311
FXUS66 KSGX 032052
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
152 PM PDT Wed Sep 3 2025

.SYNOPSIS...
Monsoonal moisture will remain in place through Thursday with
chances for afternoon and early evening thunderstorms for the
mountains, deserts, and inland valleys. Greater drying will occur
for Friday and Saturday with a slight chance of thunderstorms for
the mountains and deserts for Friday afternoon. The drying will
continue into early next week along with a cooling trend with high
temperatures for next Tuesday a few to around 5 degrees below
average. Night and morning coastal low clouds will gradually
return through the weekend and spread locally into the far western
valleys late each night for next week.

&&

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

Tonight through Friday...

There is still some residual moisture around in the mid levels to
allow for a very slight chance of an isolated shower or thunderstorm
over the mountains, and possibly the deserts, this afternoon.
Otherwise, skies will continue to remain mostly clear throughout
most of the evening, with the marine layer forming fairly late over
the coast inner waters of the SoCal bight, and then this will fill
into the coastal and inland areas, extending to around 5 to 10 miles
inland in most cases. There could also be some areas of patchy fog
during the early morning hours, especially within some of the wind-
sheltered valleys along the I-15 corridor. There will be a slight
better moisture surge tomorrow from the southeast, given that there
is currently a tropical system right off the coast of southern Baja
California, which will help to send some more moisture our way for
tomorrow. MUCAPE values will still be favorable to support vertical
growth and therefore thunderstorms will be more likely tomorrow,
mainly due to the increased moisture at the 700 mb level and
orographic lifting. As the ridge continues to slightly break down
and slowly retreat back towards the east, there will be a decreasing
chance of afternoon thunderstorms on Friday. Temperatures will also
begin a gradual cooling trend.

Weekend through next Tuesday...

The breakdown of the ridge, and more influence from the troughing
upstream over the eastern Pac Waters, will allow for conditions to
become relatively drier for SoCal beginning Saturday, with possibly
only a isolated shower or two over the mountains, and even lesser
chance of a storm. This will continue into early next week with a
consensus of both of the ensemble and deterministic models
displaying that the troughing will become the more dominant
feature, leading to increasing marine layer with more persistent
onshore flow, and temperatures remaining right around the seasonal
average (or even slightly cooler) going into Tuesday of next
week.

&&

.AVIATION... 032000Z...Coast...VFR through the afternoon with some
high clouds above 10kft. Patchy low clouds with bases 600-900 ft MSL
will push up to 5 miles inland along the San Diego coast generally
after 10Z Thursday, with clearing likely by 16z. VFR will prevail
there after.

Valleys/Mountains/Deserts...Clouds are building over the mountains
with bases 9000 feet MSL and a chance of SHRA/TSRA through 01Z. TSRA
tops to 35000 feet. Gusty and erratic winds, blowing dust with low
visibility, and lightning will accompany any TSRA, along with lower
bases 6000-9000 feet MSL. Mostly clear with VFR after 05z Thur.
SHRA/TSRA chances return for Thursday afternoon with chances slowly
increasing from 18z-01z.

&&

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

&&

.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...Stewey
AVIATION/MARINE...Villafane

NWS Tucson (SGX) Office