Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
154 PM EST Tue Dec 30 2025
Day 3
Valid 12Z Thu Jan 01 2026 - 12Z Fri Jan 02 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN CALIFORNIA...

...21Z Outlook Update...
The ongoing forecast philosophy is on track. Areas of 2-4 inch
rainfall amounts are expected during the first half of the forecast
period (12Z Thu through 00Z Fri) across the eastern Transverse
Ranges with slightly lesser amounts across the Los Angeles Basin
and Peninsular Ranges. Several instances of excessive runoff,
rock/mud slides, and flash flooding are expected.

See the prior discussion below for additional information.

Cook

...Previous Discussion...

A Slight Risk upgrade was introduced with this update, for many of
the same areas as the Day 2 Slight Risk. At the start of the period
New Year's morning, the brunt of the event will be well underway
across Southern California. Heavy rain will continue into the
morning hours as the surface low and upper level trough finally
move ashore during the day Thursday. Thus, the heaviest rains are
expected Thursday morning. Behind the low Thursday afternoon and
into the overnight, the rain should largely end for most, tapering
to a few showers here and there. Thus, this Slight Risk is really
for the first half of the day, and should be able to be dropped
after that. Nonetheless, an additional 1-2 inches of rain on top of
the rains from the overnight will continue to cause flooding
concerns across Southern California. So while amounts in total will
be less Thursday than on Wednesday, the continuation of Wednesday's
rain on into Thursday will keep the commensurate impacts ongoing as
well.

Further north, a Marginal Risk remains in place for portions of the
northern California coastal ranges and extending south along the
Sierra Nevada foothills. The rain in these regions Thursday and
Thursday night will be much more evenly spread in time. However,
these areas are much more equipped to handle the expected rain,
especially since full recovery from the Christmas rainfall event
has already occurred. An isolated instance or two of flash flooding
can't be ruled out, hence the Marginal, but overall impacts into
central and northern California should be minimal.

Wegman

Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt