Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
319 PM EST Wed Dec 29 2021

Valid 00Z Thu Dec 30 2021 - 00Z Sat Jan 01 2022

...Bitterly cold wind chills in the northern Rockies and High Plains
through tomorrow, more heavy mountain snow from the Sierra Nevada to the
central Rockies...

...Record breaking Spring-like weather to stick around in the South before
spreading east; Enhanced Risk for severe storms and a Slight Risk for
Excessive Rainfall posted in parts of the Deep South today...

...Slight Risk for Excessive Rainfall in Southern California today and
Thursday; urban and flash flooding possible...

...Winter weather possible over the Plains/Midwest New Years Weekend...

The continental U.S. remains under the influence of prolonged troughing in
the Intermountain West and ridging in the Southeast. Beneath the troughing
pattern in the West, frigid temperatures are most common with dangerously
cold wind chills located in the Northern Plains. Wind Chill Warnings and
Advisories extend from Montana and parts of the Dakotas to northern
Minnesota where wind chills will range anywhere from -30 to -50 degrees.
Beginning late Thursday, a strong cold front will push the frigid airmass
southward toward the Central Plains, where overnight lows could dip below
zero by the weekend. In addition to the cold, accumulating snowfall
throughout the mountain ranges of the West are expected with heavy
accumulations for some. The heaviest snow totals today are forecast from
the southern Sierra Nevada and Transverse range of southern California to
the Wasatch and central Rockies. Snow totals in the highest peaks of these
regions will be measured in feet, which combined with whiteout conditions
in these areas will result in hazardous and, at times, impassable travel
conditions. The latest WPC Winter Storm Severity Index (WSSI) accordingly
depicts moderate to locally major potential winter storm impacts owing to
heavy snow accumulations over the Transverse Range and southern Nevada
today. Closer to southern California, a storm system rounding the base of
the upper trough in the West is funneling Pacific moisture into the Los
Angeles and San Diego metro areas. Excessive rainfall potential is high
enough to warrant a Slight Risk (threat level 2/5), meaning there is a
threat for flash flooding today and Thursday. Lastly, High Wind watches
were posted for southern Wyoming this Thursday as strong cross winds could
make for hazardous travel conditions for light weight and high profile
vehicles.

Farther east, the anchored ridge atop the southeastern U.S. shows no sign
in relinquishing its spring-like regime in the South and East-Central
U.S.. Numerous record warm lows and highs are anticipated from the
Southeast coast to the Rio Grande of South Texas today. More of the same
is expected in the Southeast on Thursday with highs in the 70s and lows
that are 20 to 40 degrees above normal. In time for the new year, the
unseasonable warmth is expected to spread into the Mid-Atlantic and
portions of the Northeast beginning Friday, where current forecast daytime
highs and warm minimum temperatures would threaten many records in the
region. A consequence of the warmth combined with windy conditions remains
an Elevated Risk (threat level 1/3) for fire weather for portions of the
southern High Plains today and tomorrow, per the Storm Prediction Center.
In terms of precipitation, moist southerly flow and increasing instability
levels will lead to an increasingly favorable environment for severe
weather. The Storm Prediction Center has issued an Enhanced Risk (threat
level 3/5) for parts of the Lower Mississippi Valley, while a Slight Risk
(threat level 2/5) stretches from Northeast Louisiana to eastward the
southern Appalachians, where tornadoes, damaging wind gusts, and isolated
large hail are possible today. Highly anomalous moisture content also
supports the threat for Excessive Rainfall, thus leading to the issuance
of a Slight Risk (threat level 2/5) for the Tennessee Valley today due to
a heightened chance for localized flash flooding. Scattered showers and
thunderstorms will remain possible across a broad portions of the South on
Thursday, but the severe and flash flood threat will be lower compared to
today's threat. A more focused threat of severe weather and heavy rainfall
returns to the Lower Tennessee Valley on Friday, with a Slight Risk in
effect for both hazards.  Meanwhile, a little farther north, light rain
and snow showers remain possible across the Lower Great Lakes Wednesday
evening. A dusting of 2 inches snowfall is possible from southern Iowa to
the northern Illinois and Indiana with a light but treacherous glaze of
ice possible from northeast Missouri to central Illinois and Indiana. A
more widespread threat of winter weather is possible over the Plains and
Midwest beginning this weekend as the aforementioned strong cold front
marches south from the Northern Plains. Accumulating snows and mixed
precipitation remain are possible along and north of the front as the
system arrives. However, uncertainty remains regarding specific
accumulations of snow and mixed precipitation. Check back for more details
as the event draws closer.

Asherman/Mullinax


Graphics are available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php