Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
257 PM EST Sat Jan 08 2022

Valid 00Z Sun Jan 09 2022 - 00Z Wed Jan 12 2022

...Great Lakes...
Days 1-3...

An amplifying shortwave will drop from Saskatchewan, Canada
southeast to the L.P. of MI and then across New England during
Monday. This shortwave will drive a strong surface cold front
southeast through the region, with robust CAA in its wake. Strong
CAA with 850mb temps dropping to -20 to -25C atop the still
relatively warm and open Great Lakes will produce an extended
period of heavy LES in the favored N/NW snow belts. On D1, the CAA
will only envelop Lake Superior, so increasingly unidirectional
north winds will produce heavy LES across the eastern U.P. where
WPC probabilities for 4 inches are moderate. However, the fast
translation of the trough and associated cold front will quickly
drive LES production downwind of the other lakes during D2, and as
inversion heights climb to 10,000 ft due to as high as 1000 J/kg
of instability, snowfall rates will become intense, especially
downstream of Lake Ontario where nearly ideal wind direction
combined with some effective fetch/additional moisture from Lake
Huron will overlap. Snowfall rates of 2"/hr seem likely, and WPC
probabilities on D2 are above 90% for 6 inches, with 2 feet
possible in the Tug Hill Plateau. WPC probabilities for 6 inches
are also high in the eastern U.P. on D2 where locally 10 inches is
possible, with several inches also likely downstream of Lake Erie,
just south of Buffalo. Additional light snow is likely the first
part of D3 before shortwave ridging advects into the region from
the southwest.


...Mid-Atlantic through central New England...
Days 1-2...

Cold high pressure centered over the Mid-Atlantic will slowly
retreat eastward in advance of a mid-level trough axis and
associated downstream divergence on Sunday. As this high retreats,
it will extend a surface wedge down into the Central Appalachians.
At the surface, a cold front will approach from the west beneath
the trough, with WAA ahead of it spreading precipitation northward
atop the cold surface temperatures. As 850mb temps climb above 0C,
and the DGZ, at least initially, lacks saturation, a period of
light to moderate freezing rain is likely from WV northeastward
into southern New England and upstate New York. Surface wet bulb
temperatures in the upper 20s will lead to high accretion
efficiency, at least for several hours, but the lack of any dry/NE
flow to maintain low wet-bulb temperatures should gradually cause
a reduction in efficiency and cause many areas to transition to
rain, especially in the Mid-Atlantic, with enough CAA behind the
front leading to light snow across New England. Despite this, WPC
probabilities for significant freezing rain have come up with this
iteration, and are now 10-30% for 0.25" in central and southern
PA, with high probabilities for 0.1" extending into the Catskills,
Mohawk Valley, Litchfield Hills, Berkshires, and southern Green
Mountains. Ice accretion of greater than 0.01" is likely along the
I-95 corridor from Washington, D.C. through Portland, ME as well.

Behind the front, the environment looks increasingly favorable for
some scattered intense snow squalls Sunday evening and Monday
across Upstate New York and northern New England. 0-2 km CAPE
rises to 200 J/kg coincident with intense low-level fgen and
climbing values of the snow squall parameter. There is some
concern that RH will be drying out rapidly behind the front which
could limit the snow squall potential, but the potential exists
for briefly heavy snow rates to cause travel disruptions on D2.

Weiss