Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
341 AM EST Sat Jan 28 2023

Valid 12Z Sat Jan 28 2023 - 12Z Tue Jan 31 2023

...The West...
Days 1-3...

Expansive low anchored just north of Hudson Bay will dominate much
of North American continental weather through the middle of next
week with troughing and cold. Arctic-sourced air will continue to
plunge south over Rockies and Northwest from a digging shortwave
trough that is currently diving south over BC and will amplify
tonight along the OR Coast before traversing the CA coast through
Monday night with it closing into a mid-level low by the time it
reaches the Central CA coast Sunday night. This trough will
dislodge the stalled front currently along the Northern Rockies
yet this morning and send anomalous cold to the PacNW coast by
tonight and shift down the Inter-Mountain West and CA through
Monday. This now progressive system will limit additional snow in
MT to just a few inches after 12Z with Day 1 snow probabilities
for 6 or more inches moderately-high for most WY ranges and the
northern Wasatch across the ID/UT border as well as over the
Medicine Bow and Park Ranges into northern CO (where 1.5 to 3 ft
have already fallen) along with low to moderate probabilities for
the WA/OR Cascades and the Blue Mtns to the Salmon River.

As the primary trough axis retrogrades westward in response to the
amplifying shortwave along the CA coast Sunday, strong height
falls will drive the cold front farther southward while SW
mid-level flow provides a new surge of Pacific moisture downstream
of the closing mid-level low. This will limit heavy snow from the
southern OR and CA Cascades and instead focus on the
northern/central Sierra Nevada and over the eastern NV ranges
through the Wasatch in UT and again for northern CO where Day 2
snow probabilities are moderately high for 6 or more inches.

As the closed low deepens further and sinks to SoCal, the
intensifying upper diffluence and continued moisture confluence
over the Desert SW will allow heavy snow over the higher SoCal
Ranges, AZ north of the Mogollon Rim and across southern UT to
western CO ranges. The rapidly cooling airmass should support
above normal SLRs in this area as well, with fluffy/efficient
accumulation leading to moderately-high WPC probabilities for 6 or
more inches in these areas.


...North-Central Plains through the Midwest, Great Lakes and Well
Interior Northeast...
Days 1-2...

A leading shortwave trough over central Neb will continue to bring
locally heavy banded snow in frontogenetical (fgen) convergence to
its north this morning. However, as this impulse shifts eastward,
it will encounter slow height rises bulging across the Southeast
in response to more impressive height falls digging into the
Pacific Northwest. The resultant confluent upper flow into the
Ohio Valley will cause the vort max to shear off to the east,
causing an overall weakening trend in the shortwave amplitude and
associated forcing despite intensifying upper level jet energy
surging into New England during Sunday. Beneath this shortwave, a
wave of surface low pressure will move progressively along a
stationary front over the Midwest, but the fgen will ease as the
shortwave shears into the aforementioned confluent flow to the
east, with reductions to both the intensity and duration of
snowfall leading to lesser accumulations over the Midwest compared
to the north-central Plains. Day 1 snow probabilities are
moderately high for 4 or more inches after 12Z from the eastern
SD/Neb border across northern IA, southern WI and central MI.

Another north bump in the surface low track for Sunday keeps snow
along the Northeastern border with Canada with probabilities for 4
or more inches limited to the St. Lawrence Valley and far Northern
New England. Cyclonic flow over Lake Superior also brings moderate
probabilities for 4 or more inches to the western and eastern
sections of the U.P. of MI.


...North Texas through the Mid-South...
Day 3...

Cold air diving down the Plains will push over much of TX and the
Mid-South Sunday and be reinforced Monday into Tuesday. Pacific
moisture shifting across Mexico south of the low anchored off
SoCal will combine with Gulf moisture and allow southern Plains
precip to break out Monday which expands/shifts east through
midweek. A wintry mix of sleet and freezing rain is expected to
develop in this overrunning flow later Monday over North TX and
eastern OK and spread east over the Mid-South Monday night. As of
now a decent axis of freezing rain is forecast to form over
southeast OK, across northern AR and across the mid-lower Miss
Valley generally between Memphis and southern IL. Day 3 freezing
rain probabilities for over a tenth inch of ice are moderate
across these areas which will continue into Tuesday and raise the
prospect of a quarter inch of ice accretion, particularly over
north-central AR.


Jackson