FOUS11 KWBC 080812
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
312 AM EST Sun Dec 8 2024

Valid 12Z Sun Dec 08 2024 - 12Z Wed Dec 11 2024

...Northeast...
Day 1...

Quick-moving system crossing from Ontario into Quebec before 12Z
will continue eastward across northern Maine this morning and early
afternoon before moving into Atlantic Canada. Light snow is
forecast after 12Z this morning for the Adirondacks and northern
New England, with a bit higher amounts over eastern Maine where
snow will eventually taper off later this afternoon. WPC
probabilities for at least 4 inches of snow today after 12Z are
20-40% over far eastern Maine.

Day 2...

The next winter storm to affect the region comes from a
combination of a shortwave over the Ohio Valley and a northern
stream upper low over southern Canada, both acting in concert to
coax a moisture plume northward from the Gulf of Mexico on WAA. A
mix of some freezing rain on the southern side (northeast PA
northward through NYS and also over parts of western New England)
and snow on the northern side (north of I-90) may cause some minor
impacts on Monday. WPC probabilities for at least 4 inches of snow
are not higher than 10 percent, but are moderate (40-70%) for at
least 2 inches over northern NH into western ME.

Day 3... Yet another system will start to affect the Northeast as
the pattern becomes more amplified in the East. Through 12Z Thu,
strong WAA should scour out most of the cold air over the region,
but interior Maine may see some light icing very early Wednesday
with much more precipitation into D4.


...Pacific Northwest/Northern Rockies...
Days 1-2...

Second part of the two-part system will affect the NW today,
pushing moisture into a much colder environment. Moderate to heavy
snow at the higher passes may continue to cause moderate impacts
this morning before the snow starts to taper off from west to east
this afternoon. WPC probabilities depict high chances (>70%) for at
least 8 inches of snow above about 3,500ft while the more remote
areas above 5,000ft likely receive an additional 12"+ of snowfall.

Moisture will continue east of the Cascades across to the Rockies
as the cold front has moved well past the Divide. WPC probabilities
for >8" of snow are over the higher terrain including the
Bitterroots, Lewis Range, Blue Mountains, and into the Little Belt
Mountains in central Montana, the Absarokas in southern Montana,
and the Tetons of western Wyoming. Snow will continue into D2
farther east over the Black Hills where probabilities of at least 4
inches reach 60-90%.


...Northern Minnesota and northeastern North Dakota...
Day 1...

Low pressure over southern Saskatchewan this morning will move ESE
toward northern ND/MN this evening and overnight, lifting its warm
front through the region. While precipitation may start out as
snow along the Canadian border, mid/low-level WAA may promote an
area of freezing rain for portions of eastern North Dakota into
Minnesota this morning, with several hundredths of an inch of ice
possible after 12Z. Closer to the Canadian border, a colder column
supports light to modest snowfall, with the heaviest snow occurring
with the initial WAA over northern Minnesota (esp the Arrowhead,
which will be enhanced by easterly flow off Lake Superior). WPC
probabilities for at least 4 inches of snow are >50% across much of
the northern part of MN, with higher probabilities over the
Arrowhead (>80%). There, probabilities for at least 8 inches of
snow are moderate (40-70%).


...CO Rockies/Sangre de Cristos...
Day 2...

Height falls at the southwest side of a large positively-tilted
longwave trough over the middle of North America will swing through
the central Rockies on Monday, brining with it a plume of residual
Pacific moisture. High pressure building in from the north in the
wake of a cold frontal passage Monday morning will result in some
weak upslope flow into Colorado's Front Range during the day. This
upslope component will extend as far south as the Sangre de Cristos
in northern New Mexico by Monday night. Periods of light-to-
moderate snow across the region are expected as the system moves
quickly through the region and heights build in by Tuesday. WPC
probabilities show >50% probabilities for at least 4 inches mainly
limited to the Sangre de Cristos in southern Colorado and northern
New Mexico, which does include the Raton Mesa. The highest and more
remote elevations could see localized amounts approach 8" by the
time the snow comes to an end Tuesday morning.

The probability of significant ice >0.25" across the CONUS is less
than 10 percent.

Fracasso/Mullinax


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