Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
326 AM EDT Tue Apr 8 2025

Valid 12Z Tue Apr 08 2025 - 12Z Fri Apr 11 2025

...Interior Northeast...
Days 1 & 3...

Low pressure tracking through the St. Lawrence River Valley will
direct its strong cold front east across the I-95 corridor this
morning. There could still be some remnant potent snow showers
early this morning, but additional snow showers may develop
throughout the interior Northeast and northern Mid-Atlantic due to
lingering low-level moisture and steepening low-level lapse rates.
Little accumulation from these snow showers is expected.

Farther north across far northern New York and northern New
England, snow on the northern flank of the storm and lake-effect
bands on the backside of the storm will result in accumulating snow
today and into Tuesday night. Gusty winds on the backside of the
storm will make for reduced visibilities, while the heaviest rates
are located across much of northern Maine, the White Mountains of
northern New Hampshire, and the Green Mountains of northern
Vermont. Snow will taper off by early Wednesday morning as the
storm system tracks towards Nova Scotia. WPC probabilities show
moderate-to-high chances (50-70%) for snowfall >8" in the Green and
White Mountains, as well as west-central Maine. Some localized
snowfall amounts approaching 12" are possible in west-central
Maine. Over northern New York, moderate chance probabilities
(40-60%) for >4" of snowfall are present in the Tug Hill and along
the
northern-most portions of the Adirondacks. The WSSI continues to
depict Minor Impacts across northern New England, suggesting some
hazardous travel conditions are possible anticipated through
Tuesday night.

By Thursday night, an amplifying upper trough over the Ohio Valley
will develop low pressure over the Carolinas. It will direct a
plume of moisture northward into the Northeast that could be
sufficiently cold enough to support mountains snow in parts of the
Interior Northeast. There remains a fair amount of uncertainty
regarding the QPF and if the boundary layer is also sufficiently
cold enough to support snow. At the moment, WPC probabilities due
show low chances (10-30%) for snowfall >2" in parts of the highest
elevations of the Adirondacks, Green, and White Mountains.


...Great Lakes...
Days 2-3...

A complex forecast for much of the Great Lakes from Wednesday into
early Thursday. As a 500mb shortwave trough approaches from the
west on Wednesday, it will generate modest upper-level divergence
at the same time as 850mb FGEN ensues over the Lower Great Lakes.
The GFS/CMC is stronger with the 850mb FGEN and southwesterly WAA
compared to the ECMWF. This means there is a more solidified area
of precipitation and better dynamic cooling in the GFS/CMC suite
along the northern flank of a developing wave of low pressure,
while the ECMWF is flatter and less supportive for snow. Even if it
does snow in the GFS/CMC solutions, marginal boundary layer and
surface temperatures will make it tough for snow to accumulate
efficiently. WPC probabilities are <10% for snowfall totals >2" for
the time being, but this setup will be closely monitored in future
forecast cycles.


...Northern Rockies, Cascades, and Olympics...
Days 1-3...

A series of shortwave troughs rotating east at the base of a
longwave trough over the northeast Pacific will impose upper-level
divergence and direct plumes of Pacific moisture at the
Northwestern U.S. mountain ranges through Thursday. Snow across the
Olympics and Cascades will continue today as an IVT topping 400
kg/m/s directs its best injection of the Pacific moisture at these
ranges this morning and into the afternoon hours. Meanwhile,
Pacific moisture will also spill over into the Northern Rockies
that results in measurable in mountains such as the Blue, Sawtooth,
Bitterroots, Absaroka, Teton, and Lewis Range. Snow should taper
off throughout the northwestern U.S. Wednesday afternoon, but look
for another round of high-elevation (generally above 5,000ft) snow
in the Olympics and Cascades Thursday night as another Pacific
disturbance tracks north towards British Columbia.

With a lack of a sufficiently cold/dry air-mass in place, look for
most snowfall accumulations >4" to be confined to the higher/more
remote peaks of the northwestern U.S. mountain ranges. Snowfall
accumulations >6" are most likely at elevations >4,000ft in the
Olympics and Cascades. Notable passes that could see measurable
snowfall include Snoqualmie (3-6") and Stevens (4-8") where
hazardous travel are possible. The snowfall in the Northern Rockies
will be light-to-moderate with 1-4" of snowfall most common. Some
peaks of the Lewis Range and Absaroka may eclipse 6" by the time
snow concludes on Wednesday.


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


Mullinax