FOUS11 KWBC 290718
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
218 AM EST Mon Dec 29 2025

Valid 12Z Mon Dec 29 2025 - 12Z Thu Jan 01 2026

*** Major Winter Storm for the Upper Midwest/Great Lakes and
Northeast Transitions to Lake-Effect Snow Today ***

...Great Lakes/Northeast... Days 1-3...
Maximum impact level from WSSI: Major to locally Extreme

Mature cyclone with a central pressure in the mid 970s mb this
morning will be near peak intensity, with direct affects lessening
through the day. Comma-head/TROWAL snows over Michigan will
transition to lake-effect snow by this afternoon as the parent low
continues through Ontario into Quebec. In its wake, winds will
still be strong, creating blowing and drifting snow even where none
may be falling. Blizzard warnings remain in effect over parts of
the Upper Midwest this morning and will continue over the U.P. of
Michigan through the day. An additional 8 inches of snow after 12Z
is likely (>50% probability) over at least the eastern half of the
U.P. With cyclonic flow around the low continuing today, the lake
effect machine will kick in downwind of Lake Michigan (this
morning) and Erie/Ontario later this afternoon/evening. An
additional shortwave will fly in from Canada through the Great
Lakes TUesday afternoon into Wednesday, adding a little more lift
to the region. Westerly to WNW flow into the central Appalachians
will also promote modest snows for eastern WV, western MD, and into
the Laurel Highlands. With the strong flow over the lakes, some
multi-lake connection could support long-lived streamers well
inland. Yet another shortwave out of Canada later Wednesday into
Thursday will help maintain the lake effect off Erie/Ontario
through the end of this forecast period.

Three-day total snowfall will be highest in NW PA and in the
Chautauqua Ridge as well as into central NY near Syracuse and into
the Tug Hill Plateau. Winds will sometimes be transient and
sometimes rather stationary, and totals may vary widely on a given
day. WPC probabilities for at least 8 inches of snow through 12Z
Thursday are >50% over western Lower Michigan, northeastern OH into southwestern NY, over the central Appalachians, and into central
NY to the Tug Hill. Within these regions, WPC probabilities for at
least 18 inches of snow are >50% over NW PA and SW NY and near
Syracuse toward Watertown (Oswego, Pulaski, etc.).

In the Northeast, the advancing warm front then cold front will
flush out the entrapped cold surface air which has resulted in
significant freezing rain accumulations so far. A little more icing
of a tenth or so is possible just after 12Z before a quick
changeover to rain then back to snow post-FROPA.

...Southeast New Mexico/Guadalupe Mountains... Day 1...
Maximum impact level from WSSI: Moderate

A cold front plunging southward has brought in much colder
temperatures to the region. ENE sfc flow behind it beneath moisture
advecting eastward from the Pacific will lead to snow over the
Guadalupe and southern Sacramento Mountains Monday. With 700mb WAA
via SWrly flow over southern NM and west TX colliding with
northerly 700mb winds over the High Plains, mid-level FGEN could
support some modest snow especially over the terrain. WPC
probabilities of at least 4 inches of snow are >50% in the
mountains, with lighter accumulations eastward to the TX border.

...Sierra Nevada... Day 3...

Incoming moisture from the Pacific will reach the central and
southern Sierra Wednesday into Thursday morning. Snow levels are
quite high -- 9000 to 10,000ft -- and accumulations will be light
even at the highest elevations.

Fracasso

...Winter Storm Key Messages are in effect. Please see current
Key Messages below...

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png

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* Origin: Capitol City Online (21:1/175)