Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
256 PM EST Sun Dec 19 2021

Valid 00Z Mon Dec 20 2021 - 00Z Wed Dec 22 2021

...Unsettled weather lingers over the Pacific Northwest, the northern
Rockies and the Upper Midwest...

...Low pressure system in the Gulf of Mexico to deliver heavy showers and
thunderstorms to Florida and the Southeast coast...

...Dry and mild throughout much of the nation's midsection...

The week leading up to Christmas starts out active in the Northwest thanks
to a cut-off upper low in the northeast Pacific funneling moisture into
the region. A frontal system just off the coast will be responsible for
periods of coastal/valley rain and heavy mountain snow. A Flood Watch is
in place for parts of northwest Oregon through Monday morning, while
Winter Storm Warnings and Winter Weather Advisories stretching from the
Oregon/Washington Cascades to the High Plains of Montana are also in
effect into Monday morning. Snow totals through Monday are likely to
exceed a foot in parts of the Cascades and Bitterroots. A brief building
bubble of high pressure over southern British Columbia gives the Northwest
a break in the action during the day. The next push of Pacific moisture
arrives Tuesday evening into Wednesday with more lower elevation rain and
accumulating mountains snow, this time extending as far south as central
California. Meanwhile, a quick moving wave of low pressure in Montana will
produce light snow accumulations across the Northern Plains late Monday
into early Tuesday. This system then reaches the Upper Great Lakes by
Tuesday night where several inches of snow are possible.

To the south, an area of low pressure looks to form along a frontal
boundary in the Gulf of Mexico Monday morning. Spotty showers will track
along the immediate central Gulf Coast on Monday as the storm traverses
the central Gulf of Mexico. By early Tuesday morning the storm will have
strengthened and a threat for heavy rain and thunderstorms, some of which
could be severe, is expected across most of the Florida Peninsula. Some
thunderstorms could produce damaging wind gusts, tornadoes, and
waterspouts. Over an inch of rainfall is forecast across northern Florida,
southern Georgia, and far southern South Carolina through Tuesday evening.

Sandwiched between the active weather patterns in the Northwest and the
Southeast is upper level ridging that extends from the Great Basin to the
Mid-Atlantic coast. The result is high pressure dominating the pattern in
the central Rockies, the Nation's Heartland, and the Northeast. Mostly dry
conditions and abnormally mild temperatures for late December are forecast
in these regions the first half of the week, although chilly morning lows
are still likely in the Northeast Monday morning. In fact, mostly dry
conditions persists even as a more spring-like air-mass arrives late week
for most of the Plains and Mississippi Valley.

Mullinax


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