Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
353 PM EST Sun Jan 22 2023

Valid 00Z Mon Jan 23 2023 - 00Z Thu Jan 26 2023

...Northeast...
Day 1...
As a highly-amplified upper trough moves east of the Mississippi
Valley this evening, low pressure is forecast to develop along the
Mid Atlantic coast and strengthen as it moves to the Northeast
coast overnight.  Generally light to moderate snow associated with
a low-to-mid level front is forecast to move east from the Great
Lakes into the Northeast this evening, before moderate to heavy
snow begins to develop in the deformation zone on the north side
of the low tonight.  In addition to the favorable upper forcing,
low-to-mid level frontogenesis is expected contribute to the
development of moderate to heavy banded snow from the Catskills
and the upper Hudson Valley eastward through western
Massachusetts, southern Vermont and New Hampshire, and coastal
Maine.  The 12Z HREF guidance indicates rates of 1-2 in/hr are
likely across this area.  WPC probabilistic guidance shows that
accumulations of 6 inches or more are likely, with amounts of a
foot or more possible along this axis. 

...Southwest to the southern Rockies...
Day 1...
An anomalously deep upper low will continue to develop and drop
south through the Great Basin into the Southwest tonight.  By
early tomorrow, the consensus of the 12Z guidance shows a 540 dm
low (minus 3 sigma) at 500 mb centered over southern Arizona. 
While widespread heavy snows are not expected, this has the
potential to produce some low amount/high impact snows across the
lower elevations of southern Arizona.  Locally heavy accumulations
are possible across the higher elevations, including the Grand
Canyon region, Mogollon Rim and the White Mountains in Arizona. 
Locally heavier amounts are also expected farther east across the
San Juan Mountains of southwestern Colorado.  WPC guidance
indicates amounts of 4 inches or more likely across the higher
elevations, with amounts up to 8 inches possible on the highest
peaks.  

...Southern Rockies and southern Plains...
Day 2...
The previously noted low is forecast to swing east and move along
the U.S.-Mexico border into West Texas late Monday into early
Tuesday.  This will bring measurable snow across much of central
and southern Mexico, with high elevation heavy snow possible.  The
greatest threat for heavy amounts is expected to focus along and
east of the Sacramento Mountains.  Left-exit region upper jet
forcing, along with increasing low level easterly flow on the
north side of the developing low are expected to enhance the
potential for locally heavy amounts in the favored terrain.

On Tuesday, the upper low is forecast to transition to an open
wave and begin to take a negative-tilt as it moves from West Texas
to North Texas and southeastern Oklahoma.  Left-exit region upper
jet forcing is forecast to translate east into the Texas
Panhandle- Rolling Plains region, supporting a swath of at least a
few inches across the area on Tuesday.  Probabilities for
accumulations of 4 inches or more have increased with the latest
run across this area.  Probabilities for at least measurable snow
have also increased farther east from the Texas Panhandle eastward
across southern Oklahoma.

...Ozarks to the central Appalachians, Mid Atlantic, and
Northeast...
Days 2-3...
The upper trough swinging across the southern Plains will continue
to take a negative-tilt, supporting the intensification of a
surface low as it tracks northeast from eastern Texas through the
lower Mississippi Valley into the Mid South Tuesday night.  There
is a growing signal for banded moderate to heavy snow developing
on the northwest side of the low.  Here also, favorable upper
forcing in concert with low-to-mid level frontogenesis are
expected to contribute to the potential for mesoscale banding and
heavy rates beginning across eastern Oklahoma and the Ozarks
starting Tuesday night, before lifting northeast across southern
Missouri into the lower Ohio Valley.  WPC probabilities indicate
that accumulations of 4 inches or more likely from the Ozarks
across southern Missouri, with amounts of 8 inches or more
possible, especially in the higher elevations of the Ozarks.

On Wednesday, the system is forecast to track progressively to the
northeast into the Great Lakes, supporting a stripe of at least a
few inches of snow from southern Illinois to southern Michigan. 
Within this stripe, mesocale banding is likely to contribute to
areas of heavier totals.  Latest WPC guidance indicates a greater
threat for higher amounts centered across central to northeastern
Indiana Wednesday morning.

In the warm advection pattern ahead of the system.  High pressure
centered over eastern Canada will support precipitation beginning
as a wintry mix or snow across the central Appalachians, interior
Mid Atlantic, and the Northeast before transitioning to rain
across most areas.  WPC probabilities indicate precipitation will
remain snow long enough to produce accumulations of 4 inches or
more across northern portions of the Allegheny Mountains into
central Pennsylvania.

Pereira