Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 AM EST Mon Jan 17 2022

Valid 12Z Mon Jan 17 2022 - 12Z Thu Jan 20 2022

...Mid Atlantic through the Interior Northeast...
Day 1...

A significant low pressure moving into PA this morning will
continue to lift rapidly northward into Quebec by late tonight.
This low will continue to deepen as it moves through Upstate NY,
with intense deep layer ascent provided through strong WAA, upper
diffluence, and sharp height falls. A mature TROWAL wrapping
cyclonically around the low will continue impressive moist
advection into the Northeast today, with the overlap of this
moisture and ascent producing heavy precipitation.

Well inland from the coast and in the terrain of Northern New
England, this will manifest as heavy snow and WPC probabilities
for more than 6 inches are high in the White and Green Mountains,
with well over 12 inches likely near Mt. Washington. Further east,
a burst of heavy snow with rates of 1"/hr or more are possible,
but a quick changeover to sleet and then rain will limit
accumulations outside of the higher elevations. Further west, and
west of the surface low across Upstate NY heavy snow accumulating
to more than 6 inches is likely within a pivoting deformation axis
that will lift northward over far western PA, the Lakes regions of
NY, and into the Adirondacks. Locally 10" of additional snowfall
is possible where the most impressive banding occurs.

As the low pulls away, NW flow across the Great Lakes will produce
several inches of LES downwind of Lake Erie and Ontario, while NW
flow into the terrain of WV and the Laurel Highlands of PA will
produce upslope flow from which WPC probabilities are modest for
more than 6 inches.


...Upper Midwest through the Great Lakes...
Days 2-3...

A clipper system will dive southeast out of Alberta and then move
along and just south of the US/Canada border into the Great Lakes
before lifting off into Ontario D3. While this system is fast
moving and has limited total forcing associated with it, some
modest WAA will enhance moisture and squeeze out a swath of
moderate to heavy snow across northern MN, northern WI, and the
U.P. of MI where WPC probabilities are high for 4+ inches and
locally more than 6 inches is possible. However, guidance has
trended down a bit overnight with the available moisture and hence
snowfall accumulations. As this wave pulls east of the Great Lakes
on Wednesday /D3/ it will leave cyclonic flow and CAA in its wake
sufficient for some LES in the favored N/NW snow belts, especially
downwind of Lake Superior and Lake Michigan. The airmass is quite
cold behind this system, driving the DGZ down to the surface or
even below in some areas, so SLRs will not likely be too extreme.
Still, moderate LES is likely, and WPC probabilities on D3 are
moderate for more than 4 inches across portions of the U.P., as
well as near Traverse City, MI, and in the Tug Hill Plateau.

Weiss


~~~ Key Messages for Winter Storm Affecting the Eastern U.S.
January 16-17 ~~~

-- Heavy snow rates greater than 1â€/hr are possible along and
just west of the Appalachians today and Monday. Significant
impacts to travel are likely.

-- Ice accumulation will expand northward through the interior
Mid-Atlantic states this evening, creating hazardous travel
conditions.

-- Heavy snow is expected along the Appalachians into the interior
Northeast. Significant snow totals are likely across much of West
Virginia northward through western Pennsylvania/New York, and the
higher elevations of New England. This could result in dangerous
travel and scattered power outages.

-- Along the Atlantic coastline, strong winds and coastal flooding
are likely. Some locations may reach moderate flood levels, with
inundation affecting some coastal roads and structures.