951
FXUS66 KSGX 080421
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
921 PM PDT Tue Oct 7 2025

.SYNOPSIS...
Another warm day Wednesday with overnight and morning low clouds.
Moisture from the remnants of Hurricane Priscilla will spread
into the southwest states on Thursday with chances for showers and
thunderstorms for southwestern California for Thursday into
Friday night, with chances lingering in the mountains through
Saturday afternoon. This will be followed by cooling and drying
into early next week with Monday high temperatures 5 to locally 10
degrees below average for inland areas.

&&

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

Evening update:

As of 8:45 PM, a few low clouds have started to develop along
coastal areas. Based on the 00z sounding, the marine layer is
about 2,000 feet deep and the boundary layer inversion is
slightly more pronounced than yesterday`s inversion.

Cloud coverage is expected to increase throughout the night and
bring overcast conditions to all of the coastal basin by early
Wednesday. With weak offshore flow Wednesday morning, clearing is
expected to occur quickly to the coast by around 9-10 AM. High
temperatures should be very similar to today`s.

More high resolution model data is starting to become available,
now converging on timing of a few lines of showers to propagate
region-wide Thursday afternoon with some showers possible as early
as Thursday morning, though with some uncertainty of the
placement of those early showers. While most models suggest that
some of these showers will bring briefly moderate rainfall,
confidence on this occurring is rather low as hi-res models also
show that cloud bases could be at or above 8,000 feet MSL and
rather shallow in depth. If the lowest layer of the atmosphere
remains dry, more likely, lowland areas will only experience
drizzle and light rain Thursday. For Friday, however, there is
better confidence for lower cloud bases and the potential for
heavier showers Friday afternoon into Friday evening.


Previous discussion, as of 2:26 PM:

.SHORT TERM (tonight through Wednesday)...

At the larger scale, as low pressure develops in the Gulf of
Alaska and starts to move down the BC coastline, the smaller low
off the central coast will lift north and open into this larger
wave late tonight through Wednesday morning. Meanwhile, now
Hurricane Priscilla will slowly make its way to the southern tip
of Baja CA by Wednesday morning. These will have little effect on
the weather locally until Thursday.

&&

.LONG TERM (Thursday onwards)...Thursday and Friday, the large
trough in the northeast Pacific will continue to strengthen and
move south. Moisture from Priscilla will filter into south to
southeast CA into AZ as it travels north along the Baja CA
coastline. This will bring the potential for multiple days of
showery precipitation and thunderstorms starting Thursday and
lasting through Friday for most areas, with rain and thunderstorms
possible Saturday as well for the mountains. A few models bring
in the initial wave of showers early Thursday morning, with better
agreement for the late morning into the early evening. This will
also bring the potential for elevated thunderstorms area-wide from
early Thursday afternoon through the evening. National Blend of
Models thunderstorm potential is 15-20% during this period, while
the ECMWF lightning flash density supports the potential for
thunderstorms scattered through the area, including some isolated
flashes along the coast and over the ocean.

More moisture and showers filter in for Friday, though model
solutions of where exactly these move diverge by quite a bit, with
some ensemble members skipping over southwest CA as precipitation
skates south/east of the area. Shower and thunderstorm chances
shift east towards the mountains and deserts over the day Friday
as Priscilla weakens and opens into the large northwest trough.
This continues southeast Saturday, and moisture really starts to
drop off which will limit precipitation chances. There is still
lingering uncertainty with respect to position and amount of
precipitation.

Uncertainty remains on the details, notably event rain totals.
25th percentile event totals show precipitation mostly to our east
and south, with only light amounts locally. 50th percentile has a
few hundredths to 0.10" for south and west San Diego County and
the Inland Empire, with 0.15-0.40" over the mountains (50% chance
of receiving at least that much precipitation). Meanwhile the 75
percentile has 0.20-0.40" across the eastern Inland Empire and
most of San Diego County west of the mountains, and 0.50" to just
over an inch in the mountains (25% chance of receiving at least
that much precipitation). So the reasonable ranges are quite wide.
Chances of receiving an inch or more are 15-20% over the
mountains, and there is a low chance for heavier rain rates on
some of the windward slopes of the mountains where upslope
enhancement of precipitation will occur.

There are lingering 15-20% chances for measurable precipitation
over the mountains through Saturday afternoon as the terrain
barrier provides enough lift to help wring out remaining moisture,
along with a smaller chance for more thunderstorms. Temperatures
will start to drop Saturday.

Sunday will almost certainly be dry as dry, stable air settles in
aloft with the trough continuing to move to the east.
Temperatures continue their downward trend for Sunday into early
next week to 5 to locally 10 degrees below daily averages by
Sunday, potentially even 10 to 15 degrees by Tuesday with another
trough dipping south, but confidence in the latter is currently
low. Some longer range models are bringing enough moisture with
this early week trough to support small chances for rain in the
area for Tuesday, but there`s plenty of uncertainty at this range.

.AVIATION...
080300Z....Coasts/Valleys...Low clouds lingering along the coast
with bases 1500-2200 ft MSL will become BKN/OVC around 04-07Z.
Visibility restrictions of 3-5 SM will be possible at KONT and KSBD
beginning as early as 09Z. Low clouds will reach into portions of
the Inland Empire after 10Z, with a 40% chance of reaching KONT.
Low clouds are expected to scatter out after 16-18Z for inland
locations and through 19/20Z along the coast. Low clouds with bases
around 1500-2000 ft MSL will slowly return along the San Diego coast
beginning around 03Z Thur.

Mountains/Deserts...VFR conditions expected through the TAF period.

&&

.MARINE...
There is a 10-15% chance of thunderstorms Thursday afternoon, with a
5-10% chance Friday afternoon. Lightning, erratic winds, and heavy
rain possible if thunderstorms develop. Occasional northwest wind
gusts near 20 kt are expected Friday and Saturday afternoon and
evening around San Clemente Island.

&&

.BEACHES...

There is a 10-15% chance of thunderstorms at area beaches Thursday
afternoon, with a 5-10% chance Friday afternoon. Lightning, erratic
winds, and heavy rain possible if thunderstorms develop.

&&

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

&&

$$

PUBLIC...Westerink
AVIATION/MARINE/BEACHES...Villafane