843
FXUS66 KSGX 171648
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
848 AM PST Mon Nov 17 2025

.SYNOPSIS...
Isolated light showers will continue this morning along and west
of the mountains. A weaker Pacific storm will move through the
area this afternoon through Tuesday evening, bringing widespread
rain and mountain snowfall for areas above 5,000 feet. Isolated
showers continue into Wednesday with moisture wrapping around the
north side of the low pressure system. A third system may bring
additional by late Thursday or Friday, though details with this
system still remain uncertain.

&&

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

.Morning Update...

Clouds and sun are moving over the region after a beautiful
sunrise. The next incoming weather system to impact our area is
currently near the Central Coast, giving showers from Santa
Barbara to San Luis Obispo up to the Bay Area. Hi-res models show
this line of showers that is currently near Ventura/Santa Barbara
to move from west to east starting by the mid to late afternoon
hours across the LA Basin, then moving into parts of San Diego
County by this evening after 6 PM, where evening commutes may be
impacted. Tuesday still looks to be the coldest day of the week
with highs in the 50s/60s for lower elevations and 30s/40s for
mountain areas. The forecast remains on track for this system to
rotate over the region, leaving the continued chance of rain and
high elevation snow for many through Tuesday into early Wednesday.


.Previous Discussion (238 AM Monday)...

An incoming low pressure system will track south along the coast
today, slowly moving east across So Cal Tuesday and Wednesday. The
main band of precipitation associated with the cold front moves
through this afternoon and evening, bringing another round of
widespread precipitation and a slight (10-15%) chance of
thunderstorms with it. Brief, heavy rain with rates upwards of
0.50"/hr are possible within a narrow band right along the cold
front. Isolated to scattered showers will follow the front late
tonight all the way into early Wednesday. Ensembles are showing at
least weak instability (mean CAPE of around 100 J/kg) for the
mountains westward Tuesday afternoon, for another slight (10%)
chance of thunderstorms. Depending on how the low tracks and how
slowly it moves off to the east, we could remain in wrap around
moisture on the north and west sides of the low through the day
Wednesday. If it tracks slowly enough for moisture to remain into
the afternoon, we could see another round of showers as daytime
heating/destabilization occur, predominantly over the mountains
and deserts.

Storm total precipitation with this low are forecast to be around
0.50-0.75" for the coasts to the mountains, with amounts of 1-1.6"
on the south/southwest facing coastal slopes, 0.10-0.30" in the
deserts, and less than 0.10" in the deserts. Desert amounts could
end up being higher should the wrap around showers materializes.
Snow levels will be much lower with this system and have trended
lower since yesterday, now bottoming out at around 4500-5000 ft
across the San Bernardino Mountains and 5000-5500 ft in
Riverside/San Diego Counties Tuesday morning. This will be in the
colder air behind the front after the majority of the
precipitation occurs though, so do not expect much accumulation at
these elevations (less than 0.5" of snow). Snow levels will be
closer to 6500-7000 ft in the main precipitation band. Snow
totals for 5500-6500 ft will be near around1", 2-4" between
6500-7000 ft, and 4-8" above 7000 ft. Again, this amounts could
end up increasing if the wrap around showers occur, especially for
the northern slopes of the San Bernardino Mountains.

A brief break in precipitation occurs Wednesday night through
Thursday afternoon. Ensembles are starting to come into better
agreement with the track of the next system, though consequential
differences remain. They have trended away from the inside slider
track, which now only accounts for about 10% of the ensemble
space, meaning the potential for this storm to miss us with that
track has decreased. Around 20% of the members, the majority from
the GEFS, follow a track close to the deterministic GFS, swinging
the upper low further west and south before moving inland across
Northern Baja. The trajectory of the short waves around this low
will determine where the heavier precipitation occurs. A further
west and south track would favor San Diego County with lower
precipitation amounts to the north. A slight westward but less
southerly track would favor the coastal areas, and a more direct
route (much like the early week system) would more evenly
distribute precipitation across the region. The range of storm
total precipitation remains massive - anywhere from zero to over
an inch for the coasts to the mountains.

Once this upper level low departs (sometime Sunday or Monday),
weak upper level ridging will build in from the west bringing
drier weather and high temperatures returning to normal. Otherwise
highs will remain well below normal for the week, at times as much
as 15-20 degrees below normal.

&&

.AVIATION...
171630Z...FEW-SCT low clouds based 2-6 kft will linger through the
coastal basin through the morning. A frontal precipitation band
arrives from the northwest starting in Orange County around 01-02Z
Tue, reaching San Diego by 05-06Z, and pushing over the mountains
and into the low deserts by 09-10Z. Expect a few hours of cigs 1000-
2500 feet MSL and vis 1-5SM through the coastal basin with the
passage of this band. Cigs/vis lifting and/or scattering out with
generally VFR conditions, thereafter. Higher terrain obscured in
FG/RA during the frontal passage and through the overnight hours.
SCT -SHRA/SHRA begins to develop 12-18Z Tue, reintroducing the
threat for intermittent MVFR cigs/vis through the coastal basin.

&&

.MARINE...
A cold front will arrive late this afternoon with a distinct wind
shift from southerly to westerly. The westerly winds behind the
front will gust 20-25 knots at times. Check the Small Craft Advisory
for details.

There is a slight chance of thunderstorms this afternoon
and evening, and again Tuesday afternoon. Any thunderstorm could
produce lightning, gusty erratic winds, choppy seas, and/or a
waterspout. No hazardous marine conditions are expected Tuesday
night through Thursday, but the next storm system has the potential
to bring hazardous winds and seas Thursday night and Friday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 4 PM this afternoon to 2 AM PST
     Tuesday for Coastal Waters from San Mateo Point to the
     Mexican Border and out to 10 nm-Waters from San Mateo Point
     to the Mexican Border Extending 10 to 60 nm out including
     San Clemente Island.


&&

$$

UPDATE...APR
PUBLIC...SS
AVIATION/MARINE...KW