Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
356 AM EDT Fri Mar 25 2022

Valid 12Z Fri Mar 25 2022 - 12Z Mon Mar 28 2022

...Upper Midwest/Great Lakes/Central Appalachians...
Days 1-3...

A complex interaction of mid-level features with a surface wave
and cold front will produce heavy Lake Effect Snow (LES), upslope
snow, and convective snow showers across the region through Sunday.

A shortwave lifting out of the Ohio Valley this morning will be
quickly replaced by a more potent impulse digging out of Alberta
to close off near Chicago this evening. This closed feature is
then likely to continue to dive rapidly southeast into the
Mid-Atlantic Saturday before filling and lifting off to the
northeast Sunday morning. This feature will combine with modest
LFQ diffluence within an upstream jet streak diving out of the
Pacific Northwest to produce large scale ascent across the region.
With only marginal moisture in place (PWs of -1 standard deviation
below the climo mean), this overlap of ascent will generally
result in a swath of light to moderate snow from eastern MN
through the Great Lakes and Ohio Valley, and into the Mid-Atlantic
and Northeast. However, there are likely to be three areas of
enhanced snowfall embedded within this larger swath of
precipitation.

The most impressive snowfall is likely in the favored W/NW snow
belts off the Great Lakes as CAA becomes impressive behind a wave
of low pressure and the accompanying surface cold front. Strong
CAA in the wake of this front will steepen the low-level lapse
rates to super-adiabatic levels, and with lake temperatures
beginning to warm, inversion depths are progged to climb above
5,000 ft. These inversions are not exceptionally impressive, but
the instability off the lakes should enhance local ascent, which
despite modest SLRs should lead to an extended period of LES. For
D1, heavy snow is likely in the western U.P. and Bayfields
Peninsula where WPC probabilities for more than 4 inches of snow
are as high as 50%. The heavy LES shifts eastward D2 to focus
downstream of Lake Erie, especially into the Chautauqua Ridge
where moist flow will efficiently upslope to increase snowfall.
WPC probabilities on D2 for more than 4 inches are above 50% in
this region. Heavy snow may persist on D3 downstream of Lake Erie,
while increasing downwind of Lake Ontario, especially into the Tug
Hill plateau. 2-day snowfall east of Lake Erie and Ontario may
exceed 10 inches in a few places.

Additional heavy snow is likely D2 into D3 along the spine of the
Central Appalachians of WV and into the SW portion of the Laurel
Highlands. In this area, W/NW winds behind the front will drive
moist ascent Saturday, leading to periods of heavy snowfall before
the DGZ begins to dry out late Saturday into Sunday. This snowfall
could be enhanced by increasing instability as the primary
shortwave and PV anomaly swing overhead on Saturday. WPC
probabilities for more than 4 inches are above 80% D2, and total
snowfall Sat-Sun could reach 12 inches in isolated locations of
the higher terrain of WV.

Finally, the potent PV anomaly swinging from MN through the
Mid-Atlantic will be accompanied by increasing instability within
the elevated cold pool noted by 500mb heights approaching -3
standard deviations from the climo mean according to NAEFS
ensemble tables. As this upper low pivots overhead, it will be
accompanied by increasing low-level fgen and surface instability
which could reach 250 J/kg. Forecast soundings indicate a deeply
saturated column with lapse rates greater than moist adiabatic
(indicative of a MAUL), and the high-res guidance is in good
agreement that convective snow showers will develop this aftn
through Saturday evening. While the coverage of these snow showers
may be scattered, the snow-squall parameter is forecast as high as
4, which suggests that isolated snow squalls could be embedded
within this convective snowfall. Despite snow accumulations that
are likely to be minimal as this activity drops southeast from the
Upper Midwest this evening through the Ohio Valley and into the
Central Appalachians/Mid-Atlantic late Saturday, brief snowfall
rates of more than 1"/hr combined with gusty winds could produce
hazardous travel due to limited visibility.


...Northeast...
Day 1...

Sharp 5H shortwave will eject northeast from the Ohio Valley and
over Upstate New York today before shifting into the Canadian
Maritimes by Saturday morning. While this primary shortwave stays
well inland, modest height falls and an increasing upper
ventilation within the RRQ of a poleward streaking jet will drive
slow intensification of a surface low moving over Downeast Maine
today. WAA ahead of this low will expand precipitation into Maine
while a wedge of Canadian high pressure gradually retreats to the
east. This will continue an overrunning scenario with periods of
sleet/freezing rain likely across parts of northern and central
Maine. North of the mixed precipitation, a burst of heavy snow is
likely, generally confined to Aroostook County, as the WAA
impressively upglides to produce a burst of snowfall that could
reach 1"/hr this morning according to the SPC snow band prototype
tool. This heavy snow should be of relative short duration
however, and WPC probabilities for more than 4 inches of snow are
about 20-40%.


Weiss