312
FXUS66 KSGX 120950
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
250 AM PDT Mon May 12 2025

.SYNOPSIS...
A significant cooling trend will take place today and Tuesday.
At the same time, westerly winds will be strong in the mountains
and deserts. There is a slight chance of very light showers along
with patchy drizzle mainly in foothills tonight into Tuesday.
For Wednesday through at least Friday, look for warmer seasonal
weather with a shallower marine layer. Another trough will bring
cooler, breezier and cloudier weather next weekend.

&&

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

Low clouds and fog have made decent progress filling in coastal
areas and extending into western valleys so far this morning.
Winds through mountain passes and on desert slopes are increasing
with some gusts in the mountain passes exceeding 40 mph. These
winds will continue rather strong through areas of the mountains
and deserts through Tuesday night. Strongest gusts through passes
and on desert slopes will reach or exceed 55 mph. Hang on tight
because we`re on a temperature roller coaster. We reached the top
this weekend and today we`ll pick up speed plummeting downward, a
stark contrast to the weekend`s record heat. Highs west of the
mountains will be in the 60s, maybe touching 70, which is roughly
10-15 degrees below average, and nearly 35 degrees down from
Saturday in the valleys. The marine layer will deepen
considerably tonight and Tuesday, leading to patchy drizzle in the
coastal basin and even a slight chance of showers most likely in
the foothills. Rain amounts will be close to zero, but isolated
spots in the foothills could wring out up to 0.20 inch. These
rather big changes in our weather come courtesy of a West Coast
trough of low pressure diving down the coast and amplifying
through the West tonight and Tuesday. The trough weakens Wednesday
and pulls out Thursday, but shortwave troughs continue to
maintain the longwave trough pattern. This will maintain a
moderate depth marine layer and temperatures close to or slightly
below normal. A stronger trough appears to arrive Saturday. This
will deepen the marine layer further and cool the weather for the
weekend. Sunday`s high temperatures could be 10 degrees below
average, almost as cool at Tuesday`s, and quite a contrast from
the previous weekend`s. Look for winds in the mountains and
deserts to crank up again, too. A weaker leftover trough hangs
around early next week.

&&

.AVIATION...
110915Z...Coast/Valleys...Low clouds based at 1200-1600 ft MSL with
tops to 1900 ft present along the coast and have moved about 20
miles inland. Clouds aren`t expected to move into most of the Inland
Empire tongiht, but there is a 20% chance that KONT could see cigs
11-17Z this morning. Low clouds scatter to the beaches 16-18Z, but
could linger in patches along the immediate coast through 20Z. Low
clouds based 2000-3000 ft MSL will reform after 01Z Tue, filling
into the coastal basin overnight.

.Mountains/Deserts...High clouds AOA 20000ft but otherwise clear
with VFR conditions through tonight. Localized elevated westerly
wind gusts 30-40 kt will continue along desert slopes and through
mountain passes with mod up/downdrafts early this morning, before
becoming more widespread through the mtns/deserts after 15Z with
gusts up to 55 kt along desert slopes and through mountain passes.
Strong up/downdrafts possible. BLDU in windier corridors, primarily
in the deserts.

&&

.MARINE...
Strong west-northwest winds will continue through Tuesday, with
sustained winds of 15 to 20 kt and gusts to 25 kt across the outer
coastal waters leading to hazardous conditions for small craft,
strongest winds near San Clemente Island. A Small Craft Advisory
remains in effect through late Tuesday night. Winds briefly diminish
late Monday through Tuesday morning, but will strengthen again
Tuesday afternoon and evening. Winds taper off by Wednesday morning.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory until 5 AM PDT Wednesday for Apple and Lucerne
     Valleys-Riverside County Mountains-San Bernardino County
     Mountains-San Diego County Deserts-San Diego County
     Mountains-San Gorgonio Pass near Banning.

PZ...Small Craft Advisory until 11 PM PDT Tuesday for Waters from San
     Mateo Point to the Mexican Border Extending 10 to 60 nm out
     including San Clemente Island.


&&

$$

PUBLIC...MM
AVIATION/MARINE...CSP