Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
222 AM EST Thu Dec 21 2023

Valid 12Z Thu Dec 21 2023 - 12Z Sat Dec 23 2023

...There is a Moderate Risk of excessive rainfall over parts of Southern
California on Thursday...

... There is a Slight Risk of excessive rainfall over parts of Southern
California and the Southwest on Friday...

...Light to moderate snow over the Cascades/Northern Intermountain
Region/Central Rockies and snow at the higher elevations over parts of the
Southwest, Great Basin, and Southern Rockies on Friday...

An upper-level off the Southern California Coast will slowly move
southward over the Pacific before moving inland over the Southwest and
Northwestern Mexico by Saturday. The low will stream moisture into
Southern California, creating heavy rain. Therefore, the WPC has issued a
Moderate Risk of excessive rainfall over parts of Southern California
through Friday morning. The associated heavy rain will create numerous
areas of flash flooding with narrow canyons/gullies and burn scars the
most vulnerable. Furthermore, many streams may flood, potentially
affecting larger rivers. In addition, thunderstorms will develop closer to
the southern border.

On Friday, as the upper-level low begins to move onshore, heavy rain will
start to move into the Southwest while continuing over parts of Southern
California. Therefore, the WPC has issued a Slight Risk of excessive
rainfall over parts of Southern California and the Southwest from Friday
into Saturday morning. The associated heavy rain will create mainly
localized areas of flash flooding, with urban areas, roads, small streams,
narrow canyons/gullies, and burn scars the most vulnerable.

Meanwhile, a front over the Eastern Pacific moves onshore over the Pacific
Northwest on Friday and then to the Northern High Plains by Saturday. The
system will produce rain and higher-elevation snow over parts of the
Northwest. Overnight Friday into Saturday, snow will develop over parts of
the Northern Intermountain Region. Moreover, overnight Friday, snow will
develop over parts of the higher elevations of the Southwest and
Central/Southern Rockies.

Furthermore, the circulation around the area of high pressure over the
Southeast/Mid-Atlantic will produce return flow off the Gulf of Mexico
that will slowly moisten the air over the Central/Southern Plains
northward to the Great Lakes. Light rain will develop over parts of the
Western Gulf Coast and gradually expand northward over the
Central/Southern Plains by Thursday evening. Overnight Thursday into
Friday, the rain will move/expand into parts of the Middle/Lower
Mississippi Valley and parts of the Great Lakes. Rain will extend from the
Great Lakes to the Central Gulf Coast by Saturday.


Ziegenfelder


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