Cypress, California Weather Forecast Discussion

901
FXUS66 KSGX 211710
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
1010 AM PDT Sun Sep 21 2025
.SYNOPSIS...
Low clouds cover much of the coastal areas and far western
valleys this morning, with fog along higher coastal terrain.
Subtropical moisture will bring increasing mid and high clouds,
and scattered light showers today, most widespread across the
mountains and in San Diego County. Small chances of showers
continue Monday mainly over the mountains. Chances increase for
Tuesday and could extend into early Wednesday, along with a slight
chance of thunderstorms. Drier weather returns for Thursday and
through the following weekend. Temperatures will be mild this
coming week, with decreasing coastal low clouds.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
This morning, the sounding shows a very shallow marine layer and
a deep moist layer above about 8,000 ft. Satellite imagery shows a
large mass of mid and high clouds moving in from the southwest in
the mean flow aloft between an upper low centered about 315 miles
west of Point Conception and a large high pressure centered over
Mexico with a ridge extending northward into AZ/UT. Scattered
showers and isolated thunderstorms are embedded in the mass of
clouds but the few lightning strikes recorded are about 40 miles
west of San Clemente Island. There remains a chance that those
tstms could reach the SoCal coast later this morning. Low clouds
extend up to 15 miles inland and are beginning to break up under
the shield of higher clouds. Temperatures today will be suppressed
by the cloud cover and light precip, and daytime high temps will
likely be several degrees below seasonal averages in most
areas...including the mtns and deserts.
Numerical models are in good agreement through Tuesday, and the
closed upper low will likely move southward becoming briefly cut-
off on Tuesday about 360 miles southwest of San Diego. This
position will enable the low to advect sub-tropical moisture
northward into SoCal. However, given that there will be very weak
instability, it is more likely that any precip will be stratiform
in nature and in bands extending from southwest to northeast, and
only generally light precip is likely, with amounts of less than
a tenth of an inch for most locations.
For Tuesday through next weekend...
Based on current model consensus, the low will likely move in an
arc - first northeast then southeast - moving directly over SoCal
next Saturday. Most guidance has now reduced the chances for
showers/tstms on Tuesday as the best instability and forcing will
be to the west over the ocean. Rainfall amounts will generally be
less than a tenth of an inch, although, there could be higher
amounts along the west-facing slopes of the foothills, and over
the mountains, where there could be amounts ranging from 0.10-0.25
inches. A storm may also result in locally higher amounts. The
marine layer will also be disrupted by this, and will attempt to
reform and move back inland by much later in the night.Temperatures
will remain on the cooler side, with the cut-off low over the
region, and even slightly below the seasonal average for this time
of year, especially for the inland areas and deserts.
By Wednesday, the position of the upper low will allow for a bit
of a `lull` in terms of the chances of precipitation as the region
becomes more "dry-slotted", and temperatures will also be
slightly warmer as well. The upper low will then begin to
transition slowly towards the southeast as the trough deepens on
Thursday. Since the low will be to the northeast, and
predominantly on the more stable side, there will only be a very
slight chance of showers, and possibly a thunderstorm, on the
backside of this low.
By Friday, there appears to be less agreement among model
solutions, and it will all depend on where the cut-off low decides
to transition which will determine how much of a chance of
showers and thunderstorms there will still be with us on Friday,
and going into Saturday, for the mountains during the afternoon
hours. High temperatures will remain on the cooler side as overall
troughing remains persistent over the region going into the
following weekend, and ensembles also confirm this, with the
relatively cooler and drier conditions locked in through then.
&&
.AVIATION...
211515Z....Coast/Valleys...Low clouds based 400-800ft MSL continue
to clear back towards the coast as mid and high level clouds closer
to 10,000ft MSL move in. VIS remains 2-6SM everywhere with low
clouds, which will continue to improve through 17z.
-SHRA/-RA has already begun to move into the region, with coverage
of -RA increasing after 17z. On and off -RA will continue through
early Monday. Locally lower VIS and CIGs with any SHRA/RA.
Clouds will generally be around 10,000 ft MSL with low marine layer
clouds struggling to develop Sunday night into Monday. Cigs below
3,000ft MSL will extremely patchy, around 20% coverage along coastal
areas with bases 400-800ft MSL, with clearing of any low clouds
likely by 17z.
.Mountains/Deserts...Mid and high level clouds AOA 10,000 ft are
moving into the region from the south. On and off SHRA/-RA expected
for much of the day, with brief lowering of VIS and CIGs with any
shower. Rain chances look to prevail into Monday afternoon.
&&
.MARINE...Rain showers possible for much of the day today and Monday
which could briefly lower visibly. Low chance (5%) for a stray
thunderstorm over the waters today and Monday, with slightly higher
chances on Tuesday (5-10%). Any storm may produce lightning, gusty
and erratic winds, and choppy seas. Otherwise, no additional
hazardous marine conditions are expected through Thursday.
&&
.BEACHES...
Thunderstorm chances return on Tuesday, peak Tuesday afternoon
(10% chance), and may prevail into early Wednesday (5% chance).
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
PUBLIC...PG
AVIATION/MARINE/BEACHES...Zuber

NWS SGX Office Area Forecast Discussion