Placentia, California Weather Forecast Discussion

854
FXUS66 KSGX 262052
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
152 PM PDT Fri Sep 26 2025
.SYNOPSIS...
There is a slight chance of showers and thunderstorms this afternoon
in the mountains and deserts. Chances for showers and thunderstorms
increase on Saturday for the mountains and deserts and expand to the
inland valleys during the afternoon. 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
the week.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
A closed low pressure system will move south and linger along the
Southern California border with northern Baja Saturday. The low is
expected to weaken and move to the east on Sunday. There is a 15 to
25 percent chance for showers and thunderstorms for the mountains
and deserts this afternoon as moisture and instability spreads into
the area from the north. 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 are 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 to exceed one inch an hour,
most likely in the mountains. Areas of flash flooding 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 lower
than Saturday, with high resolution guidance showing rainfall rates
below 0.50 inches 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...
262030Z....Coasts/Valleys/Foothills...SCT-BKN clouds based at 4000-
5000 feet MSL remain over the entire coastal basin. Cigs will return
to widespread BKN-OVC conditions between 02-04z Sat, based at 2000-
3000 ft MSL, then rising mostly above 3000 ft MSL overnight. Some
random scattering of clouds possible after 16z, clearing gradually
throughout the late morning and afternoon. Slight chance for
SHRA/TSRA after 19z Sat for the mountain foothills, eastern Inland
Empire and eastern San Diego County valleys.
Mountains/Deserts... 20% chance of TSRA 19-01Z across mountains and
high desert this afternoon. Bases around 10000 feet MSL and storm
tops to 30K feet. An isolated SHRA/TSRA is also possible (20-30%
chance) overnight into early Saturday, mainly along desert slopes
but also in the vicinity of lower desert communities. More scattered
SHRA/TSRA acivity is expected (50-60% chance) across mountains and
deserts after 18z Sat. Any thunderstorm could produce frequent
lightning 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 7 feet.
&&
.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...CO
AVIATION/MARINE/BEACHES...Westerink

NWS SGX Office Area Forecast Discussion