832
FXUS66 KSGX 070406
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
906 PM PDT Sat Sep 6 2025

.SYNOPSIS...
Mostly clear skies with near average temperatures will occur across
the region this weekend. Monsoonal moisture continues to lower, so
slight chances of weak showers and thunderstorms may occur over the
mountains this weekend as well. Drier weather is expected across all
areas next week. A noticeable cooling trend is expected by the
middle of the week with highs from 5 to 15 degrees below average
with breezier conditions across the deserts and adjacent mountains.
The marine layer will also be deeper next week, contributing to
clouds and fog west of the mountains each night and morning.

&&

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

As of 9 PM, low clouds have been slow to develop along the coast,
with just a small patch currently along the northern San Diego
county coast. Low clouds are expected to develop along much of the
coast overnight. Slight chances (15-20%)of thunderstorms in the
mountains remain in the forecast for Sunday afternoon. High
resolution guidance is indicating rainfall rates of 0.30-0.40 inches
per hour. After Sunday, shower and thunderstorm chances greatly
diminish with dry conditions expected next week.

From previous discussion issued at 2 PM September 6, 2025...

Minor instability and lower monsoonal moisture can be expected
Sunday, so storm chances will be limited to around 15 to 20 percent,
even though a slight increase in PWAT is noted. Whatever falls will
be light across the Riverside/San Diego Co mts into Sunday. A trough
setting up offshore should also help keep shower activity weaker as
well on Sunday if any showers do occur.

The trough off the coast will move closer to the region by Monday,
deepening through Wednesday. This will allow for greater cooling and
onshore flow to overspread the area. Near average temperatures this
weekend will lower to around 5 to 15 degrees below normal.
There is moderate to high confidence in high temperatures staying
below 80 degrees in portions of the Inland Empire, high desert, and
the San Diego Co valleys by Wednesday. Increasing west winds will
also occur across the mountain desert slopes into the deserts by the
middle of the week. NBM mean wind speeds are generally 25-35 MPH,
though higher percentile speeds are closer to 30-45 MPH. This
pattern will favor windy conditions to ramp up across the San
Gorgonio Pass as well, where winds may near 55-60 MPH each day. The
marine layer will also deepen during this time with night and
morning low clouds/fog to push inland for many areas west of the
mountains.

Ensemble models show a weakening of the trough by the end of next
week, but no strong signals on any large features impacting the area
by next weekend. This will help temperatures rise closer to normal
by the end of the week. Drier and calmer weather looks to continue
for the foreseeable future.

&&

.AVIATION...
070315Z...Coast...Initially patchy low clouds will become more
uniform and spread inland up to about 10 miles after 06Z this
evening. Initial bases may be around 800-1200 ft MSL, but are
expected to lower to 600-1000 ft MSL overnight, and vis restrictions
3-6 SM are possible for coastal highlands. Clouds eroding east to
west to beaches 14-17Z. Low clouds will develop again late Sunday,
with slightly lower bases than tonight.

Valleys/Mountains/Deserts...Low chances for a few isolated SHRA and
possibly a thunderstorm 20Z Sun to 01Z Mon, mostly for mountains of
San Diego and southern Riverside counties. CB bases around 10K ft
and any TSRA tops to 35K ft.

&&

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

&&

.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...CSP

NWS Tucson (SGX) Office