Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
244 PM EST Thu Dec 16 2021

Valid 00Z Fri Dec 17 2021 - 00Z Sun Dec 19 2021

...Quasi-stationary boundary to produce heavy rain and potentially severe
thunderstorms from the Southern Plains to the Ohio Valley through Saturday
morning ...

...Moderate to heavy snow and freezing rain to impact interior New England
on Saturday...

...Elevated Fire Weather Risk for the Southern High Plains into the
weekend...

...Temperatures expected to remain well above average from the Southern
Plains to the Northeast...

The deep low pressure system at the center of yesterday's historic weather
has since exited the CONUS and is presently located over central Ontario,
Canada. Though no longer stateside, high winds on the backside of this
system, with gusts up to 60 mph, can still be felt over and around the
Great Lakes. As such, High Wind Warnings are currently in effect over
portions of Michigan, Storm Warnings are in effect from Lake Superior to
Lake Huron, and Wind Advisories have been put into effect over the Upper
and Lower Great Lakes through tomorrow morning. As the system progresses
to the northeast overnight light snow is expected to linger over the Upper
Midwest. In the meantime, showers and thunderstorms will form along a
strong cold front draping from the Northeast to the Southern Plains. Ample
atmospheric moisture will allow for 1-3 inches of rain to fall over the
Lower Mississippi and Tennessee Valleys where already saturated soils will
heighten the risk of flash floods, prompting the issuance of a Marginal
Risk of Excessive Rainfall by the Weather Prediction Center through Friday
morning. In addition to the flood risk ample instability over the Lower
Mississippi Valley will support the development of severe thunderstorms
that may produce damaging winds and large hail, therefore, the Storm
Prediction Center has issued a Marginal Risk of Severe Thunderstorms for
the region through Friday morning.

The aforementioned cold front is forecast to become a quasi-stationary
boundary overnight, settling primarily over a region extending from the
Southern Plains to the Ohio Valley. With the boundary remaining virtually
motionless over a 24 hour period, any associated heavy rain will fall over
the same area, saturating the already wet soils with an additional 1-3
inches of rain and heightening the risk for flash flooding. To account for
this the Weather Prediction Center has issued a Slight Risk of Excessive
Rainfall from northeast Texas to the western Ohio Valley effective Friday
morning to Saturday morning. On the western periphery of this Slight Risk
area lies a concurrent area highlighting a Marginal Risk for Severe
Thunderstorms issued by the Storm Prediction Center given the chance that
damaging winds and hail develop in thunderstorms that form over the
region. By Saturday the risk of flash flooding and severe thunderstorm
development will diminish as high pressure building over the Great Plains
quickly ushers the front to the Gulf Coast and Eastern Seaboard. As the
front is pushed ahead a new low pressure wave will develop and lift to the
north, reaching the Ohio Valley and Mid-Atlantic by Saturday evening. To
the north of this wave light snow is forecast to fall over the Upper
Midwest, while more moderate snowfall is expected over the interior
Northeast. As warm air is pulled north by a warm front extending to the
east of the low pressure system the snow is expected to quickly change
over to freezing rain, leaving behind a thin layer of ice extending east
from Lake Erie to central Massachusetts that will make road conditions
hazardous.

In the Southern High Plains modestly dry and breezy conditions are
forecast to persist over extremely dry fuels through Friday morning, while
similar conditions are expected to arise Friday morning to Saturday
morning over the Central High Plains. Given the fact these conditions are
conducive to fire spread, the Storm Prediction Center has issued an
Elevated Risk of Fire Weather for the Southern High Plains through
tomorrow morning and the Central High Plains Friday morning through
Saturday morning.

Elsewhere, a stationary boundary meandering through the Northern and
Central Rockies will support heavy snowfall over the regions' high
elevation mountain ranges through Friday morning. The eastward progression
of shortwave instability at the surface will guide this snowfall out of
the mountains and into the Northern Plains on Friday where light to
moderate accumulations are expected. In the Pacific Northwest, a system
moving onshore Saturday is forecast to bring rainfall to the coast and low
elevation areas, while heavy snow is expected over Olympics and northern
Washington Cascades before spreading east into the Northern Rockies
Saturday evening.

Temperature-wise, unseasonably warm record-breaking weather is forecast to
persist from the Southern Plains to the Northeast into the weekend. With
today's daily highs sitting 20 to 30 degrees above normal, 56 daily high
temperature records throughout the eastern half of the country have
already fallen. A handful of tomorrow and Saturday's daily high
temperature records will also be put to the test as highs are forecast to
reach a modest 10 to 20 degrees above normal. In stark contrast to the
east, temperatures out west have dropped moderately to 5 to 10 degrees
below normal. An even larger departure from normal is expected over the
Northern High Plains, where daily highs could drop to as low as 20 degrees
below normal on Friday.


Zavadoff


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