886
FXUS66 KSGX 232033
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
133 PM PDT Sun Aug 23 2026
.SYNOPSIS...
Monsoonal moisture will decrease this weekend, with a slight
chance of showers and thunderstorms for the mountains and lower
deserts returning for Monday 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...
This morning`s marine layer was very shallow - around 500 ft deep
- with areas of fog between I-5 and I-15. Otherwise, yet another
day of summer sunshine is in store for the region with a few
cirrus clouds passing by. Low clouds are expected to redevelop
later this evening, bringing patchy dense fog to coastal areas and
western valleys overnight tonight. The marine layer will compress
even more throughout next week, yielding overnight fog mainly to
coastal areas and perhaps down to the beaches.
While southwesterly flow aloft is not the most ideal setup for
monsoonal moisture, thunderstorm chances return for early this week.
Pulses of higher PWAT`s above 1.3 inches are forecast to move over
our mountains early Monday through Tuesday afternoon. While some
long range models continue to show no precip throughout the week,
high resolution guidance such as the RREF, HRRR and HiRes-FV3 show
scattered thunderstorms Monday afternoon, yielding around a 20-35%
chance for a shower/t-storm for a given area over the mountains and
adjacent desert slopes. Chances drop to 10-20% Tuesday afternoon and
drop further thereafter, though chances may increase again for late
week if PWAT`s rebound as the ECMWF is forecasting.
Temperatures are still on track to increase Monday through
Wednesday, yielding temperatures generally 8 to 12 degrees above
average - backing off slightly from yesterday`s forecast.
Nevertheless, Major HeatRisk is on track to expand all the way to
coastal areas by late week as highs inland range from 95-107 degrees
F with nighttime low only dropping to the mid-70s (above the very
thin inversion a few-hundred feet above sea level). The low deserts
are consistently expected to see highs of 110-115F Tuesday through
Friday along with Major/Extreme HeatRisk.
While highs in coastal areas mid-late week will mainly remain below
90 degrees F, overnight temperatures will struggle to drop below the
lower 70s, which will especially affect those without access to air
conditioning.
The Heat Advisory remains in effect for inland areas through 10 AM
Tuesday, followed by an Extreme Heat Watch through Friday 8 PM for
the whole region (except for the lower deserts which are already in
an Extreme Heat Warning through Friday evening).
Confidence is low at this point, though both the ECMWF and GFS show
a weakening of the Four Corners ridge, and thus potentially less hot
temperatures, starting next Sunday.
Take breaks in the shade, hydrate and seek A/C when possible!
&&
.AVIATION...
231700Z...Coast...Low clouds and locally dense fog linger along the
immediate coast in San Diego County. Moderate confidence in cigs and
vis at the immediate coast clearing 20Z Sun-00Z Mon. Moderate
confidence in cigs impacting coastal SD between 10-15Z Mon with
bases 200-800ft MSL. Lowered vis 1-3 SM expected with vis less than
1 SM near higher coastal terrain. Low clouds and vis restrictions
may linger along the immediate coast after 15Z Mon.
Otherwise...VFR conditions through the TAF period with FEW-SCT
clouds AOA 20,000ft MSL after 20Z.
&&
.MARINE...
No hazardous marine conditions are expected through Friday.
&&
.BEACHES...
A 4-5 foot southerly swell (from 170 degrees) at 13-15 seconds will
move into the area Wednesday and Thursday, leading to elevated surf
for the south facing beaches of northern San Diego County and Orange
County. Breaking waves of 4 to 6 feet expected, sets up to 8 feet
possible at beaches that face due south. Surf gradually subsides on
Friday.
&&
.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 Tuesday morning through Friday evening
for Apple and Lucerne Valleys-Orange County Coastal Areas-
Orange County Inland Areas-Riverside County Mountains-San
Bernardino County Mountains-San Bernardino and Riverside
County Valleys-The Inland Empire-San Diego County Coastal
Areas-San Diego County Mountains-San Diego County Valleys-
Santa Ana Mountains and Foothills.
Heat Advisory until 10 AM PDT Tuesday 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/BEACHES...CO
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