Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 PM EDT Thu Mar 24 2022

Valid 00Z Fri Mar 25 2022 - 00Z Mon Mar 28 2022

...Upper Midwest/Great Lakes/Central Appalachians...
Days 2-3...

A shortwave trough in south-central Canada will strengthen into a
potent closed low over Lake Erie Saturday morning. Latest 12Z GFS
shows 500mb heights are as low as 2.5 standard deviations below
normal over Ohio. 850mb temperatures as cold as 2 standard
deviations below normal rushing over Lake Superior will trigger
lake effect snow showers with heavy snowfall rates likely within
these bands. Closer to the Ohio Valley and the central
Appalachians, abnormally cold temperatures aloft combined with
peak heating in late March will foster steep low level lapse
rates. A ~110 knot 500mb jet streak over central Illinois
positioning its left exit quadrant atop the upper Ohio Valley and
central Appalachians will promote vertical ascent within the
atmospheric column as well, giving rise to the potential for snow
squalls tracking through these regions. Add in a brisk upslope
flow component into the central Appalachians and snowfall rates
will be heavy at times early Saturday morning and throughout much
of Saturday.

Latest 12Z HREF probabilities indicate a 20-40% chance for
snowfall rates exceeding 1" per hour between 06-12Z Saturday. 3km
NAM model soundings between 12-18Z Saturday in eastern WV also
showed up to ~250 J/kg MUCAPE available, suggesting similar
snowfall rates may continue into the daytime hours. Snowfall rates
should diminish Saturday night and into Sunday in the central
Appalachians as the best forcing moves east, but continuous
upsloping NW flow will keep periods of snow in the forecast into
Sunday morning. Latest WPC probabilities of >4" of snowfall on
Saturday range between 50-90% in eastern WV with a 20-30% chance
for totals exceeding 8". Farther north, lake effect snow off Lake
Erie could lead to locally heavy snow in northwest PA and western
NY on Saturday. WPC probabilities show a 20-30% chance for snow
totals exceeding 4" Saturday with similar probabilities just
downwind of Lake Ontario near the Tug Hill Plateau on Sunday.

...Northeast...
Days 1-2...

An upper level low tracking northeast through the Ohio Valley this
afternoon will track into the eastern Great Lakes tonight while a
surface low strengthens off the coast of Maine. This is in
response to upper level diffluence beneath the right entrance
quadrant of a jet streak over eastern Quebec tonight. High
pressure in the Canadian Maritime is providing a CAD signature at
low levels over northern New England, which combined with mild
southerly flow aloft will result in an icy overrunning
precipitation event. Latest WPC freezing rain probabilities show a
corridor of 40-50% of freezing rain accumulations greater than a
tenth of an inch. Farther north, colder air and a strengthening
700mb front will prompt a band of heavy snow across northern
Maine. The HREF Snowband Probability Tracker (SPT) does contain
some model members that contain over 1"/hr snowfall rates between
08-18Z Friday. The uncertainty in snow totals lies in the
uncertainty of boundary layer conditions and a quickly encroaching
dry slot in the 700-400mb layer Friday morning. In general though,
the closer to the northern Maine/Canada border, the better the
chances for receiving heavy snowfall accumulations. Latest WPC
probabilities do show a narrow area of 50-70% chance for snowfall
exceeding 4" in far northern Maine. Snowfall is expected to
conclude Friday afternoon as the primary wave of low pressure
tracks north of Nova Scotia.


Mullinax