342
FXUS66 KSGX 022044
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
144 PM PDT Tue Sep 2 2025

.SYNOPSIS...
More widespread showers and thunderstorms will occur across the
coastal foothills to the deserts through Wednesday as greater
monsoonal moisture overspreads the area. Locations west of the
mountains will see warmer and humid weather through Wednesday as
well. A cooling and drying trend will occur by later in the week
over the entire region. There will be minimal chances for monsoon
thunderstorms by the weekend into early next week as temperatures
stay near average.

&&

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

Showers continue over the lower deserts and Mojave deserts this
afternoon. Stronger storms and lightning have dissipated, but
isolated storms are not out of the question for the rest of the
afternoon and early evening as skies partially clear over the
mountains. Most short range models show these showers eventually
dissipating by this evening. There will be better clearing
overnight as this system exits the area. This will lead to a more
typical monsoonal weather pattern as daytime heating and
instability aid in thunderstorms forming over the mountains and
deserts. This will produce another round of locally heavier rain,
gusty winds and cloud to ground lightning. The best chance will be
seen over the mountains, but some storms may form in the valleys
of San Diego County and the eastern half of the Inland Empire.
HREF hourly rain rates show rates surpassing one half inch per
hour by Wednesday afternoon, with rates near one quarter inch
possible the deserts and western valleys. Warmer and more humid
weather will continue across the region, with highs well into the
90s in the western valleys and widespread 70s/80s near the coast
and in the mountains.

Monsoonal moisture will begin to lower by Thursday into Friday as
PWAT values across the deserts lower below 1.5 inches. High
pressure across the western U.S. will also start to weaken. This
will lead for a slow cooling trend into the end of the week. Highs
near 100 today in the Inland Empire will be closer to 90 degrees
by Friday with highs only near 100 across the lower deserts. These
temperatures will be near to 5 degrees below normal and will
continue through the weekend.

Ensemble models hint at a trough of low pressure moving toward the
California coast and an area of high pressure building over the
ocean southwest of San Diego by the weekend into the first half of
next week. The positioning and strength of these features is still
uncertain, but their presence will indicate drier weather for our
region overall as greater onshore flow moves in aloft. The
confidence in the drier forecast is moderate to high, but just how
warm it gets is where we have less confidence. For now, NBM
paints a picture well with keeping highs near average as we move
into the early half of next week.

&&

.AVIATION...
022015Z...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% chance for TSRA at all TAF 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.
SHRA/TSRA chances again Wed limited to mountains, deserts, and
foothills after 03/19Z with cloud/CB based about 10000 ft MSL.

&&

.MARINE...
Isolated rain showers and thunderstorms are possible through this
afternoon. Chances lower significantly after 3 PM today, then end
after about 8 PM. Gusty winds to about 35 knots and low visibility
near any thunderstorm. After about 8 PM tonight, no hazardous marine
conditions are expected through Sunday.

&&

.BEACHES...
Isolated showers and thunderstorms are possible through early
evening, including cloud to ground lightning. Any 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
AVIATION/MARINE/BEACHES...CSP