Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
317 PM EST Tue Dec 28 2021

Valid 00Z Wed Dec 29 2021 - 00Z Fri Dec 31 2021

...Spring like temperatures persist in the South and East; elevated fire
weather risk for parts of the Southern Plains; bitterly cold wind chills
in the northern Rockies and High Plains today...

...Wintry weather to cause treacherous travel conditions from the Midwest
to the interior Northeast today; Slight Risks for severe storms and
Excessive Rainfall posted in parts of the Deep South Wednesday...

...Heavy snow for parts of the Sierra Nevada and Central/Southern
Rockies...

The jet stream pattern heading into the middle of the week indicates
persistent troughing over the western U.S., with a ridge established over
the Southeast. The result is a distinct separation of air-masses; winter
is in full control in the North and West while record-breaking spring-like
temperatures are firmly entrenched in the South and East-Central U.S.
South of the polar front, numerous daily record highs and warm lows are
expected throughout much of the South with daily temperature departures
ranging between 25 to 35 degrees above normal. The mixture of anomalous
heat, very dry conditions, and gusty winds keeps an Elevated Risk area for
fire weather conditions in place atop the southern High Plains through
Wednesday. The anomalous warmth is expected to linger over the South and
Mid-Atlantic through the new year, where additional daily high and warm
low records will be threatened through Saturday. To put the warmth in
perspective, lows that are warmer than the normal highs for late December
will be common from the Mid-Atlantic to the Gulf States through at least
Saturday. In the West, much colder temperatures are expected with the
coldest temperatures in the Northwest, northern Rockies, and northern High
Plains. Daily low temperatures will fall below -25 degrees in northern
parts of Montana and North Dakota, which combined with gusty winds cause
brutally cold wind chills through the end of the work week. Even daytime
highs will struggle to get above zero in these regions. Accordingly, a
Wind Chill Warning remains in effect along the northern Montana and North
Dakota border through Wednesday. The West Coast has the best chance to
witness record cold max temperatures through Wednesday, although
widespread record breaking cold is not anticipated.

As upper level disturbances track through the Intermountain West and head
east into the Plains, unsettled weather will become increasingly focused
in parts of the South and East. Light but still potentially hazardous
wintry weather is on tap from the Midwest and Great Lakes to the northern
Mid-Atlantic. Winter Weather Advisories have been posted not just for up
to a few inches of snow, but also an icy wintry mix of snow, sleet, and
freezing rain that could result in minor to locally moderate potential
winter storm impacts, per the WPC Winter Storm Severity Index (WSSI).
Within the storm's warm sector, periods of rain are expected from the
Middle Mississippi Valley to the Ohio Valley. Rain may fall heavily at
times and could lead to localized flash flooding, thus prompting the
issuance of a Marginal Risk for Excessive Rainfall. Farther south,
thunderstorms are in the forecast for the Lower Mississippi and Tennessee
Valleys with a Marginal Risk for severe storms in Southeast Louisiana and
Southwest Mississippi. As a new upper level disturbance ejects out of New
Mexico on Wednesday morning, it will support and even more favorable
environment for organized severe weather and excessive rainfall later in
the day on Wednesday. This has prompted the issuance of Slight Risks for
both severe weather and excessive rainfall tomorrow in the Tennessee
Valley and Deep South. Meanwhile, a lingering frontal system off the
Southern California Coast supports a threat of heavy rain through
tomorrow, where a Slight Risk was also raised for Wednesday. A Flood Watch
also remains over Southern California from Wednesday morning through
Thursday afternoon.

The ongoing troughing pattern out West will keep generating wintry weather
from the Sierra Nevada to the southern and central Rockies. The heaviest
snowfall accumulations will be confined to the Mogollon Rim of Arizona,
the Rockies of Colorado, and northern New Mexico. Snowfall totals in the
highest peaks will generally average 1 to 2 feet today with locally higher
amounts possible. Lighter accumulations compared to recent days are
anticipated today along the West Coast, but the next upper level feature
diving through the West Coast will usher in yet another round of heavy
snow to the Sierra Nevada late tonight into Wednesday. By early Thursday
morning, another 1 to 2 feet of snow will have fallen in throughout much
of the Sierra Nevada with locally higher totals in the tallest peaks.
Moreover, expect heavy snowfall chances to increase over the Cascades
toward Thursday, with moderate potential winter storm impacts highlighted
by the WPC WSSI. Expect more hazards travel conditions in these mountain
ranges through the middle of the week.

Asherman/Mullinax


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