282
FXUS66 KSGX 280412
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
912 PM PDT Wed Aug 27 2025

.SYNOPSIS...
Increasing clouds and moisture from Tropical Storm Juliette will
bring scattered light to locally moderate showers tonight through
Thursday, as well as a 10-15% chance of thunderstorms over the
mountains Thursday afternoon. Warmer and drier weather will occur
Friday into the weekend with less than 10% chances for storm
activity. Monsoonal moisture will slowly return early next week
with a slight chance of afternoon and early evening thunderstorms
for the mountains and deserts.

&&

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

Evening update...
Isolated showers and thunderstorms over the mountains dissipated
earlier this afternoon. The initial band of clouds associated
with Tropical Storm Juliette has made it into Southern California
this evening. There are some weak radar returns moving into far
southeastern San Diego County, but it is likely just picking up
the clouds/virga with no precip being reported at the surface. The
00Z sounding shows most of the moisture above 25000 ft with a
fairly deep dry layer down to 13000 ft and then some residual
monsoon moisture below that. This dry layer should saturate
overnight as deeper moisture from Juliette moves in, producing
light to locally moderate rainfall, with the greatest coverage
over Riverside and San Diego Counties and more isolated showers
northward. High res guidance shows rainfally rates mostly 0.10"/hr
or less, though as the remnant upper low lifts north and into So
Cal, there could be enough dynamics coupled with weak elevated
instability to produce local rates of 0.25-0.50"/hr or more.
Thunderstorm probabilites are fairly low, less than 5% for all
areas tonight, increasing to 5-15% Thursday afternoon with the
highest chances over the mountains.

Otherwise thick cloud cover and the weak low moving through will
bring considerable cooling tomorrow with highs in the upper 70s to
upper 80s in the coastal areas, valleys, and high deserts,
60s-70s in the mountains, and low to mid 90s in the low deserts.

Previous discussion...
Skies will clear out by Thursday night. Friday will see a drying
trend, which will limit the storm chance across the mountains to
near 10 percent. High pressure over northern Mexico will grow and
expand this weekend. This will bring drier, less humid air to the
area with warmer temperatures. This will bring temperatures closer
to near average with highs near 110 across the deserts and 90s
across inland valleys west of the mountains. Cumulus clouds may
build over some of the mountains each afternoon, but the threat
for thunderstorms will be minimal.

The area of high pressure will amplify further over the desert
southwest by next Monday and Tuesday, providing a path for
increased monsoonal moisture to return to our area. This will lead
to increased chances for shower and thunderstorms across the
mountains and deserts with mostly clear skies and near average
temperatures elsewhere. Ensemble cluster models start to have
larger solution spread on the high remaining in place into the
middle of the week, while some others show a weaker trough forming
off the coast, which would bring slightly cooler and drier
weather to our region.


&&

.AVIATION...
280345Z...Very patchy low clouds based 800-1000 ft at the immediate
coast overnight tonight. Remnants from tropical storm Juliette will
slide into the area from the south overnight. High cloud bases AOA
10 kft associated with this moisture will keep conditions mostly
VFR. Occasional -RA/RA for San Diego/Riverside Counties from 11z Thu
to 00z Fri. Gusty outflow winds possible with any afternoon shower
activity.

&&

.MARINE...
Very slim chance (less than 10%) of a thunderstorm over coastal
waters Thursday. If a storm develops, there could be gusty winds
leading to locally rough seas, along with lightning. Otherwise, no
hazardous marine conditions are expected through Sunday.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.

&&

$$

PUBLIC...SS/APR
AVIATION/MARINE...KW

NWS Tucson (SGX) Office