Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
328 AM EST Wed Dec 15 2021

Valid 12Z Wed Dec 15 2021 - 12Z Fri Dec 17 2021

...There is a Moderate Risk of Severe thunderstorms over parts of the
Upper/Middle Mississippi Valley through Thursday morning...

...Heavy snow over the Sierra Nevada Mountains that will wind down on
Thursday; Chance of freezing rain over parts of the Upper Midwest and
Northern New England on Wednesday...

...Extreme Fire Weather risk for parts of the Central/Southern Plains;
Temperatures will be 25 to 40 degrees above average for the Plains,
Mississippi Valley, and Great Lakes/Ohio Valley...

A developing area of low pressure over the Central Plains will move
northeastward to the Upper Great Lakes by late Wednesday night, then move
into Central Ontario by Thursday.  The system will produce a myriad of
weather and associated hazards.  First, the storm will create snow from
the Northern Rockies to parts of the Southwest that will move onto the
Northern/Central Plains by Wednesday evening. Next, rain in the Great
Lakes will move into the Northeast, with light snow developing over parts
of Northern New England. Then, overnight Wednesday, as the warm air moves
in over the region, cold air will get trapped in the valleys and produce
areas of freezing rain over parts of Northern New England through Thursday
evening. Additionally, isolated pockets of freezing rain will develop over
parts of the Upper Midwest along the rain-snow line on Wednesday afternoon
into the late evening.

Third, the rain over the Upper Great Lakes will begin to become more
convective in nature (thunderstorms). During the afternoon, showers and
thunderstorms will develop along and ahead of the associated front; some
of the thunderstorms will become severe.  Therefore, the SPC has issued
Moderate Risk of Severe thunderstorms over parts of the Upper/Middle
Mississippi Valley through Thursday morning.  The hazards associated with
these thunderstorms are frequent lightning, severe thunderstorm wind
gusts, hail, and a few tornadoes. There is a 10% or greater probability of
65 knots or greater wind gusts over the region.  The thunderstorms will
wind down over the Upper Midwest and change over to snow by Thursday.

The fourth hazard will be high wind associated with the strong pressure
gradient associated with the deep area of low pressure. Therefore, high
Wind Warnings are posted from the Central/Southern High Plains to the
Great Lakes, with Storm Warnings over Lake Michigan.

Furthermore, ahead of the front, temperatures will be 25 to 40 degrees
above average for the Plains, Mississippi Valley, and Great Lakes/Ohio
Valley. In addition, many record-high temperatures are forecast over parts
of the Southern Plains into the Upper Midwest. Along with the heat, the
SPC has issued an Extreme Fire Weather risk for parts of the
Central/Southern Plains through Thursday morning. Very dangerous
wildfire-spread conditions will be over the region, with dry fuels and
very windy conditions with wind gusts up to 40+ mph.

Moreover, the showers and thunderstorms will continue along the front over
the Lower Mississippi Valley into the Southern Plains. Moisture from the
Gulf of Mexico will pool along the front producing heavy rain. Therefore,
the WPC has issued a Marginal Risk of excessive rainfall over parts of the
Ohio, Tennessee, and Lower Mississippi Valleys on Thursday into Friday
morning.  The associated heavy rain will create localized areas of flash
flooding, affecting areas that experience rapid runoff with heavy rain.

In the meantime, a front will move onshore over the Northwest that will
move southward over the West Coast and dissipate by Thursday evening, as
the associated upper-level energy moves inland to the Rockies by Friday.  
The system will produce coastal rain and higher elevation snow over the
Pacific Northwest and Northern California. The rain and snow expand into
Central California and the Great Basin overnight Wednesday.  Rain will
move into parts of Southern California on Thursday.  The rain and snow
start to wind down overnight Thursday over the Pacific Northwest and
California. Concurrently, snow will move into parts of the
Northern/Central Rockies and the Northern High plains by Friday morning.

Ziegenfelder


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