913
FXUS66 KSGX 200704
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
1204 AM PDT Sun Sep 20 2026

.SYNOPSIS...
Temperatures remain below normal until Wednesday with a deep
marine layer and perhaps morning drizzle early week. Warmer
weather returns for the end of next week as high pressure builds.

&&

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

The 00z sounding Saturday afternoon shows a well mixed marine
boundary layer, around 2500 feet deep with an inversion up to 5,000
feet and very dry air within and above it. Patchy low clouds are
expected to fill over the lowlands of San Diego and Orange Counties
as well as parts of the Inland Empire through this morning. The
closed upper low continues to approach our region through Monday,
deepening the marine layer to about 4000-5000 feet tonight into
early Monday and significantly improving minimum humidities Monday
afternoon across mountains (12-25% this afternoon to 25-50%
Monday) and deserts (10-15% this afternoon to 18-30% Monday). With
the deepening marine layer, there is a moderate chance for
drizzle in the coastal basin early Monday and early Tuesday.

Monday will also likely be the coolest and breeziest day of the
week as the main trough axis passes through the region. W/SW
winds will be slightly elevated Monday afternoon and evening over
desert slopes, gusting 20-35 mph and higher through the Banning
Pass. Temperatures will likely struggle to reach the 80s across
the Coastal Basin with perhaps a few low-80s in the IE while low
desert temperatures are likely (80% chance) to remain below 100F
both Monday AND Tuesday.

As the closed low departs the region, the longwave background ridge
across the Southern US replaces the low and fills in over SoCal,
immediately spiking the temperatures back to near average for
inland areas for Wednesday, a jump of nearly 8-12F. That
corresponds to highs within a few degrees of 80 at the coast,
upper 80s inland, mid- 90s in the IE and low-100s in the lower
deserts Wednesday through Friday.

At this time, both the ECMWF and GFS are in agreement that a trough
will move through NorCal and the PNW next weekend though it remains
uncertain how much it will have an influence on temperatures in
SoCal.


&&

.AVIATION...
200430Z...Coast/Valleys...Low clouds with cigs ~1500-2200ft MSL will
become more widespread and reach up to 20 miles inland by 12z. There
is a ~30-40% chance for cigs to reach KONT between 12-16z. Cigs
scatter back out 16-18z Sunday, with highest confidence in scatter
out timing for inland locations. It`s possible clearing will be
slower along the coast. Low clouds will return 01-04Z Mon along the
coast with increased chances of cigs filling in the coastal basin by
Mon AM.

Mountains/Deserts...VFR conditions through Sunday with SCT high
clouds AOA 20000 ft MSL in the desert.

&&

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

&&

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

NWS San Diego (SGX) Office