218
FXUS66 KSGX 152037
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
137 PM PDT Mon Sep 15 2025

.SYNOPSIS...
Gradual warming through Tuesday, with gradual cooling for the second
half of the work week. An influx of tropical moisture will bring
chances of showers and thunderstorms for the middle to end of the
week. Highest chances of showers and thunderstorms will be in the
mountains and deserts, with lesser chances west of the mountains.
The marine layer will become shallower early in the week, with the
potential for minimal or no low cloud coverage for the middle to end
of the week.

&&

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

At 1 PM low clouds had mostly cleared from the coast and were
lingering offshore. The marine layer will become shallower into
Tuesday, with low cloud coverage becoming more confined to the coast
and western valleys. For Wednesday onward, there are decreasing
chances of widespread low cloud coverage with patchy to no low
clouds expected.

High temperatures will warm 2 to 5 degrees into Tuesday. For Tuesday
the coast and valleys will be running 5 to 10 degrees above average
for this time of year with the mountains and deserts only 3 to 5
degrees warmer than average. The second half of the work week is
expected to see a gradual cooling trend. The cooling trend will
bring high temperatures back to below average for most locations by
Friday. Latest NBM guidance is showing the potential for warmer
conditions over the weekend.

Mid to upper level moisture from Tropical Storm Mario is expected to
become entrained in an upper level area of low pressure off the
coast of Southern California Tuesday. It looks like there will be
enough moisture and forcing from diurnal heating over the mountains
to generate a few isolated showers and thunderstorms Tuesday
afternoon. High resolution guidance from the HRRR has hourly
rainfall rates 0.50-0.75 inches per hour, with most of the coverage
on the mountain ridges and desert slopes. By Wednesday, there is
expected to be a further increase in moisture and the environment is
expected to become more unstable. Latest guidance has the bulk of
the widespread rainfall occurring Wednesday evening into Thursday
afternoon, with the potential for showers and thunderstorms from the
coastal waters to the deserts. By Thursday afternoon, chances for
showers and thunderstorms decrease for places west of the mountains
but remain 60-70% for the mountains and deserts. Shower and
thunderstorm chances lessen Thursday night into Friday, with the
best chances of showers and thunderstorms on Friday afternoon in the
mountains and deserts. The tropical moisture will slowly decrease
through Sunday, but it looks like there will be enough remaining in
the atmosphere to bring afternoon showers and thunderstorms to the
mountains, potentially into the deserts both Saturday and Sunday.


&&

.AVIATION...
152000Z...Coast/Western Valleys...Low clouds have cleared from
coastal areas and are lingering offshore. Low clouds will return to
coastal areas after 03Z Tue. Bases will be lower tonight with
patchier and less uniform coverage. Cigs will be 700-1000 feet, vis
3-5SM confined to coastal areas. Currently there is low confidence
in persistent cigs through the overnight ours. Any lingering low
clouds are expected to clear 15-17Z Tue.

Inland Valleys/Mountains/Deserts...VFR conditions through early
Tuesday. Thunderstorms possible over the mtns 21Z Tue-02Z Wed. CB
bases AOA 10000 ft MSL. Lightning and gusty winds expected where
thunderstorms develop.

&&

.MARINE... There is a slight chance of thunderstorms Wednesday night
through Friday morning. Any storms that develop could briefly
produce gusty winds, choppy seas, and lightning. Otherwise, no
hazardous marine conditions are expected.

&&

.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...CO
AVIATION/MARINE...Westerink/CO