Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
250 PM EDT Tue Nov 01 2022

Valid 00Z Wed Nov 02 2022 - 00Z Sat Nov 05 2022

...Western U.S....
Days 1-3...

Longwave troughing along the Western U.S. today sharpens and digs
as it shifts eastward over the next 12-24 hours and eventually
digs well into the Southwest U.S./Four Corners region by the end
of the period (Friday). For Day 1, a lead shortwave trough will
move from northern California into Idaho and western Montana
through Wednesday. The combination of strong upper divergence,
frontogenesis at the nose of the modest PW plume and upslope
enhancement will help drive moderate to locally heavy snow for the
higher elevations, generally above 6000 ft, across the Sierra,
Oregon Cascades, central to northern Idaho ranges, and Uintas in
Utah. Rates may likely exceed 1"/hr in northern areas but perhaps
2"/hr over the central Sierra above 7000ft. Snow levels will drop
in the wake of the cold front, with some light snow possible down
to about 3500ft. This shortwave will also enhance snowfall over
northern ID and northwestern MT tonight into early Wednesday where
WPC probabilities for at least 8 inches are above 50%, including
the Oregon Cascades and Blue Mountains.

For Day 2, a stronger digging shortwave will round the base of the
longwave trough, reaching well south into southern California and
the Four Corners region by Thursday. The strong baroclinic zone
transitions to Great Basin and central Rockies along with lowering
snow levels. This supports the heaviest snowfall over the Wasatch,
southern Utah ranges, Unitas, and the Colorado San Juans. WPC
probabilities are high for at least 4 inches in these areas and
show a strong signal for 8"+ over the highest terrain. Further
north, the Wyoming ranges will likely pick up several inches
between the better forcing but enhanced via upslope into the Wind
River Range and Bighorn Mountains.

Moderate to locally heavy snow will remain possible early on Day 3
over the central Rockies as the mid/upper level shortwave trough
moves overhead. By the end of the period, the better forcing and
moisture will move into the Plains but lingering light snow will
remain possible. The greatest probabilities for accumulations
greater than 4" look to be across northern New Mexico ranges. Back
to the Pacific Northwest, the next strong atmospheric river will
approach late in the period. Initially, snow levels look to be low
enough for moderate to locally heavy snowfall over WA Olympics and
Cascades but the impressive moisture plume and warm air advection
will raise snow levels to 7000-8000ft+ during the period should
keep any other significant snowfall to the highest peaks of the WA
Cascades and northern Idaho.


The probability of significant icing greater than 0.25" is less
than 10 percent.

Fracasso/Taylor