FOUS11 KWBC 270803
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
303 AM EST Thu Feb 27 2025

Valid 12Z Thu Feb 27 2025 - 12Z Sun Mar 02 2025


...Northeast...
Day 1...

The first in a pair of winter storms tracks through the Northeast
today. NAEFS shows a sub 1004mb low tracking through the eastern
Great Lakes that is below the 10th  percentile. This low is also
directing a narrow >500 kg/m/s IVT towards New England that is
above the 90th climatological percentile. As anomalous moisture is
directed towards the northern Appalachians, a sufficiently cold
air-mass located over New England will support periods of snow,
particularly in the northern Appalachian ranges. With low-level WAA
and 290k isentropic glide aloft, periods of snow will be ongoing
from the Adirondack on east through the Green and White Mountains
this morning. As low pressure tracks into the Champlain Valley
around midday, snow will track into the northern two-thirds of
Maine with a wintry mix just north of the Maine coastline. The
storm will race northeast into the St. Lawrence Valley of southern
Quebec by Thursday evening with a dry slot moving in aloft that
effectively shuts off most accumulating snowfall beyond 00Z Friday.
WPC probabilities show low-to-moderate chances (30-50%) for
snowfall >6" in the peaks of the Green and White Mountains. Most
snowfall totals >500ft in elevation that are not in the Green and
White Mountains are most likely to see anywhere from 1-4" of
snowfall through Thursday afternoon. The WSSI does show a swath of
Minor Impacts from southern VT and central NH on east through the
southern half of Maine. Residents in these areas could contend with
hazardous driving conditions, particularly in areas with complex
terrain.


...Upper Great Lakes through the Northeast...
Days 2-3...

An unusually strong clipper system diving southeast from southern
Canada will head for the Upper Great Lakes on Friday. The storm
will reside beneath the diffluent left-exit region of a 90-100 knot
500mb jet streak, while also sporting an unusually strong NWrly IVT
that surpasses 300 kg/m/s on the western flank of the Clipper. The
low-level circulation at 850mb is also rather potent with heights
that are below the 0.5 climatological percentile by 18Z Friday
according to NAEFS. This equates to what would be a "front-end
thump" of heavy snow late Thursday night across the Minnesota
Arrowhead, then across the Michigan U.P. and far northern Michigan
Friday morning where the best 850mb FGEN ensues. Just north of the
850mb FGEN is where snowfall rates of 1-2"/hr are possible for
several hours. A dry slot and warming boundary layer should limit
snowfall over the Michigan U.P. and northern Michigan Friday
afternoon. As the storm heads east though, additional snow is
likely on the back side of the storm as low-level CAA over Lake
Superior increases Friday evening. Snow should taper off by
Saturday morning in the Upper Great Lakes. WPC probabilities show
moderate-to-high chances (50-70%) for snowfall totals >6" in the
MN Arrowhead with similar chances for >8" in the Keweenaw
Peninsula, the, Huron Mountains, and eastern Michigan U.P..
Localized amounts approaching a foot are possible closer to Sault
Ste. Marie, MI.

The storm continues its march east into southern Ontario Friday
evening with the same method of producing periods of heavy snow as
far east as the Tug Hill and Adirondacks of northern New York.
Unlike the Upper Great Lakes, however, the storm track is farther
north through the St. Lawrence Valley. WPC's Snowband Probability
Tracker, utilizing the 00Z HREF guidance, shows the potential for
1"/hr rates from the Tug Hill to as far east as the Green and White
Mountains Friday night. The dryslot and warming low level-
temperatures arrive Saturday morning with only northern Maine
likely to still see periods of moderate-to-heavy snow through rest
of the day Saturday. Snow should taper off throughout the Interior
Northeast by Saturday night. WPC probabilities show moderate-to-
high chances (50-70%) for snowfall >6" in the Tug Hill and
Adirondacks neighboring the Tug Hill through Saturday morning.


Mullinax


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