Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
213 PM EST Fri Jan 07 2022

Valid 00Z Sat Jan 08 2022 - 00Z Tue Jan 11 2022

...Pacific Northwest to the Central Rockies...
Days 1..

Modest trough will push eastward across the Intermountain West
while waves of embedded vorticity rotate through it. Height falls
and weak PVA will be accompanied by RRQ diffluence to provide
synoptic deep layer ascent across the region. PWs across the
region will remain around +1 to +1.5 standard deviations above the
climo mean, but will wane with time through late D1, aided by the
advance of a mid-level ridge following closely in the wake of the
aforementioned trough. This will produce minimal snowfall coverage
during the last day of this active pattern. WPC probabilities for
6 inches are high only in the highest terrain of the CO Rockies,
including the Park Range, the WA Cascades, and parts of the
Northern Rockies.


...Great Lakes...
Days 2-3...

An impressive shortwave will drop across the Great Lakes late D2
into D3 leaving amplified troughing in its wake. Sharp cyclonic
flow will develop behind this trough and accompanying cold front.
850mb temps plummet to the coldest of the season, falling below
-20C, and this will occur atop still relatively warm lake
temperatures. The setup looks favorable for an extended period of
heavy LES in the favored N/NW snow belts beginning Monday night
and persisting through Tuesday. Local soundings suggest intense
unidirectional flow and inversion heights over 10,000 ft with more
than 500 J/kg of instability atop the Lakes. While the high-res
guidance will likely handle this better once the forecast gets
into those high-res windows, but impactful heavy snow is becoming
more likely D3. WPC probabilities are currently more than 50% for
6+ inches in parts of the U.P., and downwind of Lake Erie and
Ontario. Locally well in excess of 12 inches is possible.


...Northeast...
Day 2...

Cold high pressure over the Mid-Atlantic Saturday will gradually
give way to the east ahead of an approaching trough, but maintain
a wedge from New England down through the Appalachians. Modest
return flow ahead of the mid-level trough and associated surface
front will spread WAA/precipitation into the area Sunday morning.
The 850mb temps will climb well above 0C, but surface temps and
surface wet-bulb temps will likely remain below freezing, at least
initially, across much of the Northeast. This will produce a
period of freezing rain across parts of the Mid-Atlantic into
southern New England, with the longest duration of ZR likely in
central PA and across the Catskills and Berkshires were WPC
probabilities are as high as 50% for 0.1". Elsewhere, light
freezing rain accreting to a few hundredths of an inch is becoming
more likely along the I-95 corridor from Washington, D.C. to
Boston, MA.

Weiss