Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
257 PM EST Mon Dec 20 2021

Valid 00Z Tue Dec 21 2021 - 00Z Thu Dec 23 2021

...Developing area of low pressure in the Gulf of Mexico to deliver
locally heavy rain across northern Florida and the Southeast coast on
Tuesday before potentially spreading wintry precipitation into Maine on
Wednesday...

...Unsettled weather persists over the Pacific Northwest and Northern
Rockies into the middle of the week...

Wet weather is in the forecast throughout parts of the Sunshine State and
adjacent sections of the Southeast between tonight and Tuesday afternoon.
A low pressure system strengthening over the Gulf of Mexico is expected to
track northeast and over the northern Florida Peninsula on Tuesday. As it
does so, an attached warm front is expected to lift into the region and
fuel numerous showers and scattered thunderstorms. A few storms will have
the potential to produce heavy rain and instances of flash flooding,
particularly along Florida's central and northern Atlantic coastline.
Isolated severe weather is also a possibility throughout much of the
Florida Peninsula on Tuesday until a cold front clears southern sections
of the state by Tuesday evening. Showers will also spread into parts of
the Southeast and the eastern Carolinas through early Wednesday as the
aforementioned low pressure system passes by to the east. By Wednesday
afternoon, precipitation is expected to blossom to the north of the low as
an approaching upper-level shortwave interacts with the coastal system. As
a result, wintry weather may extend into parts of northern New England and
Maine on Wednesday. Mixed precipitation and freezing rain is possible
along coastal Maine, with the potential for heavy snow located just
inland. However, there remains rather large uncertainty regarding exactly
how far inland the impactful precipitation will reach.

Elsewhere, the aforementioned upper-level shortwave is currently found
across the Northwest and responsible for light-to-moderate snow extending
into the Northern Rockies tonight. This area of light snow will race
across the Northern Plains and into the Upper Midwest by Tuesday morning,
where a few inches of accumulating snow is possible. Parts of the Upper
Great Lakes will also enjoy some festive snowfall on Tuesday and Tuesday
night. For the immediate western U.S. coastline, continuous onshore flow
will allow for unsettled weather on Tuesday until the next system
approaches on Wednesday. Heavy snow is possible across the Cascade
Mountains and Sierra Nevada, as well as periods of moderate-to-heavy rain
along the northern California and Oregon coast.

For much of the central U.S., dry and mild weather is in store through
midweek as below average and bitterly cold temperatures remain confined to
the Northern Plains.

Snell


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