156
FXUS66 KSGX 190032
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
532 PM PDT Sun Oct 18 2026

.SYNOPSIS...
The coastal basin will continue to cool a few degrees early this
week while mountain and desert regions warm slightly. Patchy
coastal fog is possible Monday morning and more likely early
Tuesday. Further cooling expected across the entire region
starting Tuesday as a low- pressure system begins to move in from
the northwest. This will bring widespread light to moderate rain
to the region Wednesday into Thursday along with elevated
southwest winds for the mountains and deserts as well as
thunderstorms for Thursday.

&&

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

...UPDATED AVIATION DISCUSSION...

.SHORT TERM...Today Oct 18 through Tue Oct 20...Pretty big change
in temperatures between today and yesterday; 24 hours ago
temperatures were 5 to 12 degrees warmer in the coastal and
valley areas and 3 to 9 degrees cooler for the mountains and
deserts. The difference between this morning`s and yesterday`s low
temperatures is even more significant, with low temperatures
across the board 5 to up to 30 degrees cooler this morning
compared to yesterday. While offshore winds were present this
morning, they were light enough that they had little warming
effect, while keeping it dry and clear enough for efficient
radiational cooling.

Clear skies will continue today through most of tonight, though
there`s a chance for at least patchy dense fog to develop early
morning on Monday. The cooling trend present today in the coasts
and valleys will continue for Monday`s high temperatures with
another few degrees cooling, while the deserts and mountains warm
a couple additional degrees.

There is higher certainty in the return of the marine layer Monday
night into Tuesday morning, which will likely start out quite
initially low, if not leading to coastal dense fog, before likely
rising gradually through Tuesday morning. The cooling trend that
started in the coastal basin will continue for Tuesday, as well as
spread into the deserts as a low pressure system from the
northwest moves towards the area. A small handful of models are
indicating that light showers could start late Tuesday, generally
just for the inland mountains with increased onshore flow and
moisture perhaps leading to weak orographic lift, but the
majority keep Tuesday dry. Winds will be average for most areas
but start to pick up over the upper ridges into the High Desert
late in the afternoon Tuesday.

&&

.LONG TERM...Wed Oct 21 through Sunday Oct 25...A broad closed low
continues down the west coast Tuesday into Wednesday before
stalling just northwest of Pt Conception Wednesday afternoon, then
finally sweeping south towards the region late Wednesday. Onshore
winds will pick up Wednesday afternoon for the usual mountains,
desert slopes/deserts, and marine waters. These winds don`t look
to be significantly strong, with gusts likely in the 25 to 35 mph
range for the most part (to around 20 mph over the coastal
waters).

Rain chances increase through the day Wednesday; the current
forecast has widespread light to moderate rain moving through the
area late Wednesday through Thursday morning. South-southwest flow
as the rain band moves in will favor the San Bernardino
Mountains, where we`re expecting the most overall rainfall. The
front looks likely to weaken slightly as it passes through, with
lighter rain for south and east San Diego County compared to North
County, Orange County, and southwest San Bernardino County. Rain
rates will likely be steadily light to locally moderate through
this period.

Widespread rain gives way to scattered showers Thursday as the low
digs south, finally sweeping right over the area Thursday morning
into the afternoon along with the associated vort max. This will
bring 1000-700 MB instability of 350-500 J/kg to the area in turn
leading to widespread 15 to 25% chance for thunderstorms for the
mountains and areas westwards. Thunderstorms will bring the threat
for locally heavier rainfall as well as the usual dangerous
lighting, gusty winds, etc. so this may be the most potentially
impactful period during this event. Snow levels will drop
Thursday-Friday, but only to about 8000 feet, so it`s unlikely
that any area but the highest mountain peaks receive snow.

Showers gradually end sometime between late Thursday and Friday
morning. All in all, total rainfall for the region looks to be in
the range of 0.7" to about an inch for North County San Diego,
Orange County, and the northwest Inland Empire, with 1" to 1.3"
likely for the San Bernardino Mountains. South and east county San
Diego (including the mountains) as well as the southeast Inland
Empire and Riverside Mountains likely to get 0.4" to 0.7", with
0.2" to 0.5" in the High Desert and likely under 0.1" for the low
deserts. We`ve gotten an excellent head start on the Water Year
(which started Oct 1st), and this event will keep the trend going.

Models diverge on the location of the low going into next weekend,
with some showing the low stalling near AZ over the weekend and
others a smooth exit eastwards. In either case, temperatures will
start to rebound Friday through Sunday, and winds will likely turn
offshore for Saturday-Sunday. The strength of these winds varies
quite a bit between ensemble model members, with most of them at
this point looking pretty weak, but confidence will increase as
the week progresses. Looking out towards the end of the month,
some form of troughing is likely on the far horizon. The current
Climate Predication Center`s outlook for October 26 through
November 1 in southern California is for near normal temperatures
and leaning above average precipitation (50-60% chance).

&&

.AVIATION...190000Z...Coast...There is a 20-30 percent chance of low
clouds and patchy fog developing along the coastline, incl vicinity
of KSAN and KCRQ, 11-16Z. If clouds do manage to form on land, cigs
and vis will be very low, 200-500ft MSL and 0-3 SM respectively. Any
cloud coverage clears 16-18Z Mon.

Otherwise...VFR conditions expected with mostly SKC.

&&

.MARINE...
No hazardous marine conditions are expected through Tuesday. A storm
system moves into the region Wednesday through Thursday, bringing
possible local gusts around 20 knots and a chance (10-15%) for
thunderstorms Thursday.

&&

.BEACHES...
Elevated surf will continue through mid-week with multiple south
swells moving in. Expect surf of 3 to 6 feet and local sets to 7
feet along south and southwest-facing beaches through at least
Tuesday.

While surf and rip currents will be elevated, daily high tides will
not be particularly high, and the threat of coastal flooding is
minimal. Further details can be found in the Beach Hazard Statement.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through Tuesday morning for Orange
     County Coastal Areas-San Diego County Coastal Areas.

PZ...None.

&&

$$

PUBLIC...CSP
AVIATION/MARINE/BEACHES...Zuber

NWS San Diego (SGX) Office