South Main, California Weather Forecast Discussion

683
FXUS66 KSGX 292056
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
156 PM PDT Mon Sep 29 2025
.SYNOPSIS...
Patchy drizzle possible in the coastal basin overnight with a deeper
marine layer. High temperatures remain well below normal Tuesday.
Gradual warming expected Wednesday through Saturday with a shallower
marine layer. Weak offshore flow may develop Saturday morning.
Cooler and cloudier conditions look to return for early next week.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
A trough of low pressure will approach the west coast and begin to
move inland this afternoon and overnight. This will increase onshore
flow across the area, resulting in more widespread and persistent
cloud coverage this evening and overnight. Some high resolution
guidance is indicating the possibility of patchy drizzle in the
coastal basin, so that has been added to tonight`s forecast.
Additionally there will be a minor uptick in westerly winds over the
mountains and deserts each afternoon and evening today and Tuesday.
In addition to increased clouds and winds, there will be minor
cooling across much of the area into Tuesday.
A few degrees of warming is expected for Wednesday and Thursday as
the low departs to the east, allowing weak high pressure to build in
from the south. Ensemble guidance begins to diverge Friday with the
progression of an upper level trough that is expected to approach
the US West Coast. There remains good consistency with the timing of
the trough, but the amplitude of the trough varies quite a bit.
Currently, around 60% of the ensemble space doesn`t dig as far
south, resulting in less cooling, while the other 40% is more
amplified and therefore cooler on Friday. The spread between the NBM
10th and 90th percentiles on Friday is around 8-10 degrees for
inland areas.
Most guidance shows the trough moving off to the east on Saturday.
This will allow for cooler air to settle into the Great Basin,
setting up surface high pressure, and driving offshore flow across
Southern California. Current guidance indicates the offshore will be
mostly gradient driven, with no upper level support. The CW3E
ensemble currently shows a 20% chance of a weak Santa Ana on
Saturday. This will mainly generate warming conditions west of the
mountains on Saturday. The offshore flow will be brief, as another
low digs through the Pacific Northwest and somewhere into the Great
Basin Sunday and Monday for more cooling and a much deeper marine
layer. Given the inside track of this low, the system will be on the
drier side. Both the GEFS and EPS ensembles are showing at least
light precipitation west of the mountains sometime Mon-Tue, likely
the result of the deep marine layer and stronger onshore flow. For
now precipitation chances are below 15% for Monday.
&&
.AVIATION...
292030Z....Coasts/Valleys...Mostly clear skies throughout the
coastal basin this afternoon. Low clouds based 1500-2200 ft surge
inland in SD County starting 00-03Z, then develop into the rest of
the coastal basin 04-06z. 30-40% chance for -DZ after 11z Tue, with
greatest chances north of SD county. Scatter out 16-18z Tuesday
morning.
Mountains/Deserts...VFR conditions today and tonight. Cumulus based
at 10000 feet MSL mainly over mountains through 01Z Tue. More mid
and high level clouds will move through the region between 05-14z
Tue.
.
&&
.MARINE...
No hazardous marine conditions are expected through Friday.
&&
.BEACHES...
South swell at 4-5 feet with a period of 12-13 seconds will continue
to produce elevated surf and a high rip current risk through
Tuesday. Surf of 4-7 feet with sets 8 feet expected on south facing
beaches. Strong longshore currents will impact all beaches. Surf
will begin to decrease slowly Tuesday with strong rip currents
lingering into Thursday. More information can be found in the Beach
Hazards Statement.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through Tuesday evening for Orange
     County Coastal Areas-San Diego County Coastal Areas.
PZ...None.
&&
$$
PUBLIC...CO
AVIATION/MARINE/BEACHES...Westerink

NWS SGX Office Area Forecast Discussion