360
FXUS66 KSGX 092052
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
152 PM PDT Tue Sep 9 2025

.SYNOPSIS...
A large low pressure system moving slowly into the western states
will bring stronger onshore flow, spreading cooling inland and
deepening the marine layer to around 3000 feet with night and
morning coastal low clouds covering most of the coast and valleys
for early tomorrow morning and early Thursday morning, with some
areas of light drizzle possible. Southwest winds during the
afternoon and evening will gust to 30 to 40 mph for the deserts
onto the desert slopes of the mountains. This will be followed by
warming for Friday and Saturday and additional warming for early
next week with the marine layer becoming shallower.

&&

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

Tonight through this weekend...

A broad longwave trough over the eastern Pacific is continuing to
slowly propagate towards the region and beginning to influence SoCal
with cooler temperatures and more of a persistent onshore flow with
the marine layer becoming more predominant and extending further
inland than in recent days. There will also be gusty afternoon winds
for the higher elevations of the mountains and deserts, especially
for the ridgetops and through the mountains gaps and passes. There
could be occasionally gusts up to 55 mph, or locally higher at times
within the Gorgonio Pass. There could also be some areas of blowing
dust possible, and this will continue throughout the early evening,
and then winds will begin to decouple and subside throughout the
night. They will increase again tomorrow afternoon for the same
areas, although they will likely remain below the threshold for a
majority of the period, and therefore Wind Advisories will not be
needed for tomorrow. Temperatures will also be notably cooler
tomorrow, and the coolest day of the week. There will be only a
slight and very gradual warmup going into the weekend coming up as
the trough begins to fill and retreats a little more to the north.
The marine layer will also thicken up a little more tonight with
increasing heights, and this may allow for there to be some areas of
drizzle, especially for the foothills during the early morning
hours.

Early through mid part of next week...

Both deterministic models and ensembles alike are displaying a
return of ridging early next week, which will allow for a jump in
high temperatures for next Monday, and then even further warming
going into the middle of next week. The marine layer will also begin
to thin and lower and high pressure builds in stronger going into
the middle of next week. Conditions also will continue to remain dry
throughout this period in the forecast.

&&

.AVIATION...
092100Z...Coast/Valleys...Low clouds with bases 2000-2500 feet MSL
to redevelop after 23Z and form inland overnight, filling the entire
coastal basin by 10z early Wednesday. Reduced vis  0-5SM for far
inland valleys and hills. Scatter out to the coast 17-19z Wednesday
with SCT-BKN cloud coverage sticking around throughout the afternoon
at the immediate coast.

Mountains/Deserts...Areas of gusts 35-45 mph ridgetops and desert
slopes this afternoon, locally up to 60 mph in mountain passes
through about 11Z Wednesday. Mostly clear and VFR conditions this
afternoon and tonight. Slightly less windy Wednesday afternoon.

&&

.MARINE...
Occasional northwest wind gusts exceeding 20 kt in vicinity of San
Clemente Island in the afternoons and evenings through Wednesday
night. Otherwise, no hazardous marine conditions are expected
through Saturday.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory until 1 AM PDT Wednesday for Apple and Lucerne
     Valleys-Riverside County Mountains-San Bernardino County
     Mountains-San Diego County Deserts-San Diego County
     Mountains-San Gorgonio Pass near Banning.

PZ...None.

&&

$$

PUBLIC...Stewey
AVIATION/MARINE...Westerink