Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
258 AM EST Mon Dec 13 2021

Valid 12Z Mon Dec 13 2021 - 12Z Wed Dec 15 2021

...There is a Moderate of excessive rainfall over parts of Central
California through Tuesday morning; There is a Slight Risk of excessive
rainfall over parts of Southern California on Tuesday into Wednesday
morning...

...Heavy snow over the Cascades, Sierra Nevada Mountains, and Northern
Rockies...

...Elevated Fire Weather risk for parts of the Southern High Plains...

Upper-level energy and a plume of moisture will impact the weather over
the West Coast, with a developing upper-level low beginning to move
onshore over the Pacific Northwest overnight Monday into Tuesday. A plume
of moisture will move southward along the California Coast to Southern
California and move into Mexico overnight Tuesday into Wednesday.

The moisture will produce coastal rain and higher elevation snow over the
Pacific Northwest and Northern/Central California and snow extending
eastward to the Northern Rockies through Tuesday.  The rain and snow will
expand into Southern California on Monday evening. The rain will be heavy.
Therefore, the WPC has issued a Moderate Risk of excessive rainfall over
parts of Central California through Tuesday morning. The heavy rain will
create numerous areas of flash flooding. Furthermore, many streams may
flood, potentially affecting larger rivers through Tuesday morning.

The heavy snow will be a long-duration event over the Cascades, Sierra
Nevada Mountains, and Northern Rockies. The snow will result in reduced
visibility and hazardous driving conditions. Furthermore, as the
upper-level low begins to move onshore, the snow levels will drop down to
sea level over parts of the Pacific Northwest and down to the surface over
parts of Northern California overnight Monday into Tuesday morning.

On Tuesday, the rain and higher elevation snow will end over pockets of
the Pacific Northwest and Northern California while continuing over
Central and Southern California.  Similarly, the rain will be heavy at
times over the Southern California Coast. Likewise, the WPC has issued a
Slight Risk of excessive rainfall over parts of Southern California from
Tuesday into Wednesday morning. Correspondingly, the associated heavy rain
will create mainly localized areas of flash flooding, with urban areas,
roads, and small streams the most vulnerable. Overnight Tuesday, as the
moisture moves into Northern Mexico, the rain and higher elevation snow
will wane over Southern California. However, the lower elevation rain and
snow will move into parts of the Southwest and deeper into the Great Basin.

High pressure over the Mid-Atlantic on Monday into Tuesday will usher in
warm temperatures over the Southern High Plains along with gusty wind. 
Therefore, the SPC has issued an Elevated Risk Fire Weather threat across
much of the Texas panhandle Monday into Tuesday due to warm temperatures,
low humidity, and increased wind (15-20mph). Along with the warmer
temperatures, moisture will start to stream northward over the Southern
Plains/Lower Mississippi Valley extending as far north as the Great Lakes
overnight Tuesday. As a result, showers and thunderstorms will develop
over parts of the Southern Plains and Lower Mississippi Valley by Tuesday.
In addition, overnight Tuesday, rain will begin to develop over parts of
the Great Lakes and Western Ohio Valley.

Ziegenfelder

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