615
FXUS66 KSGX 081453
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
753 AM PDT Mon Sep 8 2025

.SYNOPSIS...
A low pressure system will gradually bring cooler weather this week
and temperatures will be mostly below normal. This system will also
boost winds in parts of the mountains and deserts during afternoons
and evenings. The marine layer will rebuild to provide increasing
nocturnal low cloudiness west of the mountains.

&&

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

.Morning Update...

As of 7:30 AM, mostly clear skies with some patchy low clouds near
the coast. These low clouds should clear in the next few hours and
give way to mostly clear skies region-wide. Robust west winds are
expected this afternoon, especially for the mountain ridges, desert
slopes and high deserts with gusts 25-40 mph, locally up to 45 mph
through the San Gorgonio Pass. The forecast remains on track for
strong afternoon west winds through Thursday as the upper level low
spins around its axis and weak dry shortwaves move through.



.Previous Discussion (315 AM PDT Sunday)...


A pretty cohesive low cloud deck is gradually approaching the coast
as we play a waiting game to see how much land is covered before
sunrise. Expect some coastal areas to wake up to clouds, other
coastal areas to the sun. Today will be seasonably warm, down from
yesterday as a cooling trend gets underway. A low pressure trough,
rather deep and amplified for this time of year, hangs off the
Pacific NW coast. This will gradually sink southward down the coast,
right over California Tuesday through Thursday. Accordingly, the
marine layer will deepen and coastal cloud coverage will expand in
time and space each day. Tonight into Tuesday it should reach into
western valleys, with some true fog (low visibility) on the inland
edge of the cloud deck. By Wednesday morning the cloud deck should
fill the entire coastal basin, maybe flush into the foothills. We
should have a similar coverage for Thursday. With the deep marine
layer we could get a very thick cloud deck, which would produce
drizzle those days. However, the cooler air aloft would weaken the
marine inversion greatly, and could prevent the cloud from
thickening enough for drizzle. Onshore winds will pick up this
afternoon and evening as the trough makes its move southward. The
usual wind-prone mountain passes and adjacent desert slopes will get
the strongest winds each day. Strongest winds appear in those spots
for Tuesday afternoon and evening, with gusts 50-60 mph.
Temperatures today will be near normal, but decrease each day into
Thursday, likely our coolest day this week. Max temps Thursday will
be in the 70s west of the mountains, with only a few spots in the
Inland Empire reaching 80 degrees. It should be around 80 in the
high desert and low 90s in the low desert. And 50s and 60s in the
mountains. These temps are generally 10-15 degrees below normal
inland, even as much as 20 degrees below normal in the mountains. It
might be time to dust off the jackets. The trough over the West
begins to weaken and lift out Friday through the weekend, so the
reverse trend is expected: warmer weather, a shallower marine layer,
and weaker winds. Still, forecast temps this weekend don`t quite
reach normal. Monsoon moisture and thunderstorms will become a
distant memory as dry westerly flow prevails this entire week.

&&

.AVIATION...
081500Z...Coast/Valleys...Patchy low clouds based 600 ft MSL are
clearing out of coastal SD County. Clear skies otherwise. Low clouds
based 1000-1500 ft MSL return to coastal San Diego County after 03Z
Tuesday and spread northward and inland overnight. 40% chance for
cigs at KONT after 12z.

Mountains/Deserts...VFR conditions prevailing through Tuesday
morning.

&&

.MARINE...
Northwest winds gusting to 20 kts near San Clemente Island in the
afternoon and evening hours on Monday and Tuesday. Otherwise, no
hazardous marine conditions are expected through Friday.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.

&&

$$

PUBLIC...Westerink/MM
AVIATION/MARINE...Westerink

NWS Tucson (SGX) Office