883
FXUS66 KSGX 170929
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
229 AM PDT Sat May 17 2025

.SYNOPSIS...
Cooler conditions with increased cloud cover and stronger, gusty
westerly winds expected over the weekend. Low clouds will fill in
much of the coastal basin each night and morning. There are
chances of light rain and drizzle west of the mountains this
morning and tonight into Sunday morning. Warmer conditions with a
shallower marine layer is expected for next week. Periods of
locally gusty offshore winds are expected Monday morning through
Monday afternoon.

&&

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

This morning...A closed upper low over northern Mexico is ejecting
to the northeast from the base of a large-scale trough over the
Desert Southwest. This is in response to a shortwave trough moving
southeast in the mean northwest flow over the west coast. This has
resulted in the marine layer now becoming about 3000 feet deep
with low clouds covering most of the region west of the mountains.
There is a good chance that the saturated layer becomes thick
enough to produce patchy drizzle west of the mtns this morning.

As that shortwave continues to move southeast, it becomes a
closed upper low over the Great Basin by Tonight. This system will
bring stronger westerly winds to SoCal today through tonight. The
winds have begun to strengthen and the wind-prone locations in
the mtn passes have begun to report wind gusts of 35-50 mph. Winds
will peak this afternoon/evening with gusts of 45-55
mph...locally up to 65 mph in the windiest locations. The gusty
winds could bring areas of blowing dust and sand in the deserts,
reducing visibility at times. This reinforcing shortwave could
produce enough dynamic forcing to convect what little moisture
there is, and high-resolution models are showing small chances
for Isold-SCT light showers from late this morning through
tonight. Rainfall totals are unlikely to exceed 0.10 inch from
the mtn slopes to the coast. Today will be a cool day, with
daytime high temperatures a few degrees below normal in the
coastal areas and deserts to as much as 15 degrees below normal in
the inland valleys.

Dry with a warming trend beginning on Sunday as low pressure
moves eastward into the Rockies and weak high pressure builds over
the west coast. A surface high moving into the Great Basin will
bring periods of weak offshore flow on Monday, with locally gusty
northeast to east winds. Current guidance shows the offshore winds
peaking late Monday morning with local wind gusts of 35 to 40 mph
on the coastal slopes of the San Bernardino Mtns, in the northern
parts of the IE and in the Santa An Mtns. The offshore winds will
weaken on Monday evening.

Under the weak high pressure aloft, temperatures will continue to
rise through midweek and Wed and Thu are likely to be the warmest
days with daytime high temps reaching the mid to upper 90s in the
IE on both those days. The marine layer will maintain less of a
presence with day-to-day variations on the amount of low
clouds/fog during the nights and mornings but daytime temperatures
will reach the mid 70s near the coast.

Temperatures will again trend lower for next weekend as a low
pressure trough approaches from the northwest but there isn`t much
confidence in the details of the forecast due to the spread among
model solutions.

&&

.AVIATION...
170900Z...Coast/Valleys...Satellite shows the marine layer has
managed to push all the way up to the mountains with bases ranging
from 1500-2300ft MSL and tops to 3000ft. Patchy drizzle is possible
through 18Z, especially for inland valleys, which could locally
lower VIS to 4-6SM and CIGs to 1000-1500ft MSL, but
significant/prolonged impacts unlikely. Partial clearing will occur
for eastern valleys after 18Z, but most other areas will remain BKN-
OVC all day, though CIGs rise to 2000-3000ft MSL and prevail into
Sunday morning. More scattered light showers/drizzle expected after
00Z Sunday.

Mountains/Deserts...SCT high clouds prevail. West to southwest gusts
25-40kts over the desert foothills and through passes will become
more widespread through the deserts and strengthen to 35-55kts after
17Z, producing strong up/downdrafts in the lee of mountains such as
vcnty KPSP. BLDU likely 20Z Saturday through 08Z Sunday, primarily
in the deserts and Coachella Valley, where VIS may fall below 3SM at
times.

&&

.MARINE...
Onshore winds gusting near 20kts near San Clemente Island late this
afternoon into early Sunday may lead to some choppy seas in the
outer waters. Otherwise, no hazardous marine conditions expected
through Wednesday.

&&

.BEACHES...
Elevated surf will impact beaches Sunday and early Monday. Expected
surf of 4-6 feet would produce a high rip current risk.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from noon today to 2 AM PDT Sunday 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...None.

&&

$$

PUBLIC...PG
AVIATION/MARINE/BEACHES...Zuber