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Probabilistic Heavy Snow and Icing Discussion...UPDATED
NWS Weather Prediction Center College Park MD
405 PM EST Thu Dec 25 2025

Valid 00Z Fri Dec 26 2025 - 00Z 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 1-2... Maximum impact level from WSSI: Moderate

Quasi-zonal flow continues to direct a plume of moisture=20
originating from the West along the US/Canadian border=20
leading to WAA- driven snow over the MN Arrowhead into the U.P. of
Michigan. With cold sub-32F sfc temps over parts of MN/WI/Lower MI
at precip onset tonight, some freezing rain is likely with minor=20 accumulations over MN/WI. WPC probabilities for at least 4 inches=20
of snow are low to moderate (20-60%) over the Keweenaw Peninsula
into the eastern U.P.=20

Into D2, shortwave will push through northern Lower MI with its=20
sfc reflection over IN/OH and the 850mb low moving through BUF. The
sfc low will weaken as it approaches the Appalachians, getting too
far behind the mid-level shortwave, and ultimately jumping into=20
the Atlantic by 12Z Sat. From Friday to Saturday morning, a variety
of ptypes are expected over the region (central Appalachians/Mid-=20
Atlantic to the Northeast). The stubborn cold surface air will hold
tight over Lower MI and especially into the Laurel Highlands in=20
western PA where significant freezing rain is possible. WPC=20
probabilities of at least 0.10" icing are high (>70%) from central
to southeast MI, including Detroit, as well as into western=20
PA/western MD. 40 to 70% probabilities of at least 0.25" icing=20
exist over southeast MI down through northwest PA into the Laurel=20
Highlands. Light icing is likely on either side of this zone of=20
maximum probabilities -- on the south side along the I-66 corridor=20
(DC) and into eastern WV. To the north/northeast, deeper cold air=20
at the surface will allow for sleet to be a dominant ptype over=20 central/eastern PA with up to an inch of sleet possible.=20

To the north, from central NYS through northeast PA into the=20 Catskills/Poconos and to the NYC Metro area, an axis of moderate to
locally heavy snow is increasingly likely, driven by the stronger=20
height falls at the nose of the incoming 130kt jet. Beginning to=20
see numerical guidance fall in line on the axis of greatest=20
snowfall potential with the NAM shifting further south compared to=20
its placement at 00z. Rest of the dynamical guidance is keying on=20
the area from southern NY state down through the Lower Hudson to=20
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.=20=20

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=20
into the NYC Metro/Long Island to the south. Probabilities for at
least 6" are now between 50-70% 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=20
progressive, combination of higher SLRs and upslope could yield=20
more than 8 inches of snow into the southern Catskills where areal
average maxima is currently positioned with some deterministic
indicating >10" on their outputs.

Fracasso/Kleebauer

...California/Sierra Nevada...=20
Day 1... Maximum impact level from WSSI: Extreme

*** Heavy Snow Continues on the Sierra Nevada through Tonight ***

The final round of widespread heavy snow arrives early this evening
to the northern Sierra Nevada then works its way down the length=20
of the Sierra Nevada through the overnight. Expect a few hours of=20
2-3"/hr rates (per the 12Z HREF) above the snow level of 5000ft=20 (north/central Sierra) to 6000ft (southern Sierra) with an=20
additional 12-18" overnight.

Moderate snow showers continue into Friday evening with snow=20
levels dropping to 4500ft. The upper trough which had been offshore
finally shifts east to the Great Basin Friday night, cutting off=20
Sierra snow by 12Z Saturday.

Far northern CA ranges (Shasta Siskiyou/Klamath/etc) can expect=20
two more rounds of heavy snow: this evening above 4000ft and early
Friday down to 3500ft. Snow impacts to I-5 near Mt Shasta are=20
likely Friday. Some moderate snow linger Friday night before=20
ending by 12Z Saturday.=20

For SoCal, snow levels remain around 7000ft through Friday morning=20
and most of the additional precip. Snow levels do drop below=20
6000ft Friday afternoon with some 1"/hr rate potential around Big=20
Bear Lake into the evening before tapering off.

Jackson

...Pacific Northwest, Great Basin and Rockies...=20
Days 1-3... Maximum impact level from WSSI: Moderate to Major

Deep low pressure off CA will continue to infuse moisture across=20
the West with a separate trough pushing down the BC coast Friday=20
and over the northern Rockies Saturday providing a final focus for=20 precipitation and ending the active pattern.=20

Ongoing snow over the Cascades tapers off this evening with=20
moderate to locally heavy snow for the length of the Cascades=20
Friday and Friday night with snow levels dropping on the WA=20
Cascades from 3000ft to 1000ft and over the OR Cascades to 2000ft.=20
Day 1.5 snow probs for >8" are 50-90% on the WA/OR Cascades=20
including for the Snoqualmie and Santiam passes.

The next round of moisture from CA arrives into the northern=20
Rockies this evening with prolonged moderate to heavy snow until=20
the cold frontal passage Friday night. Snow levels drop from=20
6000/7000ft to 3000/4000ft through this time leading to increasing=20
travel impacts. Day 1.5 snow probs for >8" are 50-80% over the=20
Sawtooths, northern ID/western MT ranges, western WY ranges, the=20
higher central NV ranges, and the Wasatch.

The progression of the cold front is notable with the Day 2.5 snow
probs for >8" limited to the Wasatch and 50-80% for northern and=20
western CO Ranges.

Jackson



...Winter Storm Key Messages are in effect for California (1) and
the Great Lakes/Northeast (2) as linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-g-GW__WozhP2rpufLMN5NvBEkkjdn8JWvmleGJtVDvie= KanJvcNGyGIHQAVOvIb69relAxzfxlMKZa2cZavzv-P0Oo$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!-g-GW__WozhP2rpufLMN5NvBEkkjdn8JWvmleGJtVDvie= KanJvcNGyGIHQAVOvIb69relAxzfxlMKZa2cZavVPwJrv8$=20



$$

=3D =3D =3D
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