072
FXUS66 KSGX 291028
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
328 AM PDT Sun Jun 29 2025

.SYNOPSIS...
Another hot day is in store for us today, and continuing into
tomorrow for the deserts with a strong subtropical ridge in place
over the desert southwest. This is resulting in temperatures
across the inland valleys reaching the upper 80s to low 90s in the
San Diego county valleys and the mid to upper 90s for the Inland
Empire, while the deserts see highs 105-110. The marine layer
lowers some this weekend, but lifts again early next week, with
night and morning coastal low clouds spreading into the western
valleys, clearing by the mid-late mornings. Through this stagnant
pattern, the deserts stay hot Monday into Tuesday while the inland
valleys are a little cooler. This fairly stagnant upper level
pattern will persist through mid-week, then a trough with an
associated upper level low will slide eastward over California on
from Wednesday into Thursday. This could allow for a rogue shower
or storm over the mountains and deserts during the afternoon on
Tuesday ahead of the trough moving overhead. The pattern begins to
grow more uncertainty Thursday through the end of the week.
Within this uncertainty, what appears more certain is the increase
in monsoonal activity, although staying east of SoCal.

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

The subtropical ridge axis has begun to shift slightly towards the
east, with the center of the high located roughly over the AZ/NM
border. As a trough upstream over the Pacific slowly inches closer
to California, it will allow for the ridge to further weaken and
move east. Given how strong the ridge is, today will be very warm
and downright hot for the deserts as it was yesterday. By tomorrow,
the coastal and inland areas will begin to feel the influence of the
trough with temperatures beginning to cool slightly from where they
will be for highs today. Despite this, the deserts will still be
rather hot tomorrow and some increase of moisture from the south
(with dewpoints in the 40s and 50s) is going to increase the heat
index. Values are hovering right around the threshold for an
Excessive Heat Warning. However, there are not enough widespread
values exceeding the moderate category to warrant the issuance of an
EHW at this time, it is still advised to be cautious and stay well
hydrated if planning to go out to the deserts on Monday, as
temperatures are expected to climb above 110F within the Coachella
Valley and portions of the lower deserts in San Diego County.

Tuesday through next weekend...

The troughing over the eastern Pacific waters, with an upper level
low centered just west of Point Conception by the morning of
Tuesday, is going to continue to slowly propagate towards the
region. Although there are signs that the monsoonal pattern might be
setting up, with a substantial amount of subtropical moisture at the
700-500 mb level over central Mexico, the trough to the west is
going to help to suppress and hinder the moisture making it back
towards the west and over our CWA. That being said, there could
still be enough instability with the U/L low to help kick off an
isolated shower and possible thunderstorm over the higher terrain
and deserts (mainly over the deserts). Some of the deterministic
models, such as the Canadian, do show that there could be some
potential showers and thunderstorms developing over the mountains
and deserts on Tuesday afternoon. This feature will also begin a
cooldown, and the slow progression of this trough/low towards the
east will keep temperatures on the cooler side with a subtle
downward trend towards the end of the week. This could also help to
enhance the marine layer with some drizzle being possible for the
coastal and inland areas during the overnight hours Tuesday and
Wednesday night.

The low will eventually fill and become absorbed back into the
longwave trough as it begins to flatten with the longwave pattern
transitioning back to more zonal flow. This will help to keep
temperatures generally the same going into the following weekend,
with temperatures right around, or slightly below, the seasonal
average for this time of year.

&&

.AVIATION...
290930Z....Coast/Valleys...Low clouds based 600-1000 ft MSL continue
to slowly push into coastal SD/Orange Counties. BKN CIGs should
reach up to 15 miles inland by 12z. Vis of 1-4SM for western valleys
and higher coastal terrain, locally below 1SM 11-14z Sun. Clearing
to the coast 15-17Z. 30% chance CIGs remain BKN at SD County beaches
through the afternoon. Regardless, low clouds with similar bases
return to coastal land areas 03-06z Monday.

.Mountains/Deserts...SW/W wind gusts 25-35 kts across the deserts
and mountain passes Sunday afternoon 20Z-05Z Mon leading to MOD
UDDFS just east of the mountains. Winds weaken again by overnight
Sunday.

&&

.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...Stewey
AVIATION/MARINE...KW