848
FXUS66 KSGX 021737
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
1037 AM PDT Tue Sep 2 2025

.SYNOPSIS...
Monsoonal moisture will increase from the southeast this morning
with scattered showers and thunderstorms across much of the area
for today. Thunderstorms would produce cloud-to- ground
lightning, brief heavy downpours, and strong gusty winds to 40 to
50 mph. Chances for mainly afternoon and early evening
thunderstorms, mainly for the mountains and deserts, will
gradually decrease for Wednesday through Friday. Then drier and
gradually cooler for the weekend into early next week.

&&

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

.Morning Update...

Widespread shower and thunderstorm activity has brought over 150
lightning strikes across the region as rain rates rose over one
half inch per hour, highest across the mountains and lower
deserts. Storms have weakened this morning, with mainly light
showers occurring over these regions currently. Hi-res models are
not in good agreement on how thunderstorms develop this afternoon,
leading to a lower confidence forecast. Greater cloud cover
generally acts to inhibit strong storm development, but partial
clearing may lead to isolated storms popping up once again. If
storms do pop up, plenty of instability is present to produce
showers and storms with gusty winds across coastal foothills into
the deserts. Wednesday will see a more typical monsoonal pattern
with mountain and desert storms by the afternoon, some of which
will move into areas west of the mountains with hourly rain rates
near one quarter inch. Monsoon storm chance lowers by Thursday
into the weekend.

.Previous Discussion (512 AM Tuesday)...

.SHORT TERM (Today through Thursday)...
Upper level low pressure will move northwestward across the area
today with monsoonal moisture increasing from the southeast
today. This will bring showers and a chance of thunderstorms over
much of the area today with the greatest chances over the
mountains and high desert for this afternoon.

Radars show showers and thunderstorms extending from around El
Centro to Lake Havasu City at 5 AM. These will begin moving into
the mountains and deserts in San Diego County by 6 AM and into the
Coachella Valley after 6 AM. Brief downpours, cloud-to-ground
lightning, and strong gusty winds are expected as these showers
and thunderstorms move toward the west across San Diego and
Riverside Counties.

The incoming 12Z NKX sounding shows layers with greater saturation
around 550 mb and around 350 to 400 mb. Some of the higher
resolution models show the potential for strong downdraft winds
from high-based showers and thunderstorms. The greater chances for
heavier rainfall are over the mountains where the depth of the dry
air below the mid level cloud bases is less.

The coast and valleys will cool a few to around 5 degrees through
Thursday with lesser changes for the deserts. High temperatures on
Thursday will range from the mid 70s to lower 80s near the coast
to the 90s for the Inland Empire with the upper 90s to 102 for
the lower deserts.

&&

.LONG TERM (Friday through Monday)...
There will be gradual cooling and drying through Monday with
Monday high temperatures around 5 degrees below average for inland
areas. High temperatures on Monday will range from the 70s near
the coast to the mid 80s to lower 90s for the Inland Empire with
the upper 90s to 102 for the lower deserts. There is a chance of
showers and thunderstorms for the mountains and deserts for Friday
afternoon and a slight chance on Saturday afternoon.

&&

.AVIATION...
021730Z...Immediate Coast...Patchy and intermittent coastal low
clouds with isolated CIGs 600-900 feet MSL and vis 0-5SM possible
Wed 11-15Z.

Regionwide...Clouds AOA 10000 feet MSL with SCT -SHRA and isold TSRA
to continue all day with a 20-25% chance for TSRA at all sites
through 00Z, but after 00Z storms gradually migrating
inland/eastwards with decreasing chance for activity region-wide
after 06Z. Gusty and erratic winds, low visibility, and lightning
will accompany any TSRA, along with lower bases 6000-9000 feet MSL.

&&

.MARINE...
SCT -SHRA and isold -TSRA possible through 02Z. Gusty winds to about
35 knots and low visibility near any TSRA. After 02Z, no hazardous
marine conditions are expected through Saturday.

&&

.BEACHES...
Isolated showers and thunderstorms are possible through early
evening, including cloud to ground lightning. Storm activity will
end tonight.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 6 PM PDT this evening for Orange County
     Inland Areas-San Bernardino and Riverside County Valleys-
     The Inland Empire-San Diego County Valleys-Santa Ana
     Mountains and Foothills.

PZ...None.

&&

$$

PUBLIC...APR/17
AVIATION/MARINE/BEACHES...CP