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FOUS11 KWBC 291843
QPFHSD

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

Valid 00Z Tue Dec 30 2025 - 00Z Fri Jan 02 2026

*** Major Winter Storm for the Great Lakes and Northeast=20
 Transitioning to Lake-Effect Snow Today ***

...Great Lakes/Northeast...
Days 1-3... Maximum impact level from WSSI: Major to locally=20
Extreme

The powerful cyclone responsible for today's heavy snow and
blizzard conditions over the Great Lakes and significant icing in
northern New England will become trapped beneath a strongly -AO/-NAO
regime that keeps prolonged cyclonic-flow over the Great Lakes and
Northeast to close out 2025 and open 2026. Strong WAA over=20
northern New England combined with a sub-freezing boundary layer=20
will keep ice in the forecast a bit longer over the White Mountains
and much of ME. By tonight, brisk W-NWrly over the Great Lakes=20
along with some lingering low-level CAA will keep single-band LES=20
streamers going tonight and through Tuesday downwind of Lakes Erie=20
and Ontario. From the Michigan U.P. on south through the western=20
and northern sections of Michigan's Mitten, numerous LES showers=20
will lead to additional minor-to-moderate snowfall totals with=20
gusty winds causing reduced visibilities in affected areas.

By Tuesday night, a weak trough passing over the Great Lakes will
produce some minor snowfall from WI on east through MI's Lower
Peninsula and over northern IL/IN/OH. This trough will shift
low-level winds over the eastern Great Lakes from NWrly Tuesday
evening, to westerly overnight Tuesday, then WSWrly by Wednesday
morning. This wind shift is in response to a potent 500mb shortwave
over Ontario that will race southeast over Lake Ontario by New
Year's Eve night. This upper trough will not only act as to
reinvigorate the LES machine downwind of Lakes Erie and Ontario,
but it will also be associated with the leading edge of a potent
Arctic front. Incoming CAMs and deterministic guidance is showing
exceptional jet dynamics aloft when combined with relatively steep
low-levle lapse rates to support snow squalls New Year's Eve
afternoon and evening. Both the NAM and GFS snow squall parameters
are showing squall potential from MI's Lower Peninsula on south and
east through eastern OH, western and central PA, and into Upstate=20
NY. The NAM doesn't rule out these snow squalls potentially=20
reaching the I-95 corridor early New Year's Day. This is naturally=20
very poor timing for residents on the roads given the rapid=20
reductions in visibilities and potential accumulations on roads.=20
Those heading out on the roads New Year's Even Night and New Year's
morning should keep a close eye on the forecast in the coming=20
days.=20

In addition to snow squalls, strong upslope ascent into the central
Appalachians is likely to cause heavy snow New Year's Night and
into early New Year's Day morning. Lingering cyclonic flow will
keep LES showers in the forecast across the typical snow belt
locations of the Great Lakes through New Year's Day. Through the
afternoon of January 1, WPC's 72-hour snowfall probabilities show
high chances (>70%) for snowfall totals >18" along the Chautauqua
Ridge in northwest PA and western N, including towns just south of
Buffalo. Localized amounts topping 30" somewhere along the Ridge=20
in western NY are possible, as evident by WPC's probabilities for=20
>30" totals generally between 10-30%. Just east of Lake Ontario,=20
WPC probabilities show moderate-to-high chances (50-70%) for=20
snowfall totals >18" with Oswego County, NY the most likely=20
epicenter. Note the WSSI does show Major Impact potential for the
Syracuse metro area Tuesday and into Tuesday night. Even far=20
northwest OH sports moderate chances (40-60%) for snowfall totals=20
>12". Farther south, the central Appalachians that consist of the=20
Potomac and Laurel Highlands have high chances (>70%) for 3-day=20
snowfall totals topping 8" through the afternoon of January 1,=20
2026. Otherwise, most snowfall across northern MI and the eastern=20
MI U.P. are likely to range between 4-8" and more of a 2-6" range=20
over western MI and northern IN.


...Southeast New Mexico/Guadalupe Mountains...=20
Day 1... Maximum impact level from WSSI: Moderate

The ENErly upslope flow coupled with 700mb WAA/FGEN via SWrly flow
over southern NM and west TX will keep periods of snow ongoing in=20
parts of the Sacramento and Guadalupe Mountains for a little=20
longer today before tapering off this evening. A couple more inches
of snow are forecast and the WSSI continues to depict Minor to=20
locally Moderate Impacts this afternoon in southeast NM and west TX
north of I-20.


...Sierra Nevada...=20
Day 3... Maximum impact level from WSSI: Minor

An unusually deep upper-tough in the tropical East Pacific will
direct a slug of anomalous moisture (above the 99.5 climatological
percentile per ECMWF) at CA on Wednesday and continue into
Thursday. Southerly flow would foster upslope enhancement into the
peaks of the Transverse Ranges and the Sierra Nevada in this case.
However, the lack of a continental polar air-mass over the West
will make any snowfall likely confined to the >9,000ft remote peaks
of the Sierra Nevada. Even despite the healthy slug of moisture,
low SLRs will also make for a heavy/wet snow that will be less
efficient to accumulate in boundary layer conditions so mild. WPC
probabilities show...

Mullinax



...Winter Storm Key Messages are in effect. Please see current=20
 Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late=
stKeyMessage_1.png__;!!DZ3fjg!5qU-SWL0FMuQl4dvXgDp3enNHlEFr08VyNW76WrZTAq5d=
rxMbZCok3Roua7BXu_kSntlo4JSilNmu64NtaWIuNxNq0E$=20



$$

=3D =3D =3D
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