443
FXUS66 KSGX 090416
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
916 PM PDT Fri Aug 8 2025

.SYNOPSIS...
Hot conditions will continue into early next week with widespread
moderate HeatRisk across the Inland Empire, mountains, and High
Desert, and widespread major HeatRisk in the low desert.
Conditions will gradually cool to near or slightly below normal by
the end of next week. The marine layer will deepen slightly and
become more widespread across the coast and western valleys
tonight into Saturday. The marine layer is expected to deepen
further later next week.

&&

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

Today was noticeably cooler than yesterday across the region, especially
in the inland valleys of San Diego County where temperatures were as
much as 10-15 degrees lower than yesterday. Some locations in the
lower deserts were as much as 6 degrees cooler than yesterday. A
stronger sea breeze which pushed moist marine air into the San
Diego County valleys was likely responsible for the temperatures
there, and a surge of moisture from the Gulf of California is most
likely responsible for the lower temps in the low deserts. Dew
point temperatures in the low deserts today are as much as 20
degrees higher than they were yesterday afternoon. Around 6 pm, a
couple of convective cells rapidly developed over the Borrego
Desert and produced some lightning flashes before weakening and
finally dissipating. There were no reports of precipitation or
gusty winds from these cells. The presence of low-level moisture
in the Borrego Desert and Imperial Valley suggest a non-zero
chance for isolated convection again tomorrow. The marine layer is
a little deeper than at this time yesterday and the low clouds
are much more extensive. They have already spread a few miles
inland, covering much of the coastal areas. Low clouds and fog
could locally spread as much as 10 miles inland by sunrise.

From previous discussion...
Ensemble guidance is indicating an increase in
precipitable water for the lower deserts on Saturday, which would
result in a lower high temperature reading. That will quickly be
followed by a decrease in precipitable water for early next week.
Chances of exceeding 110 degrees on Saturday in the low desert are
80 to 90 percent, with chances increasing to 95 to 100 percent for
Sunday through Tuesday. Chances of exceeding 115 degrees are 30 to
40 percent Sunday through Tuesday and under 15 percent for Saturday.
Current forecast has high temperatures 110 to 115 degrees into early
next week and maintains fairly widespread major HeatRisk.

The marine layer will deepen slightly over the weekend and become
more uniform in coverage. That should help moderate temperatures for
the coast, inland Orange County, and San Diego valleys. The marine
layer is not expected to deepen enough to reach into the Inland
Empire, maintaining areas of moderate HeatRisk through the weekend.
High pressure aloft combined with a shallow marine layer will
maintain hot conditions in the mountains. Highs there will be in the
80s to 90s with widespread moderate HeatRisk. If you`re planning to
be outside over the weekend in the Inland Empire, mountains, or
deserts make sure you stay hydrated and seek plenty of shade if
you`re doing recreational activities.

A gradual cooling trend will prevail next week. By Tuesday, high
temperatures will be near normal west of the mountains and 5 to 8
degrees above average in the deserts. High temperatures on
Thursday will be a few to around 5 degrees below average for the
coast and valleys and a few degrees above average for the deserts.
Widespread near to below average temperatures are expected by
Friday. Night and morning coastal low clouds will spread into the
far western valleys late each night.

&&

.AVIATION...
090300Z....Coasts...Low clouds based 700-1200ft MSL are building in
coastal areas, expected to push up to 10 miles inland through 12z
Sat. VIS reductions are likely along coastal terrain and in some
valleys. Clouds clear to the coast around 17z and return with
slightly higher bases between 02-04z Sun.

.Valleys/Mountains/Deserts...Hazy but VFR through tomorrow evening.

Smoke from area fires, mostly the Gifford Fire in Santa Barbara
County, will continue to be present at or above 10,000 feet MSL.
Surface conditions hazy but still VFR.

&&

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

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 8 PM PDT Monday for Riverside County
     Mountains-San Bernardino County Mountains-San Bernardino
     and Riverside County Valleys-The Inland Empire-San Diego
     County Mountains.

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

PZ...None.

&&

$$

PUBLIC...PG
AVIATION/MARINE...Westerink