252
FXUS66 KSGX 070409
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
909 PM PDT Mon Oct 6 2025

.SYNOPSIS...
High pressure to the southeast will bring gradually warmer days
into Wednesday. The marine layer will decrease in depth with night
and morning low clouds not spreading as far into the valleys by
Wednesday. Thursday into Saturday, moisture from the remnants of
Hurricane Priscilla is expected to spread into the southwestern
California with chances for showers peaking on Friday. Low
pressure from the northwest will bring cooling for next weekend
with high temperatures as much as 5 to 10 degrees below average
for inland areas next Sunday.

&&

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

Evening update:

As of 8:30 PM, patchy low clouds have started to develop along
coastal areas. Based on the 00z sounding, the marine layer is
about 2,500 feet deep and the boundary layer inversion is
noticeably more pronounced than yesterday`s inversion.

Cloud coverage is expected to increase throughout the night and
bring overcast conditions to all of lower SD and Orange counties
by Tuesday morning, with some patchy clouds even reaching into the
Inland Empire. With this inversion and lack of a synoptic mixing
mechanism, there is moderate to high confidence that skies remain
mostly cloudy within 5 miles of the SD county coast all day.
Elsewhere, temperatures remain on track to exceed today`s high
temperatures by a few degrees, which are within a few degrees of
average for early October.


Previous discussion, as of 1:42 PM:

.SHORT TERM...
A gradual warming trend continues through Wednesday as the ridge
continues to nudge in, bringing high temperatures to just about
average by mid-week.

The marine inversion will strengthen and lower slightly
in the next few days, with more coastal low clouds in the late
evening through mid- to late-morning each day through Wednesday
night.

&&

.LONG TERM...
Remnant moisture from now Hurricane Priscilla will start to move
into the area late Wednesday into Thursday morning, drawn in by
southwest flow from a large low pressure system moving down the
OR/northern CA coast. Ensemble model PWAT rises to just above an
inch by the end of the day Thursday, then peaks around 1.5" by
Friday. The average PWAT for this time of year is just under
0.75", so this is well above average. However, remaining model
spread and likely a lack of strong forcing makes for a low
confidence forecast.

What we do have a widespread 15-20% chance for measurable (>=
0.01"), generally showery precipitation across the region as early
as Thursday morning, increasing to 25-35% Thursday into Friday.
Rainfall totals are still in question with model uncertainty
remaining (despite better agreement today). 24 hour total
probabilities of rainfall >= 0.25 are about 20% over southern and
eastern portions of the area and 30% over the mountains and parts
of the deserts by late Friday.

Probability for >=1.00" is about 10%, locally 15%, over the SD,
Riverside, and eastern SBD mountains and parts of the deserts. The
majority of ensemble members show generally light precipitation
for west of the mountains with a few stand out members, but there
is the potential for fairly good upslope flow under the southwest
winds aloft, especially for parts of the SBD mountains. Another
point of uncertainty is the thunderstorm potential. Dynamics
don`t look great, with minimal MUCAPE even at its peak on
Saturday, but enough for a 10-15% chance for thunderstorms most
over the mountains and SD desert.

The northwest trough moves more fully into the region late
Saturday/Sunday, effectively cutting off the moisture source and
also cooling temperatures back to 5-10 degrees below average over
the weekend into early next week.

&&

.AVIATION...
070340Z....Coasts/Valleys...Stratus with bases 1400-1800 ft MSL and
tops to 2500 ft MSL filling in across the coastal areas and western
valleys through 07Z, then spreading into the Inland Empire through
11Z. There is a 60% chance of CIGS at KONT and a 30% chance at KSBD
after 10Z. Areas of vis 3-5 SM in BR/HZ where low clouds move into
the valleys. Clouds/vis restrictions clearing inland 14-17Z and near
the coast 17-20Z. Clearing at KSAN and KCRQ may be limited again,
with a 30% chance of CIGS through the afternoon. Low clouds
redeveloping and spreading back inland after 08/02Z with similar
bases and tops.

Mountains/Deserts...Clear with unrestricted visibility through
Tuesday evening.

&&

.MARINE...
No hazardous marine conditions are expected through Saturday.

&&

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


&&

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

&&

$$

PUBLIC...Westerink
AVIATION/MARINE...SS