633
FXUS66 KSGX 212100
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
200 PM PDT Fri Aug 21 2026

.SYNOPSIS...
Monsoonal moisture will decrease into the weekend with a slight
chance of showers and thunderstorms for the mountains and high
desert for this afternoon. Above average high and low temperatures
will continue through next week. Widespread moderate to locally
major HeatRisk for the coast, valleys, and mountains except near
the beaches and for the higher elevations in the mountains, with
major to extreme HeatRisk for the lower deserts.

&&

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

Outside of a few passing high clouds, most of the region is
experiencing sunshine this afternoon. Cumulus clouds over San
Gorgonio mountain have grown into showers and a thunderstorm. PWAT
values in this mornings sounding have actually increased a bit from
yesterday and thus there is still an outside (10%) chance for shower
development where cumulus have already developed over the Peninsular
Range later this afternoon.

As of 1 PM, about 50% of temperature observations read 100F or above
through the Inland Empire with readings approaching 100F through the
interior and foothill valleys of San Diego County. Temperatures near
the coast remain closer to average with more comfortable mid 70s
across the San Diego County Coast and low 80s across the Orange
County coast.

This morning`s marine layer was slow to develop and quite shallow -
around 1000 feet deep with patchy cloud cover and locally lower
visibilities in the valleys surrounding the I-15 corridor. This
pattern should continue in the coming days as the ridge continues to
squash the boundary layer.

Long range models are in solid agreement about keeping the upper
level ridge strong and centered over the Desert Southwest for at
least the next week, despite the jet stream flowing north of it
across the Northwest. As a result, model guidance is foresting
temperatures consistently 5 to 10 degrees above average across
Southern California through the forecast period with little day-to-
day change. Given we are in an already hot time of year, impacts
from prolonged above normal heat will be more widespread. Most
inland areas will experience moderate HeatRisk through next week
with some areas of Major HeatRisk. The lower deserts will experience
persistent Major HeatRisk through next week with temperatures
forecast 110-115F everyday of the forecast period and low
temperatures struggling to fall below 90F in some places.

Despite the favorable positioning of the ridge, thunderstorm
chances are limited this weekend and increasingly less impressive
next week with less moisture in store. Chances are subject to
change however, especially next week, as the mid-level flow
remains generally southerly with the upper level high pressure
spinning to the east.

The Extreme Heat Warning continues for the lower deserts through
next Friday and a Heat Advisory is now in place for the inland
valleys and mountains (below 6000 feet in San Bernardino County)
from Saturday morning through Monday evening. Take breaks in the
shade, hydrate and seek A/C when possible!

&&

.AVIATION...
211800Z...Coast...VFR conditions expected this afternoon with SCT
high clouds AOA 20 kft. Patchy low clouds reforming after 08Z near
the beaches, with low to moderate confidence in cigs near 400-900 ft
MSL impacting coastal SD County TAF sites between 11-15Z Sat. Low
clouds scatter thereafter.

Otherwise...FEW to SCT clouds above 20 kft MSL through Friday.
Slight chance (10-15%) for ISO SHRA/TSRA over mtns from 20z Fri to
01z Sat.

&&

.MARINE...
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 from 10 AM Saturday to 8 PM PDT Monday for Orange
     County Inland Areas-Riverside County Mountains-San
     Bernardino County Mountains-San Bernardino and Riverside
     County Valleys-The Inland Empire-San Diego County Mountains-
     San Diego County Valleys-Santa Ana Mountains and Foothills.

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

PZ...None.

&&

$$

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