388
FXUS66 KSGX 101713 CCA
AFDSGX

Area Forecast Discussion...CORRECTED
National Weather Service San Diego CA
1013 AM PDT Fri Oct 10 2025

.SYNOPSIS...
A low pressure system off the West Coast will continue to draw
moisture from Tropical Storm Priscilla northward into the area
through Saturday morning, with chances for showers and
thunderstorms at times. Cooler with drying and a return of the
marine layer early next week. For Tuesday and Wednesday of next
week, a low pressure system moving southward along the West Coast
will bring a chance of showers along with stronger westerly winds.

&&

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

Update: Latest water vapor imagery reveals that the main moisture
plume streaming northward from the area of low pressure associated
with the decaying remnants of Priscilla is remaining confined to the
southeast of the CWA at this time. There is will some upper level
difluence, along with weak instability that is providing a few
showers over the region this morning. This will continue throughout
the day as the low pressure advances slightly northward, with
bands possibly developing over the coastal and inland areas.
However, given the nature of our area being somewhat "dry-slotted"
by being located in between the longwave trough upstream to the
northwest, and the weakening tropical system to the south, there
will likely only amount to very sparse development, with some
areas getting in on the precipitation, while most other areas
remain dry. As we progress into the afternoon, the mid levels will
begin to destabilize, and orographic lifting will help to aid in
the development of a few thunderstorms over the mountains. If
these storms become nearly stationary, or train over the same
area, it could become problematic, as PWATs are still over 100
percent. Although, given that MUCAPE is just over 600 J/kg, based
off of the KNKX sounding this morning, as well as there being some
CIN (convective inhibition) I have growing confidence that
impacts will be more sparse and localized. Moreover, the main
source of moisture may remain mostly confined to just the
southeastern portion the San Diego County. Shower/storms that do
develop should have a northeastern movement to them due to mid-
level flow being out of the southwest, so for instance, if a storm
does form over Mt. San Jacinto, it may be impactful for Palm
Springs. Again, this will all depend on where the "splitting"
(difluence) of the upper levels occurs, which will determine where
the convection develops.

In terms of tomorrow and beyond, most of any remaining shower/storm
should depart the CWA by later this evening, with clearing skies
going into tomorrow morning. There still exists the very slight
chance of a thunderstorm over the mountains during the afternoon
hours tomorrow, although it is more likely that conditions will be
dry for all, and winds will be increasing out of the west with more
influence from the troughing upstream beginning to take shape.
Deterministic models have been resolving area of low pressure that
deepens during the mid part of next week, and may drying us a
much better chance of measurable precip, especially for the
coastal/inland areas, as well as much colder temperatures.

(Previous discussion submitted at 245 AM):

This morning, a band of light showers extends from the coastal
waters near San Clemente island to the high deserts northeast of
Big Bear. The band as a whole is slowly drifting northward even as
the elements move to the northeast in the mean flow around the
base of a trough extending from a low pressure system centered
off the Oregon coast. So far, rainfall amounts have been light,
ranging from a trace to about two tenths inch in the last 12
hours. While the bulk of the moisture from what is still Tropical
Storm Priscilla remains to our east and south, there is no
shortage of moisture over SoCal, with about 1.4 inches of
precipitable moisture. What we seem to lack is a deep, unstable
layer and a mechanism for forcing deep convection. Moisture from
Priscilla will continue to be drawn into SoCal through late
tonight or early Saturday morning, continuing the chances for
showers and tstms. Chances for tstms with locally heavier rainfall
increase over the mtns and deserts late today as Priscilla`s
upper level circulation is drawn into the mean southwesterly flow
becoming an open wave by this afternoon and all but vanishing in
the circulation around the low to the northwest by Sat morning.
Overall, precipitation is not expected to be heavy but locally
heavy rainfall in tstms can`t be ruled out due to the amount of
available moisture.

Fair and cool weather is expected from late Sat through Monday
under cyclonic flow aloft. Onshore flow will strengthen late Sat
into Sun morning as the low moves inland to the north. Winds will
peak Sat evening with localized gusts of up to 50 mph in the
favored mtn passes and adjacent desert areas. The marine layer low
clouds and fog could make a return as soon as Sat morning but more
likely for Sunday and Monday mornings.

For next Tue and Wed...Model solutions begin to diverge on Monday
as a reinforcing shortwave trough moves southward out of western
Canada into the mean trough over the western US. Beyond Monday,
forecast details are uncertain due to significant spread in the
model solutions with respect to the timing and placement of the
low pressure system as it forms a closed upper low near WA/OR on
Monday then moves southward along the coast, reaching SoCal on
Wed. Depending on which solution verifies best, we could be cold,
windy and wet for Tue-Wed or we could be cold, windy and not so
wet. There is a small chance for a dusting of snow on Tue in the
San Bernardino Mtns above 7,500 ft but it`s not something I would
plan on at this point.

The low/trough moves inland toward the end of next week and fair
weather will likely return but the timing remains uncertain.

&&

.AVIATION...
101515Z....BKN clouds based 8000-12000 feet MSL with ISO -SHRA
regionwide today and tonight, and ISO-SCT SHRA/TSRA inland 18-04Z.
Best chance of rain will be across the mountains and the deserts.
Any TSRA could lower cloud bases to 5000 feet MSL briefly, and could
bring gusty winds and reduced vis in +RA. Decreasing clouds and
-SHRA overnight into Saturday morning. Low to moderate confidence on
any BKN cigs based around 1000-2000 feet MSL developing 09-17Z
Saturday near the coast; highest confidence near VCTY KSAN.
Otherwise, drier and clearer on Saturday for the region.

&&

.MARINE...
Northwest wind gusts occasionally exceeding 20 knots around San
Clemente Island during the afternoons and evenings today and
Saturday. No hazardous marine conditions are expected today through
Tuesday.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.

&&

$$

UPDATE...Stewey
PUBLIC...PG
AVIATION/MARINE...APR