744
FXUS66 KSGX 212043
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
143 PM PDT Tue Oct 21 2025

.SYNOPSIS...
The marine layer will deepen and spread far inland
tonight, bringing patches of drizzle Wednesday morning.
Noticeable cooling Wednesday of as much as 12 to 18 degrees for
the mountains and far inland valleys, as well as stronger
southwest to west winds along and below the east slopes of the
mountains with gusts to 35-45 mph, up to 55 mph through the
passes. There is a slight chance of light showers Wednesday night
for the San Diego County coast and valleys as well as the San
Bernardino Mountains. High temperatures increase Thursday and
Friday. A low pressure system moving inland to the north will
bring cooler and breezy conditions for the weekend.

&&

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

.SHORT TERM...Today through Thursday...
Mid-level moisture is being advected northwards along the eastern
side of a mid-level low to the east of San Diego. This is
resulting in our current partially cloudy skies. These are based
around 12,000-15,000 feet and resulting in virga (precipitation
evaporating before it hits the ground due to dry air below the
clouds).

The low will move onshore south- central CA near Pt. Conception
Wednesday morning into the afternoon. This will have a few effects
on the local region, most noticeably a deeper marine layer that
will bring clouds much further inland than this morning, and much
cooler afternoon temperatures Wednesday anywhere from a few
degrees cooler than today (immediate coast) to 12-18 degrees lower
than today (mountains and western foothills). The deepening
marine layer will likely result in drizzle over the coasts and
valleys Wednesday morning.

This will also lead to stronger winds Wednesday afternoon and
evening, notably for the lee-side of the mountains/desert
foothills and the deserts, especially for those typically windy
gaps like the Banning Pass and the passes along I-8 near the east
mountain foothills as well as on the Imperial County line. Wind
gusts of 30-45 mph will occur throughout these areas, up to 55
mph through the passes.

As the low continues to the north of the region, there could be
some spotty light showers late Wednesday, most likely (10-15%) for
coastal San Diego County. The low continues into the desert
southwest Thursday morning, cutting off any shower chances and
leading to the weakening west winds in the deserts and desert
foothills turning weakly offshore Thursday morning through the
early afternoon (which means clear skies away from the immediate
coast and excellent visibility!). High pressure will start to
build into the region behind the low, and high temperatures will
start to increase again along with a shallower marine layer for
the end of the week.

&&

.LONG TERM...Fri Oct 24 through Tues Oct 28...
Ridging amplifies into Friday, and the mini warm-up will peak
Friday afternoon with high temperatures around 5 degrees above
average away from the immediate coast. The ridge will start to
flatten and move off to the east Saturday as a large trough drops
from the northwest. Model agreement is pretty good, with this
remaining fairly well to our north, but this will lead to cooling
temperatures this weekend and locally breezy winds (most likely
lee mountain foothills and deserts again), as well as the marine
layer deepening again. A few global ensemble members still have
light showers west of the mountains, but the large majority are
dry.

Some uncertainty with respect to the pattern next week, but some
form of ridging is more likely, which will bring warming
temperatures again, possibly to well above average.


&&

.AVIATION...
212000Z....Coast/Valleys...Patchy low clouds around 500 ft MSL will
linger at some beaches through the afternoon. Low clouds will push
ashore after 03Z this evening and head inland, filling the coastal
basin overnight into Wednesday. Initial bases will be 900-1500 feet
MSL, but rapidly rise above 2000 feet MSL by 16-17z Wednesday.

Otherwise...SCT-BKN clouds 12000-22000 feet MSL with VFR conditions
through the TAF period.

&&

.MARINE...
No hazardous marine conditions are expected through Sunday.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from 10 AM Wednesday to midnight PDT Wednesday
     night for San Diego County Deserts-San Gorgonio Pass near
     Banning.

PZ...None.

&&

$$

PUBLIC...CSP
AVIATION/MARINE...Villafane

NWS Tucson (SGX) Office