Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
231 AM EST Tue Jan 30 2024

Valid 12Z Tue Jan 30 2024 - 12Z Fri Feb 02 2024

...Southern and Central Appalachians...
Day 1...

Clipper system over the Great Lakes this morning will continue to
dive southeastward today, spreading light rain/snow across the
Midwest and eventually into the central/southern Appalachians
after dark. Quick movement and modest moisture will limit amounts,
but upslope into the higher terrain could squeeze out a few inches
of snow over eastern WV and along the TN/NC border.


...California into the Great Basin/Four Corners...
Days 2-3...

A strong, extended Pacific jet will aim toward coastal CA midweek
before splitting N-S along the coast, with a deep upper low to the
north and strong upper ridging in the sub-tropics. At the surface,
a wound-up area of low pressure (low 960s mb) will head toward
British Columbia as its cold front reaches the US Coast around
Wednesday morning. Thereafter, the mid-level trough will split
into two pieces, with generally lighter QPF to the north (WA/OR)
as the main moisture plume (PW anomalies +2 to +3 sigma) separates
as well. Over CA, nose of the Atmospheric River oriented
south-to-north late Wednesday into NorCal will then pick up a bit
more speed as it shifts orientation to SW-to-NE as the height
falls continue eastward into the Great Basin. By the end of D3
(12Z Fri), jet will extend into northern Mexico with broad lift
continuing on its poleward side over the Southwest/Four Corners
and precipitation spreading as far east as about as the Rockies.
Temperatures will fall behind the front, lowering snow levels from
rather high levels initially (~6000-7000ft) given the warm
antecedent conditions down to as low as about 4000ft over NorCal
by early Fri as precipitation becomes much lighter. Snow will
become increasingly impactful to many passes over NorCal and
especially across the Sierra on Wednesday afternoon into Thursday,
expanding eastward across the Great Basin Thursday and into the
Four Corners Thursday evening and continuing beyond the end of
this forecast period (12Z Fri).

Heavy snowfall and intense snowfall rates of 2-4"/hr are likely in
the highest elevations of the Shasta/Siskiyou/Trinity ranges then
into the Sierra, where multiple feet of snow is likely through
this forecast period above 8000ft or so. A much broader area of
lighter but modest amounts of 4 inches is forecast for parts of
central ID (tied to the northern portion of the expansive trough),
central NV, southern UT, northern AZ along the Mogollon Rim, and
into the San Juans in southwestern CO. Snowfall amounts east of
the Sierra will be highest above 8000ft or so, aided by upslope
flow (especially NW-SE oriented ranges).


...Northern Maine...
Day 3...

Canadian cold front will sweep eastward across southern Quebec and
across the Northeast Thursday into early Friday, spreading snow
across northern New England transitioning to rain toward the
Mid-Atlantic. Trend has been for a bit more QPF over the area over
the past few model/ensemble runs, maximized over northern Maine.
There, WPC probabilities for at least 4 inches of snow are about
30-40%.


The probability of significant icing greater than 0.10" is less
than 10% for days 1-3.


Fracasso