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QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
148 AM EST Fri Dec 26 2025

Valid 12Z Fri Dec 26 2025 - 12Z Mon Dec 29 2025

*** Continued Heavy Snow on the Sierra Nevada through Friday ***

*** Heavy Wintry Mix tonight through Friday night from the Great
Lakes through the Northeast and Mid-Atlantic ***

...Great Lakes to Northeast... Days 1 & 3...
Maximum impact level from WSSI: Moderate

Current UA analysis pin-points our shortwave that be involved in
the next winter focused disturbance over the northern and eastern
CONUS. Forecast is for the shortwave trough to push through
northern Lower MI with a sfc reflection developing over IN/OH this
morning. Major player in the forecast evolution will also be the
attendant 850mb low which will migrate over Lower MI, cutting east
to BUF leading to persistent southwesterly flow within the upper
portion of the boundary layer. The sfc low will weaken as it
approaches the Appalachians, getting too far behind the mid- level
shortwave, and ultimately jumping into the Atlantic by 12Z Sat.

From Friday to Saturday morning, a variety of ptypes are expected
over the region (central Appalachians/Mid- Atlantic to the
Northeast) thanks to the WAA regime progged between 925-800mb. The
stubborn cold surface air will hold tight over Lower MI and
especially into the Laurel Highlands in western PA where
significant freezing rain is possible. WPC probabilities of at
least 0.10" icing are high (>70%) from central to southeast MI,
including Detroit, as well as into western PA/western MD. 40 to 70% probabilities of at least 0.25" icing exist over southeast MI down
through northwest PA into the Laurel Highlands. Light icing is
likely on either side of this zone of maximum probabilities -- on
the south side along the I-66 corridor (DC) and into eastern WV. To
the north/northeast, deeper cold air at the surface will allow for
sleet to be a dominant ptype over central/eastern PA with up to an
inch of sleet possible.

To the north, from central NYS through northeast PA into the
Catskills/Poconos and to the NYC Metro area, an axis of moderate to
locally heavy snow is likely, driven by the stronger height falls
at the nose of the incoming 130-135kt jet. 00z model suite is in
agreement on the axis of heaviest snowfall aligning over the area
from Central and Southern NY state down through the Lower Hudson
to NYC and 50-75 miles on either side seeing at least 4" with >6"
becoming a greater likelihood around the Catskills into the Lower
Hudson Valley to the north of NYC.

WPC probabilities for at least 4 inches of snow are still >50% in
a zone bounded between I-890/Rt 17/I-476 to the west, the southern
Adirondacks on the north side, Berkshires/I-91 to the east, and
into the NYC Metro/Long Island to the south. Probabilities for at
least 6" are now between 50-90% for that area of central NY state
down through southern NY, including the Catskills/Lower Hudson/NYC
corridor south and east of I-88. Though the system will be
progressive, combination of higher SLRs and upslope could yield
more than 8 inches of snow into the southern Catskills where areal
average maxima is currently positioned and latest WPC probabilities
for >8" now upwards of 40-70%.

On D3, another surface cyclone will intensify and move northeast
through the Upper Midwest and Great Lakes. Ensemble means show a
rapid CAA pattern within the northwest side of the cyclone leading
to snowfall breaking out across northeastern MN into northern WI
and the Michigan U.P. Best chance for at least 4" of snow lies over
the western U.P. due to lake effect threat kicking in downwind of
Lake Superior. WPC probabilities for >4" are now between 50-90%
across all of the central and western U.P. with the highest
probabilities across the Iron Range over into the Keweenaw Peninsula.

Kleebauer

...California/Sierra Nevada... Day 1...
Maximum impact level from WSSI: Extreme

*** Heavy Snow Continues on the Sierra Nevada through this morning***

Final push of moderate to heavy snowfall forecast across the Sierra
Nevada today with the heaviest likely to occur this morning before
slowly waning as our AR event finally comes to an end. Prior,
expect heavy snow rates between 2-3"/hr at times leading to
additional accumulations between 1-2ft above 9000ft MSL. WPC
probabilities for >12" are still between 50-80% for much of the
northern and central Sierra Nevada with the highest probabilities
co-located with the area near Mammoth up to just south of I-80.
Storm totals will approach 4-6ft or more after the full event is
complete leading to significant impacts to travel even after the
event has completed.

Kleebauer

...Pacific Northwest, Great Basin and Rockies... Days 1-3...
Maximum impact level from WSSI: Moderate to Major

Deep low pressure off CA will continue to infuse moisture across
the West with a separate trough pushing down the BC coast Friday
and over the northern Rockies Saturday providing a final focus for precipitation and ending the active pattern.

Moderate to locally heavy snow for the length of the Cascades will
occur through today into early Saturday morning with snow levels
dropping on the WA Cascades from 3000ft to 1000ft and over the OR
Cascades to 2000ft. Snow probs for >8" are 50-90% on the WA/OR
Cascades including for the Snoqualmie and Santiam passes.

Moisture from the leading edge of the AR from the Pacific will
continue to maintain a prolonged moderate to heavy snow forecast
until the cold frontal passage later this evening. Snow levels
drop from 6000/7000ft to 3000/4000ft through this time leading to
increasing travel impacts. Snow probs for >8" are 50-90% over the
Sawtooths, northern ID/western MT ranges, western WY ranges, the
higher central NV ranges, and the Wasatch.

The progression of the cold front is notable with the Day 2 snow
probs for >8" limited to the Wasatch and 50-80% for northern and
western CO Ranges.

Jackson/Kleebauer

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

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

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_2.png

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