River Flood Warning 1, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
203 AM PST Thu Jan 1 2026

.SYNOPSIS...
Scattered light showers this evening will increase in coverage and
intensity Thursday morning, with chances for thunderstorms
Thursday morning and afternoon. Showers taper off late Thursday. A
period of drier weather will occur on Friday. A series of weak
but colder weather systems will bring more chances for light to
moderate showers over the region for this weekend into the middle
of next week.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

Today through tomorrow...

An upper level low continues to propagate up from the south, which
is currently located around 750 miles to the northwest of San Diego.
This will continue to produce more showers moving onshore from the
southwest throughout a good portion of the day. An associated cold
frontal boundary will also push through by later in the afternoon,
and will help to provide some additional instability, so there will
likely be a line of more moderate to heavy showers along the leading
edge, with even the slight chance of a thunderstorm. As this feature
continues to transition up towards the north, with the a major
shortwave trough advancing in towards California, which will help to
force the cut off to move northward and become absorbed into the
ridge downstream. More moisture being advected up ahead of the
approaching trough will keep the chance of showers going into
Friday, although there will be somewhat of a break in between the
two systems, and therefore a lesser chance. Temperatures with the
southerly flow will remain on the more mild side for this time of
year, although highs will be notably cooler today as compared to
yesterday. Through tomorrow morning, additional rainfall rates are
expected to be from around 0.5 to 1 inch for the coastal and inland
areas, with an inch to 2.5 inches possible for the mountains, and
around 0.10-0.25 inches for the lower deserts, to 0.25 to 0.5 for
the high deserts. Some of these areas have already been inundated
with copious amounts of rain from last week, and given expected
rainfall rates, this might lead to some areas having a risk of
flooding. Please see the Flood Watches currently active, which
further highlights these details.

Saturday through Wednesday...

The major shortwave trough upstream will continue to move in across
the region throughout the weekend, with a steady band of rain
pushing through by later in the evening on Saturday and into Sunday
morning. The positively tilted axis with this trough will allow for
a secondary wave to deepen in its wake going into the early part of
next week with yet another trough moving in. This is where
deterministic models begin to diverge more with the progression of
the secondary trough. Some of the models (such as the ECMWF) have
this system transitioning through much quicker, with a drier
solution, whereas the GFS have the low deepening right over southern
California, with a much better chance of precipitation occurring.
The will continue to be evaluated in the upcoming days to see which
model is resolving this feature the best, but it is safe to say the
the overall active weather pattern will continue through at least
the mid part of next week, as ensemble members suggest.

&&

.AVIATION...
011000Z...BKN-OVC clouds based 1000-2000ft MSL for most locations.
-RA continues to move in from the southwest, spreading over the
region and bringing brief VIS drops to 1-3SM in RA. Southerly winds
increase this morning with gusts 20-30 kt for the coast and valleys
and 30-50 kt along the northern slopes of the mtns, weakening after
20z Thur. Precipitation may form into organized bands of +RA which
would move across the region from west to east beginning 15-18z Thur
and prevailing through 01z Fri, bringing IFR CIGs/VIS. There is a
40% chance for TSRA for areas mountains westward (~10% chance vcnty
KPSP) from 12z through 00z Fri, highest chances 14-22z Thur. RA
should generally end by 02z Fri, with only -SHRA lingering in San
Diego County beyond this point. CIGs should return VFR after 04z Fri
everywhere outside of localized SHRA.

&&

.MARINE...
Southeasterly winds with gusts 20 to 25 knots peak this morning and
steep mixed seas 4 to 7 feet through the coastal waters. In
addition, the incoming storm system will bring a chance for
thunderstorms this morning and early afternoon. Any thunderstorm
that develops will bring strong gusty winds, lightning, and brief
heavy rain that will lead to poor visibility. There is also a slight
chance for waterspouts.

Winds diminish this afternoon and evening. Then, no hazardous marine
weather conditions expected through Sunday, though there will be
periods of breezy south winds through the weekend.

&&

.BEACHES...
There is a slight chance for thunderstorms and associated lightning
risk today, highest chances in the morning and early afternoon. If
you see lightning or hear thunder, seek a sturdy, enclosed shelter.
Additionally, starting Thursday morning and continuing through the
weekend, high tides of 6.5 to 7 feet could lead to minor coastal
overflow/flooding for beaches and flood-prone beach lots and
walkways.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through Sunday morning for Orange County
     Coastal Areas-San Diego County Coastal Areas.

     Flood Watch through this evening for Orange County Coastal Areas-
     Orange County Inland Areas-San Bernardino County Mountains-
     San Bernardino and Riverside County Valleys-The Inland
     Empire-Santa Ana Mountains and Foothills.

PZ...Small Craft Advisory until 3 PM PST this afternoon for Coastal
     Waters from San Mateo Point to the Mexican Border and out
     to 10 nm-Waters from San Mateo Point to the Mexican Border
     Extending 10 to 60 nm out including San Clemente Island.

&&

PUBLIC...Stewey
AVIATION/MARINE...Zuber