FOUS11 KWBC 060735
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 AM EDT Sun Apr 6 2025

Valid 12Z Sun Apr 06 2025 - 12Z Wed Apr 09 2025


...Northern Great Lakes...
Days 1-2...

A potent 500mb vorticity maximum tracking south from southern
Canada will provide modest upper level ascent when working in
tandem with a N-S oriented 250mb jet streak over the Great Lakes
Sunday evening. At lower levels, low pressure will develop beneath
the favorable diffluence and along a strengthening 850mb front. A
narrow band of moderate-to-heavy snow will ensue on the northern
periphery of the developing storm system as it tracks across
Michigan's Mitten late Sunday night and Monday morning. In addition
to the primary band of snow, CAA via brisk northerly winds will
trigger lake-enhanced snow showers over Michigan's U.P. and the
northern tier of Michigan's Mitten through Monday afternoon. As
daytime heating lessens late in the day, snow shower coverage
should diminish with only an unusually cold air-mass filtering in
behind the departing storm system. WPC probabilities show low-to-
moderate chances (30-50%) for snowfall totals >6" across the
northern-most portions of Michigan's Mitten. Similar probabilities
are present across much of the eastern Michigan U.P. for snowfall
>6" through Monday evening.

...Interior Northeast...
Days 2-3...

Following a minor snowfall accumulations from northern Pennsylvania
on east through the northern Appalachians Sunday night, the
primary low responsible for the snow over Michigan makes its way
east through southern Ontario Monday afternoon. A strong cold front
accompanying the storm system will escort rain showers along and
ahead of the front, but a dramatic temperature drop behind the
front will lead to a changeover to snow starting Monday afternoon
across the Lower Great Lakes, then over the northern Mid-Atlantic
Monday evening. It is still early to determine if there is a
notable snow squall threat, but the quick changeover from rain to
snow could cause a rapid reduction in visibilities for affected
areas.

By Monday night, the aforementioned 500mb vorticity maximum in the
"Northern Great Lakes" section will continue to foster exceptional
PVA ahead of the trough. The storm system will continue to
strengthen as it tracks across the St. Lawrence River Valley early
Tuesday morning and across northern New England later in the day
Tuesday. There is a compact TROWAL on the back side of the storm
that will foster a narrow deformation zone on the backside of the
storm. In addition, CAA on the backside will provide some lake-
enhanced snow Tuesday morning and into Tuesday afternoon. The storm
will race east over the eastern Canadian Maritimes Tuesday night
and snow will quickly taper off. WPC probabilities show an
expansive area of low-to-moderate chances (30-50%) for snowfall
totals >4" from the Tug Hill on east across the Green/White
Mountains and northern Maine. These locations also sport low chance
probabilities (10-30%) for localized snowfall amounts >6" through
Tuesday evening.

WPC probabilities for ice accumulations above 0.1" throughout the
CONUS are below 10%.


Mullinax




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