755
FXUS66 KSGX 222051
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
151 PM PDT Fri Aug 22 2025

.SYNOPSIS...
High temperatures will remain above average through the weekend,
but with slight cooling Saturday and Sunday. More noticeable
cooling next week with high temperatures near or a little below
seasonal averages for next Tuesday through Friday. There are
chances for showers and thunderstorms over the mountains and
deserts each afternoon and evening into next week with the greater
chances for Saturday through Wednesday. Night and morning coastal
low clouds will remain patchy through the weekend and limited
mostly to coastal areas.

&&

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

This afternoon...cumulus clouds have developed over the mountains
and the steering flow is forcing them off the ridgelines over the
valleys and high deserts. So far there is very little vertical
development in the cumulus clouds and the chances for
showers/tstms remains low for this afternoon. At this hour
temperatures are mostly a few degrees lower than at this time
yesterday including in the lower deserts. Low clouds and fog from
the shallow marine layer are hanging around the beaches in some
places.

Some high-resolution models are showing an easterly wave with the
potential to bring some elevated showers/tstms to SoCal overnight
tonight. Significant rainfall from these showers is unlikely but
the cloud cover from this disturbance could have implications for
temperatures through the weekend.

The high pressure will remain largely unchanged through Sunday
before weakening and shifting early next week. Through
Sunday...high temperatures will remain above seasonal averages,
although there will be a few degrees of cooling Saturday and
Sunday. High temperatures for today will be around 5 to 10 degrees
above average for inland areas, ranging from the upper 90s to 106
for the Inland Empire and for the Apple and Lucerne Valleys, and
110 to 114 for the lower deserts. High temperatures for Sat and
Sun will be around 5 degrees above average for most areas. The
most likely locations to tie or exceed daily high temperature
records for today will be in the mountains. It`s more likely that
locations will tie or exceed existing daily records for record
warm overnight low temperatures through the weekend for the
mountains, lower deserts, Inland Empire, and inland Orange County.

The marine layer will remain around 1000 feet deep through the
weekend with night and morning coastal low clouds remaining patchy
and limited mainly to coastal areas.

Monsoonal moisture will increase into Saturday, then decrease
slightly on Sunday. There will be chances for afternoon and early
evening showers and thunderstorms, mostly for the mountains and
deserts each day with the greater chances on Saturday and Sunday.
There could also be some elevated convection for tonight into
Saturday morning moving along in the south to southeast flow
aloft. This could affect areas west of the mountains as well.

Any rainfall through Saturday morning is expected to be
insufficient for flash flooding. For Saturday afternoon and early
evening, thunderstorms could cause isolated flash flooding, mainly
for the San Bernardino Mountains, the Riverside County mountains,
and the Lucerne Valley. Not much change in the flash flood threat
is expected on Sunday. The strength of the steering flow will keep
the convective elements moving at speeds of 20 mph or more and
will also likely prevent them from remaining anchored to terrain.

High temperatures on Monday will be a few degrees cooler than
Sunday, mostly near to a few degrees above average on Monday. A
surge of lower level moisture into the deserts on Monday night and
Tuesday could bring greater cooling on Tuesday high temperatures
as much as 5 to 10 degrees cooler for the lower deserts. The high
begins to weaken and become displaced to the southeast in response
to a trough developing over the west coast. This will bring
generally lower temperatures with most areas several degrees
cooler than seasonal averages for Tuesday through Friday.

With the additional influx of moisture, NBM daily chances for
one-half inch or more of rainfall at Big Bear increase to 30
percent on Tuesday. Chances for mainly afternoon and early
evening showers and thunderstorms will decrease for Wednesday
through the rest of next week as the flow aloft turns
southwesterly and moisture decreases.

&&

.AVIATION...
222010Z...Coast/Valleys...Low clouds and fog along the coast,
generally in San Diego Co. Cigs 400-800 ft MSL with vis restrictions
2-5 SM but locally 0-3 SM for higher coastal terrain.

Low clouds and fog moving inland after 23/04Z with a 60% chance for
impacts at KSAN. Chances for stray TSRA/SHRA moving in from the east
late this evening through Sat morning, highest (15-20%) in inland
valleys with 10-15% chance for western valleys and coastal areas.

Mountains/Deserts...SCT-BKN clouds 15-20kft MSL. TCU/CB formation
with bases around 7-9kft MSL expected during afternoon hours over
the mountains, with 30-40% probability for TSRA over the mountains,
and a 15-25% chance for the deserts this afternoon/evening. Lower
but still chances continue overnight into early Sat morning.
SHRA/TSRA could bring restricted VIS down to 1-3SM at times, along
with gusty and erratic winds, dangerous cloud-to-ground lightning,
and possible small hail.

&&

.MARINE...
Low (about 10% chance for nearshore waters) chance for showers or
thunderstorms to move west over the nearshore waters late this
evening through Saturday morning. Otherwise, no hazardous marine
conditions are expected through Tuesday.

&&

.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 Saturday for Orange County Inland
     Areas-San Bernardino and Riverside County Valleys-The
     Inland Empire-San Diego County Valleys-Santa Ana Mountains
     and Foothills.

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

     Extreme Heat Warning until 8 PM PDT Saturday for Apple and
     Lucerne Valleys-Coachella Valley-San Diego County Deserts-
     San Gorgonio Pass near Banning.

PZ...None.

&&

$$

PUBLIC...PG
AVIATION/MARINE...Small