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428
FXUS66 KSGX 142058
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
158 PM PDT Mon Jul 14 2025

.SYNOPSIS...
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High pressure will weaken for tomorrow into Wednesday with
high temperatures as much as 8 to 12 degrees below average for
the valleys. For Thursday and Friday, a weak upper level low
pressure from the south will bring an increase in monsoonal
moisture with a chance of afternoon showers and thunderstorms,
mainly for the mountains and high desert with the greater chances
on Friday. Chances will slowly decrease during next weekend as the
monsoonal moisture slowly decreases. Night and morning coastal
low clouds will spread into the western valleys late each night.
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&&

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

Tonight through Wednesday...

High pressure conditions continue to dominate the region with a
ridge in place, although there more influence now from the troughing
upstream which has allowed for a cooldown to begin today that will
continue into Wednesday, with temperatures gradually dropping off
and becoming 10 to 15 degrees cooler than the seasonal average for
this time of year within the inland valleys and the onshore flow
becomes more enhanced. For the high deserts and the lower deserts
which are prone to gap flow winds, during the afternoon winds will
begin to increase and become gusty during the afternoon hours,
although should remain below the threshold of wind advisory
criteria. By Wednesday, highs will only make it into the low to mid
80s for most locations within the Imperial Empire (IE). The marine
layer will also continue to slightly lift and thicken up for the
overnight hours during this period in the forecast, with a very
slight chance of there being some very light drizzle, especially for
the inland areas during the early morning hours. There could also be
some patchy fog as well within some of the wind-sheltered inland
areas.

Thursday through early next week...

A weak upper level low south of the region will begin to slide more
to the north on Thursday. In the meantime, there will be an area of
high pressure centered over Arizona. This will allow for mid to
upper level winds to turn more southeasterly and result in come of
the subtropical monsoonal moisture from Mexico to be advected up
over SOCAL along with some weak upper level disturbances will allow
for a chance of thunderstorms over the mountains and deserts
beginning on Thursday. There could be a hindrance to thunderstorm
development on Thursday though, depending on how much mid-level
cloud coverage moves over during the morning hours, which might
help to keep things a slight bit more stable. By Friday, there
will be more moisture advected up over the area and further north,
although the mid-level flow will still be very weak out of the
southeast at the 700 mb level. This is alluding to there being the
best chance of thunderstorms on this day during the afternoon
hours. In addition, given the weak mid-level flow, some of these
storms may become stationary (or nearly stationary), which may
lead to potential flash flooding issues, especially if one of
these storms becomes situated right over a burn scar area.

By Saturday, the U/L low is going to begin to propagate further
towards the northeast and draw some of the moisture further towards
the east in the process. The ridge is also going to slightly build
into the weekend. As the U/L continues to move out of the region and
the mid level flow turns back to being more out of the southwest,
that will help to suppress thunderstorm development as drier air
aloft replaces the more moist and unstable southeasterly flow,
allowing for a lessening of probability of storms over the mountains
and deserts for both days, especially Sunday. The drying and slight
warming trend will continue into early next week.
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&&

.AVIATION...
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142030Z....Coast/Valleys...This morning`s clouds scattered to the
coast by 17-18z, but they have been pretty stubborn to fully clear,
with cloud cover lingering along the coasts and only a couple of
miles inland. These clouds (based at around 1200-1500) look to hang
around through the afternoon, with SCT-BKN CIGs possible for KSAN,
KCRQ, and KSNA. By 00-03z, clouds will surge back inland, with about
20 miles of inland extent by 06-09z Tuesday. KONT has a 65-75%
chance of CIGs between 11-16z Tuesday morning with a 25-35% chance
for KSBD, though localized VIS reductions to 4-6 SM in BR/HZ
possible in the Inland Empire and other inland valleys. Clouds
scattering back to the coast 16-18z Tuesday morning, but as what has
occurred today, beaches and immediate coasts could see clouds linger
into the afternoon.

Mountains/Deserts...FEW-SCT shallow Cu possible at 10-12 kft AGL
over the mountain ridges this afternoon. Otherwise clear skies with
unrestricted VIS through Tuesday afternoon.
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&&

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

.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...Munyan