356
FXUS66 KSGX 250449
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
950 PM PDT Sun Aug 24 2025

.SYNOPSIS...
Daily chances for showers and thunderstorms will continue through
the middle of the week as the monsoon weather pattern continues
across the mountains and deserts. Inland valleys may see a storm or
two on Monday, otherwise all areas will remain humid through the
early part of the week. A cooling trend will begin Tuesday and
continue through Friday. A weak trough offshore will help to lower
chances for monsoonal storm activity across the mountains and
deserts by the middle of the week with less humid conditions. The
marine layer will be of similar depth over the next few days with
patchy fog near the coast, pushing further inland by the end of the
week.

&&

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

This evening...The showers and thunderstorms from this afternoon
have dissipated but significant mid-level clouds continue to move
across SoCal from south to north. Patches of low clouds along the
coast will likely be disrupted by the high clouds so low cloud
coverage will likely remain patchy overnight.

From previous discussion...
The monsoonal moisture influx will peak on Monday as PWATs surge
above 1.5 inches across the lower deserts. Atmospheric sounding
profiles show a fairly deep layer of moisture between 300-700mb and
enough instability to have scattered thunderstorms occur across the
mountains and deserts. Hi-res guidance shows the greatest chance (70-
80%) of storms to occur will be from the Mexican border north to Big
Bear, with chances closer to 40-60% across the deserts. Confidence
in how heavy the rainfall will be is moderate as models depict areas
seeing rates near 0.50-0.75 inches per hour by Monday afternoon.
These storms may be accompanied by heavy downpours and minor
flooding, small hail and gusty winds. The flow aloft remains
southerly, so storms will not drift too far west off the mountains,
but adjacent valleys have a smaller chance (15-30%) to see any
rainfall. These same areas will see another chance for storm
activity by Tuesday, but chances are expected to be slightly lower
(50-65%) as moisture decreases with PWATs closer to 1.25" across the
lower deserts. Hourly rain rates therefore, will lower closer to one
half an inch or less; chances also decrease to see rainfall across
the far western valleys.

Areas west of the mountains will remain on the humid side through
Tuesday as monsoonal moisture hangs on. The good news will be a
weak trough off the California coast will begin to form as the
high aloft weakens. This will allow for high temperatures to cool
a few more degrees closer to average. High temperatures will
remain very similar Tuesday through Friday. By Wednesday,
monsoonal moisture and instability will continue to decrease,
leaving around a 15-30% chance of thunderstorms across the
mountains and deserts. The trough`s influence becomes more
pronounced as 500 mb winds, that are now southerly, begin to turn
westerly. This will help to bring in drier air aloft and
stabilize the atmosphere by Thursday into the weekend. Storm
chances across the mountains will be minimal by this time period,
with less humid weather expected for all areas.

Ensemble models show the high across the desert southwest may
restrengthen some by next weekend, which may bring slightly
warmer weather. Looking further out into early next week, a trough
across the Pacific may begin to influence the weather across
California, which would bring near to below average temperatures
and dry weather for our area.

&&

.AVIATION...
250435Z...Coast/Valleys...Patchy low clouds with bases 500-800 ft
will slowly develop along the coast and locally up to 5-10 mi inland
overnight. There is a 50-60% chance of CIGS at KSAN and KCRQ 09-15Z,
and a less than 20% chance at KSNA. Local vis 3-6 SM in BR where
stratus occurs, isolated below 1 SM over higher coastal terrain.
Clouds and vis restrictions clearing 15-18Z. Clouds redeveloping
late Monday night with bases around 600-1000 ft MSL.

Mountains/Deserts...50-70% chance of +SHRA/TSRA over the mountains
and a 35-50% chance over the deserts Monday between 19-02Z. CB bases
near 12 kft and tops to 30 kft. Gusty outflow winds of 35 kt or
more, 1-3 SM vis in +RA, small hail, and lightning are possible.
CB/SHRA dissipating Monday evening.

&&

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

&&

.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...APR/PG
AVIATION/MARINE...SS

NWS Tucson (SGX) Office