Fullerton, California Weather Forecast Discussion

479
FXUS66 KSGX 270422
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
922 PM PDT Fri Sep 26 2025
.SYNOPSIS...
Scattered showers and the occasional thunderstorm will move
southwest across the region from the Mojave Desert through
tonight. Showers could reach the coastal areas but any
precipitation that reaches the ground will be light. Chances for
showers and thunderstorms increase on Saturday for the mountains,
deserts and inland valleys during the afternoon. Chances for
showers and thunderstorms decrease for Sunday, and Monday is
likely to be dry. There will be a brief warming trend through the
weekend with cooler conditions again on Tuesday. Along with cooler
conditions, increased southwest to west winds for the mountains
and deserts and cloud coverage can be expected Tuesday. A gradual
warming expected Wednesday through the rest of next week.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
This evening...showers and thunderstorms moved into southwestern
San Bernardino County from the northeast in the return flow on the
northwest side of the low pressure system now centered roughly
over Riverside County. The storms weakened as they moved into a
more stable environment and currently, they are no longer
producing lightning. Any precipitation reaching the ground will be
light. The storms produced some strong convective winds in the
high desert but the gusts were somewhat masked by the generally
strong synoptic winds produced by the low pressure system. Light
showers, and possibly an occasional tstm will continue moving
across the region from northeast to southwest overnight into Sat
morning. Light showers may even reach the coast at times. Today
was noticeably cooler than yesterday, with temperatures in the
inland valleys barely reaching the low 80s. A few inland valley
locations were as much as 13 degrees cooler than yesterday.
From previous discussion...
As the center of low moves to the border of Southern California
and northern Baja Saturday, an influx of moisture will spread into
the area from the east. This will bring an increased chance of
showers and thunderstorms for the mountains, deserts, and valleys.
The greatest chances will be for the mountains and deserts of 30
to 60 percent during the afternoon. For areas west of the
mountains, chances are closer to 25 to 40 percent for the valleys
and near 15 percent for the coast. High resolution guidance is
indicating rainfall rates will be mostly 0.50 to 1 inch per hour
with the potential for isolated rates exceeding one inch an hour,
most likely in the mountains and on the desert slopes. Areas of
flash flooding will be possible for the mountains, deserts, and
inland valleys.
The low pressure system will weaken and move east on Sunday with a
10 to 20 percent chance of showers and thunderstorms for the
mountains and deserts on Sunday afternoon from lingering moisture
and instability. Rainfall rates on Sunday are expected to be
significantly lower than Saturday, with high resolution guidance
showing rainfall rates below 0.50 inch an hour. Dry conditions
are expected by Monday.
The coast and valleys are expected to see a few degrees of warming
on Saturday, with a few degrees of cooling in the mountains and
deserts. Most areas will be a degree or two warmer on Sunday, with
continued warming into Monday. An incoming trough of low pressure
will begin to influence our weather on Tuesday, bringing cooler
conditions with increased cloud coverage and winds in the mountains
and deserts. High temperatures on Tuesday will mostly be 5 to 10
degrees below average for inland areas to locally 10 to 15 degrees
below average for the higher elevations of the mountains. This will
be followed by slow warming through the rest of the week with high
temperatures on Thursday still a few degrees below average for
inland areas.
&&
.AVIATION...
270330Z....Coasts/Valleys/Foothills...SCT-BKN clouds with varying
bases from 2000-4000 feet MSL will become a more widespread BKN-OVC
overnight. Low clouds slowly scatter out for most areas between 17-
20Z. Slight chance for SHRA/TSRA after 19z Sat for the mountain
foothills, eastern Inland Empire and eastern San Diego County
valleys. Low clouds based 2000-3000 ft MSL redevelop for the inland
valleys and foothills around 03-06Z Sunday, then expand to cover the
coastal basin overnight.
Mountains/Deserts...An isolated SHRA/TSRA is also possible (20-30%
chance) overnight into early Saturday, mainly along desert slopes.
More scattered SHRA/TSRA activity is expected (50-60% chance)
across mountains and deserts after 18z Sat. Any thunderstorm could
produce frequent lightning, reduced cigs/vis, and locally erratic
winds.
&&
.MARINE...
No hazardous marine conditions are expected through Tuesday.
&&
.BEACHES...
South swell from Hurricane Narda will arrive this weekend. Swell of
4-5 feet with a period of 12-14 seconds will produce elevated surf
and a high rip current risk Sunday through Tuesday, especially for
south facing beaches, where sets could reach 8 feet. More
information can be found in our Beach Hazards Statement, which is in
effect from 13Z Sunday until 06Z Wednesday.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement from Sunday morning through Tuesday
     evening for Orange County Coastal Areas-San Diego County
     Coastal Areas.
Flood Watch from Saturday morning through Saturday evening for
     Riverside County Mountains-San Bernardino County Mountains-
     San Diego County Mountains.
PZ...None.
&&
$$
PUBLIC...PG
AVIATION/MARINE/BEACHES...KW

NWS SGX Office Area Forecast Discussion