917
FXUS66 KSGX 060311
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
811 PM PDT Sun Oct 5 2025

.SYNOPSIS...
Below normal temperatures through Monday, with a gradual warming
trend into the latter part of the week. Areas of night and morning
low clouds and fog will continue along the coasts and parts of
the valleys through midweek. Mid and high level tropical moisture
moving into the region will bring a slight chance of showers late
Thursday through Saturday.

&&

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

Evening update:

As of 8:00 PM, a few patchy clouds have developed along coastal
areas. The closed low referenced in the previous discussion is
detaching from the parent trough and now centered off the coast of
central California. The parent trough is lifting and moving
eastward meaning Southern California currently finds itself
between these two weak upper lows.

The 00z sounding shows a significantly more impressive low level
inversion from yesterday`s sounding, giving increased confidence
for much greater coverage in low clouds tonight, first into Orange
and San Diego County lowlands and eventually into the Inland
Empire during the early morning hours of Monday.


Previous discussion, as of 1:42 PM:

.SHORT TERM...

Zooming out, a large scale positively tilted trough is over much
of the north-central and western U.S. A shortwave can be seen
developing on the west side of the trough off the north-central
California coast currently. This will develop into a little closed
low late today into Monday morning as it moves down to the south-
central California coast, and the weak ridge over the southern
U.S. moves to cover Southern California. This will result in a
gradual warm up for areas inland from the immediate coast through
Tuesday, starting with inland high temperatures today that will be
2-5 degrees warmer than yesterday`s. Temperatures will still be a
couple of degrees below the daily average today, despite this
mild warm up. A few degrees of warming each day through Tuesday
will bring temperatures closer to normal.

The inversion will strengthen tonight, leading to more widespread
low cloud coverage overnight. Clouds that develop this evening
will still initially be quite patchy, and could remain patchy to a
certain extent overnight, but will be much more uniform than
previous days and make it further inland, even possibly into parts
of the western and southern Inland Empire. It will also be slow to
clear in the mornings, lingering along the coast possibly into the
early afternoon. Similar story through mid-week.

The low lifts north and opens up late Tuesday into early
Wednesday, but result in little change to the local area. A very
large low pressure system will drop south from the Gulf of Alaska
mid- to late-week, though models have come to more of a consensus
that this impacts from this will remain well to our
north/northwest through early Thursday.

&&

.LONG TERM...
The potential for some more interesting weather has increased a
bit for late next week into the first half of the weekend, though
confidence in the details is still low as the models struggle to
resolve them. Moisture advected from now Tropical Storm Priscilla
will enter the area starting Thursday, and ensemble mean
precipitable water peaks around 1.25-1.5" Friday. Meanwhile the
large low pressure system will continue southwards, though the
main impacts and lift provided from this system looks to stay to
our north.

As a result, showers are possible for all areas Thursday through
Saturday, with chances peaking Friday at 15-30%. Just over half
of global ensemble members are now showing precipitation for San
Diego County, with that number decreasing a bit for areas further
north. Most of the members are indicating light precipitation,
with the majority of the moisture above 700 mb, and the ensemble
mean is around 0.20-0.40". A few outlier solutions are very wet,
as they are showing better dynamics provided from the low
traveling a little further south. This latter solution would also
lead to better conditions for thunderstorms. Currently the
National Blend of Models is indicating a 5-10% chance for
thunderstorms, locally to 15% in some of the mountains.

The low opens around Saturday and then pushes eastward late
Saturday into Sunday, taking the moisture with it and ending
precipitation chances likely by Sunday morning. This will also
lead to cooling over the weekend to below normal temperatures.

&&

.AVIATION...
060300Z....Coasts/Valleys...Low clouds near 1500-2000 ft MSL will
continue to fill into areas near the coast this evening. A coastal
eddy will help to push low clouds to many inland valleys overnight,
including portions of the Inland Empire. There is a 75% chance of
BKN cigs reaching KONT by 10Z Mon and a 40% chance of low clouds
reaching KSBD by 12Z Mon. FEW-SCT conditions will return 17-19Z Mon
for inland areas. Confidence increasing in BKN cigs lingering for
VCTY KSAN/KCRQ into Monday afternoon, less so in Orange County. Low
clouds with similar bases moving into the coast and western valleys
after 02Z Tues.

Mountains/Deserts...VFR conditions will continue through Mon.

&&

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

&&

.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/CSP
AVIATION/MARINE...APR

NWS Tucson (SGX) Office