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FOUS11 KWBC 010834
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
334 AM EST Thu Jan 1 2026

Valid 12Z Thu Jan 01 2026 - 12Z Sun Jan 04 2026

...Eastern Maine...=20
Day 1...

Potent upper trough will swing across New England today, with an
embedded vorticity maxima lifting into the Canadian Maritimes
Thursday night. The evolution of this vorticity max combined with
at least the distant LFQ of a southeast diving upper jet will allow
a surface low to deepen as it tracks across Northern New England,
intensifying more rapidly in response to a negative tilt of the
upper trough this evening into Canada. While in general this=20
system will be progressive, an inverted trough positioned west of=20
the primary low will rotate across eastern Maine as the low shifts=20
northward, leading to a longer duration of moderate to heavy=20
snowfall rates (30-50% chance of 1"/hr). This will result in a=20
swath of moderate snowfall accumulations for which the WPC
probabilities indicate has a moderate chance (50-70%) of exceeding
6 inches, highest across Downeast Maine.


...Great Lakes...
Days 1-3...

An arctic front passing east of the Great Lakes early this morning
will leave impressive CAA in its wake, while cyclonic flow asserts
itself across the region. This cyclonic flow will be secondary
enhanced late Thursday night into Friday as another shortwave
passes through the flow, leading to renewed CAA before shortwave
ridging develops by the end of the forecast period.

While this arctic front will maintain a snow-squall risk through
early this morning into New England and the Mid-Atlantic (for which
Key Messages remain in effect, linked at the bottom of this
discussion) the primary hazard becomes widespread heavy lake effect
snow (LES) in the favored W/NW snow belts. The most intense LES
will likely begin late tonight as 850mb temperatures plummet to as
low as -15C to -20C, across lakes that, while they have cooled,=20
are mostly ice-free. This will lead to impressive SBCAPE as high
5000-1000 J/kg to support a long duration 1-2+"/hr LES event,
especially downwind of Lakes Erie and Ontario due to upstream
connections. The heaviest accumulations D1 and D2 are expected
across the Chautauqua Ridge and along//just barely south of the=20
Tug Hill plateau before shifting a little south into D2. WPC
probabilities are high (>90%) for 6+ inches in these areas D1,
continuing east of Lake Ontario D2. Locally 2-4 feet of snow is
possible east of Lake Ontario before LES wanes during D3. Downwind
of the other Great Lakes, WPC probabilities D1 feature a moderate
risk (50-70%) for 6+ inches in the eastern U.P., but this wanes
quickly during D2.


...California through the Central Rockies...=20
Days 1-3...

A deep trough in the subtropical Eastern Pacific will lift=20
NNE through the central CA coast early today before crossing the=20
Sierra Nevada and into the Great Basin by Friday morning. The
primary shortwave within this trough will crest an expanding ridge
(amplifying downstream of a more intense trough over the Pacific)
and drop into CO and the High Plains Friday morning/aftn.,=20
As the trough moves inland, snow levels on the Sierra Nevada will=20
fall to around 7500ft this afternoon, bringing heavy snow until=20
precipitation ends this evening. Farther east, and continuing
downstream of this trough/impulse, snow levels will remain elevated
at 7000-8000 ft, but precipitation falling as snow will spread
across much of the Great Basin and Four Corners at the higher
elevations. WPC probabilities D1 for 6+ inches of snow reach above
70% in the Sierra, and locally as high as 70% in portions of the
Wasatch and CO Rockies. Precipitation will linger through D2 across
the Four Corners terrain, but with generally a waning trend.

Then on D3 a more pronounced surge of precipitation spreads onshore
CA once again as a deep trough amplifies offshore, resulting in
impressively amplified southerly flow. This will push moisture
onshore as IVT exceeds 500 kg/m/s (>80% chance). Once again snow
levels will be elevated within the accompanying WAA, reaching as
high as 8000 ft into the Sierra (although much lower around 6000 ft
across the Shasta/Trinity region). The pronounced moisture will
result in heavy snow again above these levels, and with SLR
expected to be low, it will be an impactful snowfall due to snow
load. WPC probabilities D3 are high (>90%) for more than 6 inches
across these mountains, with locally more than 12 inches possible
(30-50% chance) in the Sierra.


...Columbia Basin and Gorge...
Day 1...

Increasing southerly mid-level flow over the Pacific Coast will
spread moisture northward, aided by a weakening shortwave lifting
from CA into the northern Great Basin. As this moisture spreads
into the Pacific Northwest, it will overrun a slowly retreating
ridge of high pressure, manifesting with easterly winds draining
into the Columbia Basin/Gorge to maintain cold surface air. This
setup is favorable for light freezing rain with modest accretions
as reflected by WPC probabilities that reach as high as 70% for 0.1
inches of ice. Although amounts are generally light, impacted=20
travel is likely tonight into Friday morning due to slippery=20
roadways.


Weiss


...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!4KcpeRfEaE90L2aFopU7nqHmEr2kAB4kKifoH1AxvdJX1=
x1YD-GsTigUG8uJqvwrOLksvrurJKgrhdg4n79dPyZCvaE$=20



$$

=3D =3D =3D
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