FOUS11 KWBC 260835
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 AM EST Tue Nov 26 2024

Valid 12Z Tue Nov 26 2024 - 12Z Fri Nov 29 2024

...Upper Great Lakes and Interior Northeast...=20
Days 1 and 3...

A negatively tilted trough over the Great Lakes will lift over New
England today. Warm air advection ahead of the surface triple point
that tracks east over southern NY this morning will continue to
cause freezing rain to fall in sheltered valleys mainly around the
White Mtns after 12Z where Day 1 PWPF for >0.1" ice is around 20%.
Otherwise cyclonic flow over the Lakes behind the system will
continue to allow LES off WNWly flow to spread over northern MI=20
and the Tug Hill east of Lake Ontario where Day 1 PWPF for >4" snow
is 10-50% in preferred snow belts with upwards of 6" in the
Superior coastal sections of the eastern U.P.=20

A reinforcing northern stream trough amplifies as it crosses the=20
Midwest Wednesday night, taking on a negative tilt as it lifts over
New England Thursday, promoting rapid surface cyclogenesis over=20
the northern Mid-Atlantic and New England coasts through Thursday=20
night. Arctic-sourced air shifting in with this trough will=20
reinvigorate LES of Lakes Superior and Michigan where Day 3 PWPF=20
for >4" are 20-60% over typical U.P. and northern L.P. snow belts=20
in WNWly flow.=20

Deformational snow banding is expected to develop late Wednesday
over/just south of the eastern Great Lakes and intensify late
Wednesday night through Thursday in a narrow corridor of the
interior Northeast north and behind the rapidly developing coastal
low. Day 3 PWPF for >4" are rather focused on terrain with 30-60%
probs over the Tug Hill, Adirondacks, Greens, Whites, and far
northern Maine. However, given the expectation for banding, heavy
snow is likely in at least a narrow swath northeast from far NWrn
PA through interior New England regardless of elevation. Details on
the location and intensity of this band will further increase as it
enters the finer resolution model timeframes. Those with Interior
Northeast interests over Thanksgiving should closely monitor this
snow forecast as it should be a disruptive event across portions=20
of the interior Northeast from Thanksgiving into Friday. The
Arctic-sourced cold and subsequent LES off the Great Lakes through
the weekend is the subject of the Key Messages which are linked
below.=20


...Southern Sierra Nevada, central Nevada and Utah ranges...=20
Day 1...

An atmospheric river will continue to deliver a relatively narrow
axis of rich Pacific moisture over the southern Sierra Nevada east
through the southern Wasatch through this evening above snow levels
around 8500ft. The 00Z HREF continues to indicate particularly=20
heavy 2-3" snowfall rates will occur today on the highest southern=20
Sierra Nevada and more like 1-2" for the central Nevada and=20
central/southern Utah ranges into this evening. Snow levels drop=20
to 5000ft overnight as the rates drop off after a positively-tilted
northern stream trough axis passes. Day 1 PWPF for >12" are=20
categorical over the highest central Utah terrain and 1-3'=20
additional is expected over the highest southern Sierra Nevada.=20

This should result in significant disruption to those in such high
elevations with tree damage and power outages possible.


...CO Rockies...=20
Days 1-2...

The atmospheric river responsible for the copious amounts of heavy
snowfall over the Sierra Nevada will direct highly anomalous=20
Pacific moisture into the southern Rockies into Wednesday. Strong=20
upslope ascent in the southern CO ranges will be coupled with=20
potent right entrance region jet dynamics results in heavy=20
snowfall above 7000ft in northern CO and 8500ft in southern CO=20
today with levels dropping to around 5000ft late tonight in the
north and 6000ft Wednesday morning in the south as rates taper=20
off. Prolonged rates of 1-2" per hour are forecast by the 00Z HREF=20
today and tonight over most western slopes of the CO Rockies with
maxima in ranges such as the San Juans and Sawatch where Day 1 PWPF
for >12" are categorical. The WSSI shows swaths of Moderate to=20
Major Impacts for most CO ranges. Widespread closures and=20
disruptions to infrastructure are also anticipated in areas=20
expecting Major Impacts.=20

Moderate snow is likely along eastern CO slopes and the Palmer
Divide Wednesday as lee-side cyclogenesis occurs over southeast CO
before dipping into the TX Panhandle. Day 2 PWPF for >4" is
generally 20-50% immediately east of the southern Front=20
Range and Sangre de Cristos including the I-25 corridor.=20


Jackson



...Winter Storm Key Messages are in effect for the northern Plains
and Great Lakes...=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late=
stKeyMessage_1.png__;!!DZ3fjg!5PFGUr-MONZQnsk-OBQXtFxnBIqdRROZQh2QFNpjjCY8q=
ZTYJN3NNIc67bTf5DV1zLDXUBZdfOjjX426uuUVxBs3Ifs$=20

$$

=3D =3D =3D
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