288
FXUS66 KSGX 101549
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
849 AM PDT Sun Aug 10 2025

.SYNOPSIS...
Slight chance of thunderstorms over the San Diego County Mountains
and Santa Rosa Mountains this afternoon and early evening. Hot
temperatures prevail for most locations through Wednesday before a
gradual cooling trend and a deepening marine layer helps return
temperatures to near normal by the end of the week and below normal
by the weekend.

&&

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

.UPDATE...
Low clouds managed to peek into the Inland Empire this morning, but
are quickly clearing back towards the coast where they will hang
just offshore through the afternoon. Confidence is increasing on at
least a thunderstorm or two in the San Diego County Mountains or
Santa Rosa Mountains this afternoon into early evening as soundings
show MLCAPE of around 1200-1800 J/kg for southern San Diego
County Mountains along with PWs >1.2". CAPE and PWs drop
drastically as you go further north, although decent moisture in
the mid levels indicate at least the possibility of storms today
up into the southern portions of the Riverside County Mountains.
Hi-res guidance has started to catch on to this uptick in storm
potential, showing development beginning around 1-2PM. Any storms
will be primarily diurnally-driven, with precipitation ending by 6
or 7PM. After today, precipitation chances fall as a drying trend
sets in and the upper level ridge breaks down by Wednesday with
cooler weather prevailing thereafter.

&&

.PREVIOUS DISCUSSION FROM 249 AM SUNDAY...
Low clouds are a little slower to fill in this morning, but
should spread into the far western valleys and northern Orange
County by sunrise, then clearing back to the coast by late
morning. Further east, mid level clouds are developing over the
Imperial Valley and heading towards our forecast area as outflow
from earlier convection over the Sonoran Desert lifts northwards.
Dew points in the low deserts remain in the low 60s, but no signs
of a true gulf surge yet except in Yuma where winds just picked up
and their dew point jumped up to 76F. High-res guidance does show
moisture increasing across the low deserts later this morning and
mid-level moisture still in place. The moisture in the deserts
will mainly act to suppress high temperatures once again while
making it more humid. Forecast soundings show more favorable
conditions for showers/thunderstorms (15-20% chance) over the
Santa Rosa and central/southern San Diego County mountains this
afternoon, possibly drifting onto the desert mountain slopes. Once
again, the bulk of the convection will be south of the border.
Mid-level moisture begins to decrease on Monday, ending any
thunderstorm chances for the remainder of the week as it only
continues to get drier.

Weaker ridging will be in place over the region today for minor
cooling. The ridge rebuilds from the north Monday and Tuesday for
some warming inland, though areas west of the mountains may not
see much change thanks to a persistent marine layer and afternoon
sea breezes moderating temperatures. Hi-res guidance shows gulf
surges into the lower deserts each night, which will likely limit
daytime temperatures but keep overnight lows elevated. Overall
HeatRisk remains high across the lower deserts with areas of
moderate HeatRisk in the mountains, high desert, and Inland Empire
through Tuesday.

The upper ridge is eventually replaced with long-wave troughing
along the West Coast Thursday into the weekend, though ensembles
are in disagreement with the amplitude of this trough and
therefore how much cooling will occur. Current NBM forecast has
temperatures dropping to around 5-10 degrees below normal by
Saturday.

&&

.AVIATION...
101530Z...Coasts/Valleys...Low clouds based 800-1200 ft MSL will
scatter back to the beaches by 17-18z. Low clouds likely sticking
over nearshore waters and along the beaches this afternoon. Clouds
expected to start moving inland 02-04z Monday with bases 800-1200 ft
MSL, reaching 15 to 20 miles inland overnight.

Mountains/Deserts...VFR conditions continuing through Sunday
evening. Isolated Cu above 15,000ft MSL over mountains of San Diego
County and Riverside County Sunday afternoon 19z-01z with 10-20%
chance of TSRA. Gusty winds near any storms.

&&

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

&&

.BEACHES...
Long period (16-17 second) southwesterly (200-220 degree) swell will
bring elevated surf and high rip current risk from Monday into the
upcoming weekend. Surf of 3 to 6 feet with the highest sets along
south and southwest facing beaches.

&&

.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...Zuber
AVIATION/MARINE/BEACHES...CO