Balboa, California Weather Forecast Discussion

410
FXUS66 KSGX 290957
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
257 AM PDT Mon Sep 29 2025
.SYNOPSIS...
High temperatures remain well below normal with a deep marine
layer through Tuesday. Gradual warming expected Wednesday through
Saturday with a shallower marine layer. Weak offshore flow may
develop Saturday morning. Cooler with a deeper marine layer early
next week.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Marine layer low clouds are very slow to develop this morning with
only patchy coverage in San Diego County, elsewhere skies are
clear. The 00Z HREF seems to have a decent handle on this, keeping
most of the cloud cover over SD County with only 20-30% chances
for areas further north through the morning. Water vapor imagery
shows the short-wave ridge off the So Cal coast and drifting
eastward. This will produce minor warming today, though highs will
still be around 3-7 degrees below normal.
A short-wave trough moving through the mean trough and into CA on
Tuesday will bring minor cooling to the region and a resurgence of
marine layer low clouds for the coastal areas and valleys tonight
into Tuesday morning. This is short lived as an upper level ridge
amplifies across northern Mexico into the Desert Southwest. This
ridge never quite builds directly overhead with the long-wave
trough remaining just off the West Coast, mitigating warming to
just a couple degrees per day and high temperatures remaining a
few degrees below normal.
Ensemble solutions diverge beyond Thursday with the progression of
the upper trough. While timing differences are minimal, the
amplitude of the trough varies quite a bit, with 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.
The trough moves off to the east on Saturday. Cooler air settling
into the Great Basin will set up surface high pressure, driving
offshore flow across So Cal. The CW3E ensemble currently shows a
20% chance of a weak Santa Ana on Saturday. Winds don`t look to be
a major factor at this time, especially with the lack of any upper
level support. This will mainly drive warming west of the
mountains on Saturday. The weather whiplash continues as another
low digs through the Pac NW 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, any moisture associated with
it will be low. 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...
290930Z....Coasts/Valleys...Low clouds with bases 1200-1800 feet MSL
with tops to 2800 feet will continue to fill in San Diego County and
later in Orange and parts of the Inland Empire through 14Z. Local
vis reduced 0-5SM in valleys and higher coastal terrain. Scatter out
expected for most areas 17-19Z, but areas of clouds could linger
intermittently vcnty KSAN through the afternoon (50-60%). Low clouds
with similar bases surge inland starting 00-03Z, likely filling the
coastal basin overnight.
Mountains/Deserts...VFR conditions today and tonight. Cumulus based
at 10000 feet MSL mainly over mountains 19-00Z.
&&
.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...SS
AVIATION/MARINE/BEACHES...MM

NWS SGX Office Area Forecast Discussion