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

Valid 00Z Thu Apr 10 2025 - 00Z Sun Apr 13 2025


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

As a wave of low pressure tracks east along a strengthening low-
level warm front into this evening, 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 this evening to help snow accumulate. Solutions have
trended towards little to no accumulating snow from southern
Wisconsin on east to southern Michigan and both northern Indiana
and Ohio. WPC probabilities show low chances (10-15%) for snowfall
totals >2" across southern Michigan, while most areas in the Lower
Great Lakes see a coating to 2".

A similar setup for light snow occurs over the Northeast mountains
tonight into Thursday. Mountain ranges such as the Catskills,
Adirondacks, and Berkshires could see between a coating to 3" of
snowfall through Thursday night, with WPC probabilities of 20-40%
for >2". A break in the snow arrives Friday morning before another
round of mountain snow potentially 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 shortwave 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. The GFS remains the
most amplified and westernmost solution, which eventually floods
the Northeast with above freezing temperatures even into the
highest terrain of the Northeast by Saturday. WPC preferred a
multi-model blend and the CMC/ECMWF/ECAIFS solution which keeps
colder air in place for the elevated terrain of the northern
Appalachians, as well as less QPF into northern New England due to
a more suppressed low track. In this scenario there is also a
potential for light freezing rain accretion across the southern
Green Mts, where WPC probabilities for >0.1" of freezing rain are
10-20%. For snowfall, WPC probabilities show 40-70% chances for >2"
in the higher terrain of the Catskills, Adirondacks, southern
Green, and White Mountains through Saturday evening. There also the
potential for accumulating snowfall throughout the central
Appalachians, but this area has more uncertainty and relies on a
combination of upslope flow and the position of the closed 500mb
low.


...Cascades to Northern Rockies...
Day 3..

Approaching negatively tilted upper trough approaching the Pacific
Northwest Friday night into Saturday won't have a typical strong
plume of moisture, but as the low begins to close off across
western MT by the end of the period decent upper divergence will
support light to moderate snow across parts of the Cascades and
Northern Rockies. Snow levels will be low across the Cascades
(<2,000ft) by the day on Saturday, but with precipitation mostly
scattered and tied to the terrain. Snowfall totals are expected to
remain around 2-4", with higher amounts above 7,000ft. For the
Northern Rockies, snow levels will vary from 5,000-6000ft in
northern ID and northwest MT to above 8,000ft to start for the
remainder of the Rockies before crashing by the end of the forecast
period across MT. WPC probabilities for at least 6" of snow are low
(10-30%) from the Salmon River Range through the southwest MT
ranges.



Snell/Mullinax