279
FOUS11 KWBC 231844
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
144 PM EST Sat Nov 23 2024

Valid 00Z Sun Nov 24 2024 - 00Z Wed Nov 27 2024

...Intermountain West and Rockies...
Day 1

A developing low in western Montana will form on shortwave energy
rounding the base of an amorphous longwave trough over the Pacific
Northwest and western Canada. Residual atmospheric moisture will be
in place from last week`s atmospheric river event. Thus, expect
areas of heavy snow over many of Idaho, western Montana, and
western Wyoming`s mountains through Sunday. The heaviest rates will
be largely concentrated in the mountains due to locally forced
upslope flow. However, as snow levels crash below 4,000 ft, higher
valleys will also pick up some light snowfall accumulations.
PWPF values into Glacier N.P. and the Sawtooths of Idaho are over
90% at the highest elevations for 8 inches or more of snow. For
Yellowstone and Grand Teton N.P.s the values are over 60%.

The low will quickly propagate to the Plains as leeside troughing
and some weakening of the upper level jet bring the largest
pressure falls into southeast Montana/northeast Wyoming by Sunday
afternoon. This will quickly end the heavy snow over the
aforementioned mountains, perhaps as early as Sunday morning. With
diminishing atmospheric moisture further east, this will end the
significant snowfall threat by Sunday evening.

...Upper Great Lakes...
Day 2-3

On Sunday night, energy from two separate disturbances...one an
upper level low over the Canadian prairies, and the other an
ejecting shortwave out of California/Nevada...will merge over a
strong cold front over the northern Plains. The combination of all
of that upper level energy and the surface front will result in
cyclogenesis near Lake Michigan on Monday morning. The low will
allow for heavy snow to develop to the north near Lake Superior,
especially the U.P. As the low tracks northeast across the L.P.,
much colder air wrapping around the back side of the low will allow
for widespread lake-effect snow and snow showers persisting into
Tuesday for much of the U.P. Expect a widespread 3-6 inches of snow
over much of the Lake Superior shoreline from the Arrowhead through
the U.P.

Wegman


...Northern New England...
Days 1-2...

Upper low moving northward over Atlantic Canada will continue
northward as additional height falls cross through the eastern
Great Lakes into New England overnight, promoting an area of snow
over far interior Maine into northern NH/VT. WPC probabilities of
an additional 4 inches of snow are moderate (>40%) over these
areas, mainly in the higher terrain above 2000ft or so. Light snow
is also favored over eastern NY (Adirondacks into the Catskills)
but amounts should be under 4 inches.

...Sierra, Wasatch, CO Rockies...
Days 1-3...

Troughing off the West Coast will continue into next week, with a
rather steady stream of moisture into the region. Generally lighter
snow is forecast for D1 above 6000ft or so (Sierra) with any
moderate accumulations (>6") limited to above 7000ft where WPC
probabilities are >40%. By D2, another surge of moisture will aim
toward the Sierra as PW and IVT values climb above the 95th
percentile per the NAEFS ESAT. With a favorable WSW flow into the
central/southern Sierra, moderate to very heavy snow is likely for
areas south of Lake Tahoe into D3 as PW/IVT anomalies peak above
the 99th percentile. Snow levels will rise well above 7000ft to
9000ft (north to south) but those high elevations may see several
feet of snow over the two-day period. WPC probabilities for at
least 24 inches of snow are highest above 8000ft with the highest
peaks possibly receiving closer to four feet.

Farther east, 120-140kt upper jet will stream across the Great
Basin with the axis of moisture focused across southern NV/UT. This
will set up westerly flow into the Wasatch and then the CO Rockies with
moderate snow accumlations D3 as snow levels will be high
(7500-9000ft). WPC probabilities for at least 8 inches are >50%
above 10,000ft in the Rockies.

Fracasso


$$