347
FXUS66 KSGX 121906
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
1206 PM PDT Tue May 12 2026

.SYNOPSIS...
Through Wednesday, a weak low pressure system moving into southern
California will deepen the marine layer to around 3000 feet with
night and morning coastal low clouds spreading farther into the
valleys and with slower afternoon clearing for San Diego County
coastal areas. It will be slightly warmer for Thursday and Friday
with the marine layer decreasing in depth, then slightly cooler
for the weekend.

&&

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

.SYNOPSIS...
A cooling trend will continue through Wednesday as weak low
pressure passes through the region. Robust onshore flow will
contribute to a deepening marine layer through tonight along with
breezy conditions in the mountains and deserts today and Wednesday
afternoon. Thereafter, a slight warming trend will commence for
Thursday and Friday. This will be short lived as a weak low
pressure system will bring another cooling trend and deepen the
marine layer for the weekend.

&&

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

A weak upper low just offshore is contributing to strengthening
onshore flow and cooler temperatures today. South to southeast
winds will turn out of the west this evening with gusts 25-45 mph
for the deserts and desert slopes of the mountains both today and
Wednesday afternoon/evening. On the west side of the mountains,
visible satellite indicates that marine layer clouds have held
strong over San Diego and Orange Counties through this morning.
Additionally, temperatures through the coastal basin are 15 to 25
degrees cooler than yesterday at this time. All signs indicate
that our first true "May Gray" day is upon us with coastal areas
expected to stay cloudy through the afternoon. Low clouds will
fill most if not all of the coastal basin tonight with areas of
drizzle expected, especially near the coastline in the early
morning. This will locally create minor visibility reductions. As
the low pressure moves overhead on Wednesday, a weakened inversion
and weaker onshore flow should allow for a mostly sunny afternoon.

Despite the cooling trend, temperatures will still reach the low
100s today across the low deserts. Even Wednesday, which is
expected to be the coolest day, will be around 5-8 degrees above
normal in the deserts with temperatures nearing 100 again in the
Coachella Valley. Meanwhile, temperatures will remain near to
slightly below average in the coastal basin through Wednesday.
Starting Thursday, a weak upper ridge will attempt to nudge into
the region. This will bump temperatures up by a few degrees for
all areas and decrease the depth of the marine layer for both
Thursday and Friday. Thus, temperatures in the low deserts are
expected to reach back into the low 100s Thursday through
Saturday.

Model guidance begins to diverge slightly over the weekend, but
the general consensus is that an upper low pressure system will
pass to the north sometime late Saturday into early Sunday. This
will herald increased onshore flow and a cooling trend resulting
in near average temperatures for all areas by Sunday. A minority
of model solutions produce a few hundredths of an inch of QPF for
coastal areas Sunday into early Monday. However, this likely
reflects the potential for marine layer drizzle and nothing more.
Beyond this weekend, guidance leans toward a warming trend and
slightly above normal temperatures through mid next week.


&&

.AVIATION...
121800Z...Coast/Valleys...BKN-OVC low clouds with bases mostly 1400-
2800 ft MSL will slowly clear inland areas through 20Z, if low
clouds clear the coast it will be intermittent and patchy. Low clouds
will spread inland after 01Z, and rapidly fill the entire coastal
basin to the foothills overnight into Wednesday. Bases will be 1500-
2500 ft MSL overnight. KSNA/KSAN/KONT have 30 percent chance of low
clouds falling below 1000 ft Tue PM-Wed AM. Vis reduced 0-5SM over
higher valley terrain, foothills, and in coastal -DZ most likely 10-
15Z. Slow clearing is expected again Wed AM.

Mountains/Deserts...SCT high clouds and VFR conditions into Wed. SE
winds with gusts 25-35 kt through 00Z Wed becoming NW with local
gusts to 40 kt through 16Z Wed.

&&

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

&&

.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...KW
AVIATION/MARINE...CO

NWS San Diego (SGX) Office