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

Valid 12Z Sun Jan 22 2023 - 12Z Wed Jan 25 2023

...Northeast...
Days 1-2...

A deep upper trough traversing the Mississippi Valley on Sunday
spawning a wave of low pressure in the Southeast will track up the
Southeast coast Sunday night and off the New England coast by
Monday morning. Ahead of the upper trough, unusually rich moisture
for late January races up the Eastern seaboard Sunday night. At
the same time, a sufficiently cold air-mass will reside over the
interior Northeast. There is a slight chance (10-20% chance) for
freezing rain accumulations >0.1" in parts of the central
Appalachians of WV/VA and the Catskills. There is a rather large
swath of 40-60% probabilities for at least a very light coating of
freezing rain from the Blue Ridge and Laurel Highlands to the
Poconos today as well. Temperatures will not be sub-freezing along
the I-95 corridor to result in periods of snow Sunday evening, but
their more inland and elevated neighbors to the north and west
have much better odds of receiving heavy snow, especially from the
southern tier of NY on north and east into central ME. Strong
vertical ascent beneath the right-entrance region of a jet streak
lifting north over ME and southeast Canada, combined with
anomalous moisture content (PWs >90th climatological percentile
according to NAEFS at 06Z Mon), will account for heavy periods of
snow from the Catskills and Adirondacks on east to the Berkshires,
southern VT and NH, and just north of the ME coastline Sunday
night into Monday morning. After the initial front end thump via
850-700mb WAA Sunday night, the 850mb low forming over the
southern New England coast early Monday morning directs low-level
moisture flux within easterly flow back into southern New England.
This conveyor belt of Atlantic moisture will lead to a brief
deformation axis of snow that could result in a couple inches of
snow across southern New England on Monday morning. Latest WPC
PWPF shows 40-60% probabilities for >8" of snow in the Catskills,
northwest MA, and portions of the Green and White Mountains of VT
and NH. There are also some 50-70% probabilities for >4" of
snowfall in the central Appalachians of WV where strong upslope
enhancement is likely to result in periods of heavy snow there
Monday morning.

...Southern Rockies, Southern Plains, & Ozarks...
Days 2-3...

An upper low tracking across southern Arizona will foster a
favorable environment for a strengthening storm system tracking
into central Texas by Tuesday morning. By Monday night, a
strengthening 250mb jet streak over northern Mexico and the Davis
Mountains place its diffluent left-exit region over eastern New
Mexico and the TX Panhandle. In response to the falling heights
and pressures over northern Mexico and southern New Mexico, the
LLJ will strengthen to 50 knots and usher in rich 850mb moisture
flux up the Rio Grande Valley and into the southern High Plains.
This is quite impressive for late January, registering above the
99th climatological percentile according to NAEFS at between
06-12Z Tuesday. This should result in a classic warm conveyor belt
of moisture to the north and west flanks of the 700mb low,
allowing for the formation of a TROWAL that will produce periods
of heavy snow. There does remains some uncertainty on the track
and intensity of the deformation axis. It does appear
thermodynamic profiles beneath the TROWAL are sufficiently cold
enough to produce snow, but guidance is not yet in agreement on
the level of FGEN forcing, positioning, and timing. Still, this
event has the potential to be the most impactful winter storm of
the season for portions of the TX Panhandle and into parts of
southern OK and northern TX. Latest PWSSI does depict 40%
probabilities for Moderate impacts between Amarillo and Lubbock
through Tuesday morning, with the highest probabilities (40-60%)
focused in the Sacramento Range of New Mexico. It is worth noting
the 12Z ECMWF EFI did have a rather extensive shift of tails area
that stretched from southern NM and northern TX to western AR
between 00Z Tues - 00Z Wed. What this speaks to are some of the
ensembles outcomes for potentially significant snowfall totals
with respect to climatology, while at the same time showing there
remain a wide range of potential outcomes for all areas in
between. Continue to monitor the forecast closely over the next
couple days as subtle adjustments in frontogenetical forcing could
cause additional changes to the snowfall forecast (for less
amounts or higher) over the next 24-36 hours.

As the surface low organizes in southeast TX around midday
Tuesday, the deformation axis is forecast to reorganize as it
tracks over the Red River with periods of snow possible from
Wichita Falls to the OKC metro area Tuesday morning. The
impressive LLJ mentioned above looks to continue across southeast
TX and eventually into southern LA. This LLJ will provide a large
quantity of Gulf moisture into the Ozarks and Central Plains.
NAEFS showed an expansive area of 500-700mb mean specific humidity
values >90th climatological percentile, allowing for highly
saturated DGZs residing within the 500-600mb layer on average. In
addition, the nose of this 70-80 knot 850mb jet will be aimed at
the Ozarks, allowing for strong vertical ascent via upsloping flow
into the Ozarks on top of the robust synoptic-scale ascent from
the negative 250-500mb trough pivoting over the Southern Plains.
This setup makes the Ozarks the highest confidence area for heavy
snow as of this forecast update. Latest WPC PWPF shows 40-60%
probabilities for >6" of snow in northwest Arkansas on Tuesday, as
well as a 60% chance for Moderate impacts according to the
experimental PWSSI. There are ecen some 10-30% probabilities for
>6" of snow in the Ouachita mountains of eastern OK and western
AR. Eventually, this storm system will provide periods of snow to
the Lower Great Lakes where locally heavy snowfall totals are
possible.

...Intermountain West...
Day 1 & Day 3...

The upper trough that becomes responsible for the Southern Plains
and Rockies winter storm Monday into Tuesday originally will bring
periods of mountain snow to many of the mountain ranges of the
Intermountain West today. A passing cold front leads to a
northerly, upslope flow into central MT and northern WY today.
Most snowfall amounts will be short of approaching warning
criteria, but there are still some opportunities for >4" of
snowfall in ranges such as the Blue of northeast OR, the Wasatch,
the Wind River, and the mountain ranges of central MT. The two
ranges with the best chances (>60%) for snowfall >4" is the
Mogollon Rim of northern AZ and the San Juan of southwest Colorado
tonight and into Monday. The region gets a reprieve on Monday
(albeit some light snowfall may still linger for some areas in the
central Rockies) before the next upper level disturbance dives
southeast from western Canada Monday night. This will help to
produce a burst of snow across the Northern Rockies on south to
the Colorado Rockies. The mountain regions with the best odds of
receiving >4" of snow are the Absaroka and Big Horns where
probabilities according to WPC PWPF are as high has 60% in the
tallest peaks. Locally hazardous driving conditions are possible
today and Tuesday in these effect mountain ranges.

Mullinax