FOUS11 KWBC 062030
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
330 PM EST Mon Jan 6 2025

Valid 00Z Tue Jan 07 2025 - 00Z Fri Jan 10 2025

...Mid-Atlantic...
Day 1...

Trailing mid-level shortwave behind the outgoing major winter=20
storm will pass quickly through the Mid-Atlantic early this=20
evening, spurring another inch or two of snow east of the=20
mountains. Over central WV, some upslope enhancement will help=20
squeeze out perhaps a few inches, with WPC probabilities for an=20
additional 4 inches of snow after 00Z around 30-50%. Snow will=20
taper off there by Tuesday afternoon.


...Great Lakes and Northeast...
Days 1-3...

A large, sprawling, and multi-pronged circulation over=20
southeastern Canada will send mid-level shortwaves into the eastern
Great Lakes and Northeast over the next few days, maintaining high
chances of at least light snow over the higher elevations (NY and=20
northern VT/NH) and also downwind of the Great Lakes in general=20
owing to the broad cyclonic flow.=20

For D1, a compact closed low near Montreal this evening will swing
through northern NY/VT overnight with some terrain enhancement=20
over the northern Adirondacks and into the Green Mountains. WPC=20
probabilities for at least 4 inches of snow tonight through Tuesday
are 50-80% there.

By D2, with already cold 850mb temps below -12C or so, a=20
reinforcing shot of cold Canadian air (via another short wave out=20
of Canada) will steepen lapse rates and reinvigorate lake effect=20
snow off the western Great Lakes, especially along the western=20
shore of Lower Michigan, and also off Lakes Erie/Ontario on NW=20
flow. WPC probabilities for at least 4 inches of snow D2 are=20
highest south of Muskegon right along the lake short, but will be=20
dependent on the fetch and trajectory of the band.=20

For D3, one last shortwave will push through the eastern Great=20
Lakes and New England, maintaining additional light snow off Lake=20
Ontario on NW flow and additional snow for the northern Adirondacks
and Green Mountains. WPC probabilities for at least an additional=20
4 inches of snow are moderate (40-70%) over these areas.


...Intermountain West, Rockies, and Southwest...
Days 1-3...

Broad height falls moving through the Great Basin tonight will=20
sharpen into a closed low over the lower CO River Valley late Tue.=20
With high pressure nosing down out of the northern Plains, upslope=20
snow will expand across the CO Front Range via an easterly low=20
level flow along with a relatively low DGZ. However, the snow=20
should not last too long as the upper low will likely move into=20
northwestern Mexico by the end of the period. This will help to=20
drag the snowfall southward as well through the Mogollon Rim,=20
Sangre de Cristos, Sacramento Mountains, etc. Models continue to=20
vary on QPF (and thus snow) over parts of the Southwest but at=20
least a large footprint of light snow is expected. For the D1-3=20
period, WPC probabilities for at least 4 inches of snow are >50%=20
over the Front Range into the CO Rockies, San Juans, and higher=20
elevations in AZ/NM above 8000ft or so.=20

Farther north, a shortwave moving out of Canada through Montana on
Wednesday will touch off some light to locally moderate snow over=20
much of the state that will push into Wyoming and the Black Hills=20
on Thursday. WPC probabilities for at least 4 inches of snow are=20
highest (>50%) over the Little Belts, Gallatin Range, and into the=20
Bighorns.


...Southern Plains...
Day 3...

As the aforementioned upper low closes off over the Southwest=20
Thursday and continues to dig into northwestern Mexico Friday it=20
will become anomalously deep (below the 0.5th climate percentile=20
per the NAEFS ESAT). Meanwhile, a separate shortwave rounding the=20
far eastern Pacific ridge is forecast to dive southward through=20
Utah and interact with this feature and spawn strong southwest flow
containing rich moisture and prominent upper divergence from an=20
increasingly buckled jet. Given the strong high situated to the=20
north over the Central Plains and a cold low-level airmass in=20
place, snow and mixed precipitation is expected over much of=20
western and north-central TX late Wed and through Thursday,=20
expanding eastward to the Ozarks by the end of the period. Thermal=20
uncertainty is high (as expected) due to the upstream players=20
(timing, depth, etc.) and the NBM ptype probabilities show a zone=20
of maximum uncertainty from near the Big Bend northeastward to=20
around TexArKana.=20

All ptypes are in play -- snow/sleet/freezing rain and plain rain=20
to the south -- and each will likely not be stagnant in location.=20
For now, the highest probabilities of snow lie on the northwest=20
side of the precipitation shield in the deeper colder air from the=20
Permian Basin across Northwest TX into North TX (near and northwest
of the D-FW Metroplex). There, WPC probabilities for at least 4=20
inches of snow are around 30-50%. To the southeast, within the zone
of maximum uncertainty, probabilitiesfor accumulating snowfall=20
decrease while probabilities for ice increase. Areas from near=20
Austin northeastwardthrough the Piney Woods into the Hill Parishes=20
of LA show the highest chance of at least 0.1 inches of ice=20
accumulation (30-60%).


This system has prompted the issuance of a new set of Key Messages
which are linked at the bottom of the discussion.

Fracasso/Snell


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

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late=
stKeyMessage_2.png__;!!DZ3fjg!_p-d5kX8NzvPiea0SkbIvk3YnMjHKOh2q0s4iASxMHzCr=
TEx8epFDhVUmnjbsdroCOxm3zPaNswlrn58foeDVnjrYAg$=20

$$

=3D =3D =3D
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