rain scenario for the Mid-Atlantic and much of the coast,
moderate to heavy snow is likely to be the predominant p-type for
inland PA, Upstate NY, and much of New England. A burst of heavy
snow within the WAA/fgen band may produce tricky travel for the
I-95 corridor from Washington, D.C. to NYC, but snowfall
accumulations should be light and confined to elevated or grassy
surfaces, However, a longer period of heavy snow with rates of
0.5"/hr to 1"/hr should lead to plowable snowfall from the central
Appalachians through the Laurel Highlands, into the Poconos,
Catskills, Litchfield Hills, Berkshires, and Worcester Hills,
where WPC probabilities for 4+ inches are 10-30%. In the lower
elevations of southern and central New England, light
accumulations of less than 4 inches are likely.

Weiss