Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 AM EDT Wed Apr 9 2025

Valid 12Z Wed Apr 09 2025 - 12Z Sat Apr 12 2025


...Great Lakes & Interior Northeast...
Days 1-2...

A fast approaching upper-level trough producing modest PVA aloft
at the same time as the diffluent left-exit region of a 120kt jet
streak moves in over the Great Lakes Wednesday afternoon and
through Wednesday night. As a wave of low pressure tracks east
along a strenghtening low-level warm front, a swath of
precipitation along the warm front and on the northern flank of the
storm will be capable of producing periods of snow. The setup
continues to feature very marginal boundary layer temperatures,
making it essential for dynamic cooling and the transition to snow
after sunset Wednesday evening to help snow accumulate. The wide
ranging solutions in guidance include little to no snow or as much
as several inches from southern Wisconsin on east to southern
Michigan and both northern Indiana and Ohio (showcasing the
complexities of the setup detailed above). WPC probabilities show
low chances (10-30%) for snowfall totals >2" across southern
Michigan, while most areas in the Lower Great Lakes see a coating
to 2" throughout the Lower Great Lakes.

A similar setup for light snow occurs over the Northeast mountains
Wednesday night into Thursday. Mountain ranges such as the
Catskills, Adirondacks, and Berkshires could see between a coating
to 2" of snowfall through Thursday night. A break in the snow
arrives Friday morning before another round of mountain snow
arrives late Friday into Saturday.


...Northern & Central Appalachians...
Day 3...

As the upper-level trough over the Ohio Valley deepens Thursday
night, excellent upper-level divergence via PVA ahead of an
embedded shortave disturbance will spawn a strengthening area of
low pressure in the Mid-Atlantic. Out ahead of the upper trough is
an IVT >400 kg/m/s that will deliver copious amounts of moisture
into the northern Mid-Atlantic and Northeast Friday and into
Saturday. While there is some residual sub-freezing air in the
Northeast, there is only enough to support snow in the more
elevated terrain of the central and northern Appalachians.
Elevations above 2,000ft are most favored for snowfall, but some
areas as low as 1,000ft in elevations could see rain transition to
snow Friday night. This is a sensitive setup given the time of year
with lack of sub-freezing temps and dynamic cooling being
necessary to support heavier snowfall rates. WPC probabilities show
10-20% chances for snowfall >2" in the tallest peaks of the
Catskills, Adirondacks, Green, and White Mountains through Saturday
morning.


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


Mullinax