DesertWeather.com

211
FXUS66 KSGX 010547
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
1047 PM PDT Wed Sep 30 2026

.SYNOPSIS...
Strengthening high pressure aloft will bring a warming trend with
a long-duration heat wave likely for this weekend through much of
next week into the following weekend. The highest HeatRisk is
expected for the coast and valleys with widespread Moderate or
greater HeatRisk for the coast and valleys for Friday through next
week with widespread Major to Extreme HeatRisk for the weekend
into next week for inland coastal areas into the western valleys.

&&

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

...UPDATED AVIATION DISCUSSION...

Tonight through Thursday...

A ridge is building back in over the region as the upper level low
that was positioned over Arizona continues to propagate eastward.
This is going to allow for the positively-tilted ridge to continue
to expand back towards the northeast. This will result in
temperatures gradually increasing through Thursday. Gusty northerly
winds will continue to diminish as the low pulls away, but remain
gusty each afternoon through tomorrow, especially within the San
Gorgonio Pass. For tonight, there will be a little better onshore
flow this evening, which will allow for the marine layer to likely
set in a little sooner and also fill in better into the inland
areas. Ceilings will begin to lower a bit throughout the night, and
there may also be some areas of patchy fog along the I-15 corridor
again, as there was this morning. For tomorrow, highs will be around
10 to 15 degrees above the seasonal average, and relative humidities
will still be relatively higher at night, and therefore nights will
still be close to average.

Friday through Wednesday...

By Friday, the ridge is going to continue to strengthen to heights
of 590 dm over the region, which is going to cause temperatures to
max out generally around 15 to 20 degrees above the seasonal
average. This, in combination with increasing RH values, which will
not allow for radiational cooling to cool temperatures as much, will
produce conditions that may be impactful for those sensitive to
those vulnerable to heat, especially for those along the coastal
areas that do not have AC units. For this reason, an Extreme Heat
Watch has been issued for the coastal and inland valleys from Friday
through the mid part of next week. Temperatures are going to become
even hotter for this upcoming weekend, and on Sunday there will
be easterly winds as the position of the high slides further south
over the desert southwest by Sunday. These offshore winds will
likely result in highs being even further warmer to the coast.
These gusty easterly downsloping winds will also reduce RH values
down into the 15-25% range for the inland areas and elevate fire
concerns. As the ridge remains locked in place going into the mid
part of next week, so will the heat, and there will not be much
relief from this looking into the foreseeable future until the
ridge begins to finally break down.

&&

.AVIATION...
010545Z...Coast/western valleys: Patchy low clouds based near 600-
1000 ft MSL have formed along parts of Orange Co, though they remain
largely offshore of SD Co. Clouds gradually become more uniform in
coverage and press inland after 08Z or so, and bases may lower
slightly through the early morning. Areas of vis reductions (1-5SM)
expected for elevated coastal terrain and western valleys (I-15
corridor). Clouds scatter back toward the coast 15-17Z. Clouds will
be far patchier and intermittent when they reform late Thursday
evening, impacting coastal sites late if they do (30-50% chance for
cigs).

Otherwise...clear skies through Thursday.

&&

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

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Extreme Heat Watch from Friday morning through Wednesday 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.

PZ...None.

&&

$$

PUBLIC...Stewey
AVIATION/MARINE/BEACHES...CSP