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QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
405 AM EST Wed Jan 8 2025

Valid 12Z Wed Jan 08 2025 - 12Z Sat Jan 11 2025

...Part 2/2...

...Great Lakes and Northeast... Day 1...

Broad upper low churning near Newfoundland and southeast Canada
will continue to help stream arctic air and shortwaves over the
Great Lakes through at least early Thursday. This will cause
additional lake- effect snows south and southeast of each of the
lakes in D1/Wednesday. Lake surface temperatures from GLERL for
Lake Michigan are around 45F/+6C, with the Arctic air moving over
the lake this evening expected to range between -12C and -15C at
850 mb. This will be ample instability to sustain
cellular convection within the lake-effect. WPC probabilities for
at least 4 inches of snow are generally ranging between 30 to 70
percent, with the highest probabilities occurring along much of the
immediate Lake Michigan shoreline in far western Michigan, around
Erie, PA where a strong band originating off of Lake Huron is
reinforced by the brief time the band is over Lake Erie, as well as
off the southeast end of Lake Ontario into the Syracuse area. By
D2/Thursday, high pressure moving overhead of the Great Lakes will
end the lake- effect from northwest to southeast until the next
round of light snow arrives from a central U.S. trough on D3.

...Rockies and West Texas... Days 1-2...

The arrival of Arctic air into the Southwest and Southern Plains
will set the stage for a much more significant and widespread
snowfall event as the vertically stacked low merges with a strong
shortwave by the D2 period on Thursday. Strong isentropic ascent
will allow for a period of snow showers later today into tonight.
Additionally, increasing moisture will overspread much of Texas as
upper level southwesterly flow increases in response to the upper
trough sharpening and lifting north. WPC PWPF values have over 70%
chance of 2 inches of snow across much of southern New Mexico
peaking over the Sacramento Mts, with lower probs (10-30%) over far
west Texas and nearby southern High Plains northward into New
Mexico. and far west Texas and up to 50% for 4 inches through the
D2/Thursday period for the Sacramento Mountains, with a 10 to 30%
chance of 4 inches over the adjacent Plains and into west and
north-central Texas and far southern Oklahoma. The most widespread
snow will be into D3/Thursday night as a more portent surface low
develops and quickly moves east, taking much of the Gulf moisture
with it, as well as any widespread precipitation.

Farther north, a shortwave moving out of Canada through Montana on
the northern side of the aforementioned longwave trough on
Wednesday will touch off some light to locally moderate snow over
much of the state what will punch into Wyoming and the Black Hills
tonight into Thursday. WPC probabilities for at least 4 inches of
snow are highest over the Little Belts, Gallatin Range, and into
the Bighorns, in the 70-90 percent range.


...Pacific Northwest and Northern Rockies... Day 3...

Shortwave entering the Pacific Northwest on Friday will spread high
elevation snow to the Cascades and Northern Rockies as it pushes
eastward and snow levels are expected to start around 4500ft and
fall to around 3000ft by the end of the forecast period. WPC
probabilities for at least 8 inches are between 40-70% for the WA
Cascades and northern ID mountains.

Snell


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

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

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