922
FXUS66 KSGX 130417
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
917 PM PDT Sun Oct 12 2025

.SYNOPSIS...
A low pressure system moving southward along the West Coast will
bring stronger onshore winds Monday into Tuesday night, along with
widespread precipitation from the coast to the mountains Monday
night into Tuesday night. Gradual warming and drying with periods
of weak offshore flow Wednesday through Friday. For next weekend
the warming continues inland while marine layer clouds and fog
return to the coastal areas.

&&

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

Evening update...
Water vapor imagery shows an upper level low along the Washington
coast with a trough axis extending south off the coast of
California. The upper low will drop south tonight, and combined
with a strengthening coastal eddy, will help deepen the marine
layer. Patchy low clouds have formed over the San Diego County
coastal areas and valleys, but should become widespread and fill
in across much of the coastal basin overnight. The approaching
trough will also usher in cooler weather on Monday as high
temperatures drop to 5-15 degrees below normal. No changes to the
forecast this evening, though it should be noted that as more
high-res guidance comes in, confidence is increasing in higher
rainfall rates, possibly 0.50 inch/hour or more, occurring just
ahead of the cold front on Tuesday. This increases the risk of
minor urban flooding and flash flooding/debris flows below the
recently burned areas.

Previous discussion...
By late Monday, the tightening gradient ahead of the approaching
shortwave will lead to elevated to strong wind gusts for the
mountains and deserts. Winds peaking late Monday night with
widespread gusts 30-40 mph and exceeding 55 mph for the wind-
prone passes and slopes. This system will also bring colder air,
and chances for showers and high-elevation snow. Tuesday will
likely be the coldest day with daytime temperatures as much as
10-20 degrees below normal in the inland valleys, mountains and
deserts. Precipitation will begin Monday night into early Tuesday
morning, starting in the northern and western areas (vicinity LA
basin) and spreading south and east through the day on Tuesday
before ending Tuesday night. Rainfall guidance has trended upward
slightly due to the track of the low shifting slightly west which
allows for more marine influence. Rainfall rates may exceed 0.25"
per hour for the northwestern coastal basin in OC and the western
Inland Empire. Higher rates possible for coastal slopes of the
Santa Anas and San Bernardino County Mountains. Rainfall amounts
will range from 1 to 2 inches along the coastal slopes of the San
Bernardino County Mountains to almost nothing in the lower
deserts. Generally higher amounts expected in the northern and
western areas with 0.25-0.75" for lower elevations of OC and the
Inland Empire. Generally less than 0.25" in the vicinity of San
Diego. Snow levels will remain generally above 7000 feet with
minor accumulations above resort levels. Big Bear Lake may see a
dusting.

Much more benign weather expected from Wednesday onward with a
gradual return to seasonably cool temperatures by late week. A
weak offshore surface pressure gradient may inhibit marine layer
clouds from reclaiming the coastal basin for a few days. By the
weekend, a weak ridge should be in place along with continued
seasonably cool temperatures. From there, solutions diverge
notably but there is some indication that another upper low
pressure system may affect the west coast early next week.


&&

.AVIATION...
130300Z....Coasts/Valleys...Low clouds based near 1500-2000 ft MSL
have started to form over coastal areas and will spread into Orange
County and southern Inland Empire after 08Z, and as far inland as
KONT and KSBD around 14-15Z. CIGs will rise overnight through Mon
morning across the region between 2000-4000 ft MSL. Inland areas
will scatter, but there is increasing confidence in coastal TAF
sites being BKN all day Monday. Chances for VCSH will begin to
increase between 00-06Z Tues from the northwest to the southeast.

Mountains/Deserts...VFR conditions expected through the TAF period.
Gusty W/SW winds along desert facing slopes of the mountains into
the deserts after 18Z Mon. Wind gusts 25-40 kts leading to MOD UDDFS.

&&

.MARINE...
No hazardous marine conditions are expected through Monday, though
winds will be breezier than average out of the southwest Monday
afternoon. A weather system approaches the area Tuesday, increasing
winds out of the south to southwest. Winds of 20-25 knots and choppy
seas are anticipated for all areas Tuesday morning through the
evening.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from 11 AM to 11 PM PDT Monday for Apple and
     Lucerne Valleys-San Gorgonio Pass near Banning.

PZ...None.

&&

$$

PUBLIC...SS/KW
AVIATION/MARINE...Villafane