132
FXUS66 KSGX 101902
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
1202 PM PDT Thu Sep 10 2026

.SYNOPSIS...
The hot and humid high pressure system over the desert southwest
will continue to weaken into the weekend. Hot conditions this
afternoon will bring a cooling trend with lower humidity over the
next few days as an area of low pressure is expected to move
through the West Coast by the weekend. Monsoonal moisture hangs on
for one more day this afternoon with a slight chance of
thunderstorms across the mountains and adjacent deserts. The weak
troughing pattern will stick around into at leat the first half
of next week, bringing a deeper marine layer and cooler weather.

&&

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

Another hot day out there as high pressure continues to dominate
the desert southwest. Weakening is seen in this system today
though, as observations show better onshore flow closer to the
coast. This is keeping temperatures a bit cooler than at this
time yesterday with more places in the 80s instead of the 90s, so
the high temperature forecast may be overdone in some places. One
last chance for thunderstorms will occur later this afternoon
across the mountain spine from the Mexican border to Big Bear, as
well as some of the desert areas. Chances for precip range from
20-40 percent.

A troughing pattern begins to develop over the West Coast by
Friday, which will help weaken the high pressure system further
and bring in more cooling. High temperatures were raised slightly
from the previous forecast, but still shows a steeper decline in
temperatures mainly west of the mountains from 5-10 degrees cooler
than today. A stronger low pressure system develops from this
troughing pattern to the north, swinging through the Pacific
Northwest this weekend. This will bring further cooling to our
region with temperatures lowering closer to normal for the middle
of September. Welcome highs in the 80s/90s for western valleys,
most mountain areas, and locales in the high desert can be
expected. Overnight temperatures and humid conditions will also
decrease into the weekend as well as drier southwest flow moves
into our area. Morning temperatures in the 70s will be replaced
with 60s west of the mountains making it feel much more
comfortable for us. The marine layer will also slowly return for
coastal and western valley areas over the next few days as well.

The area of low pressure moves out of the Pacific Northwest by
Monday, leaving behind a weak troughing pattern over the region
for at least the first half of next week. This will bring similar
temperatures each day with highs and lows near to slightly below
average with dry weather.

&&

.AVIATION...
101815Z...VFR conditions expected across the region through this
evening, with FEW clouds between 10-20 kft and SCT cumulus over
mountains. ISO SHRA/TSRA over mountains and near desert slopes 19-
00Z, with CB clouds based 8-12 kft MSL and tops rising to 30 kft.
Localized gusty winds and heavy rain in and near any TSRA. Areas of
coastal low clouds based 600-1000 ft MSL and fog will gradually
increase after 07Z Friday, with cigs most likely 11-16Z Friday in
vcnty KSAN and patchy cigs 13-16z in vcnty KCRQ. Vis 1-5SM over
higher coastal terrain. FG and vis 0-1SM locally in valleys east of
I-15 (SD County) above 600 ft MSL. Scatter out 16-18z Fri.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Extreme Heat Warning until 8 PM PDT this evening for Orange
     County Coastal Areas-Orange County Inland Areas-San
     Bernardino and Riverside County Valleys-The Inland Empire-
     San Diego County Coastal Areas-San Diego County Valleys-
     Santa Ana Mountains and Foothills.

     Heat Advisory until 8 PM PDT this evening for Riverside County
     Mountains-San Diego County Mountains.

     Extreme Heat Warning until 8 PM PDT Friday for Coachella Valley-
     San Diego County Deserts-San Gorgonio Pass near Banning.

PZ...None.

&&

$$

PUBLIC...APR
AVIATION/MARINE...Westerink

NWS San Diego (SGX) Office