Area Forecast Discussion
Issued by NWS San Diego, CA

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205
FXUS66 KSGX 230415
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
915 PM PDT Sat Jun 22 2024

.SYNOPSIS...
Hot conditions expected for inland areas this weekend, with heat
continuing into next week for the deserts. A moisture surge tonight
and Sunday will increase the humidity and bring a slight chance of
showers and isolated thunderstorms to most areas. The best chances
of measurable rainfall and thunderstorm development is in the
mountains Sunday afternoon.

&&

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

.Evening Update...
Our sounding this evening shows more moisture present around 600mb
and PWAT values near 1.40", about double from this morning`s
launch. Mid-level clouds are seen moving up from the south this
evening over northern Baja into Arizona, while marine layer clouds
push slightly east near San Clemente Island. Most clouds should
stay out of the region tonight, with increasing clouds by the
morning hours.

Forecast changes this evening include lowering chances for
thunderstorms for areas west of the mountains tonight as the
environment is still a bit too dry to support any measurable
precipitation. Sunday still looks like the most active day with
moisture and instability in place. Best chances will be across
higher terrain into adjacent deserts, though latest hi-res models
have backed off on precip, indicating isolated activity mostly
over higher terrain. Chances on Monday continue to remain minimal,
mainly across the San Bernardino Mountains.

As stated below, it will be a hot and humid day tomorrow for much
of Southern California. Stay safe in the heat by wearing
sunscreen, drinking plenty of water, and taking breaks if
outdoors!

.Previous Discussion (150 PM Saturday)...
Widespread moderate to major heat risk continues away from the
the coast this weekend. Please be mindful if venturing outdoors
for recreation this weekend. Drink plenty of fluids and if
possible avoid strenuous outdoor activity between 10 am and 5 pm,
or take frequent breaks. A surge of moisture Sunday will knock
temperatures down a few degrees for inland areas and disrupt the
marine layer resulting in a couple degrees of warming along the
coast. The increase in humidity will make it harder to keep cool,
even if the official readings are a few degrees below today.

The moisture increase will also bring chances of showers and
isolated thunderstorms into Sunday. Models are showing our
forecast area being on the western edge of the action. As a result
shower and thunderstorm chances have trended down for overnight
tonight into early Sunday morning hours, with thunderstorm chances
around 5 percent. That being said, the influx of moisture is
still expected to increase precipitable water values to around
1.50" in the lower deserts, 1.25" west of the mountains and 1" in
the mountains Sunday. A weak shortwave coupled with the heat of
the day will generate mid-level lapse rates of 7.7C/km Sunday
afternoon and raise CAPE values to 500-600 J/kg. Chances for
showers and isolated thunderstorms are highest in the mountains
Sunday afternoon with a 30-35 percent chance of showers and a
10-15 percent chance of thunderstorms. West of the mountains,
chances of showers will be 15-20 percent with isolated
thunderstorm chances 5 percent or less. In the deserts shower
chances are closer to 20-25 percent with a 5-10 percent chance of
isolated thunderstorms. Best chances of accumulating precipitation
will be in the mountains, with little to no precipitation
expected to accumulate elsewhere. Enough moisture is expected to
remain in the atmosphere for isolated convection to again be
possible Monday afternoon, mainly over the San Bernardino
Mountains and High Deserts.

As the ridge remains over the Four Corners region, hot conditions
will continue through mid-week, especially in the deserts.
Temperatures in and west of the mountains will cool a few degrees
each day through mid-week, brining highs near to just below the
seasonal average. Coastal areas will keep a shallow marine layer,
which will moderate temperatures there. On Thursday, a trough of low
pressure moving into the Pacific Northwest will weaken the ridge
bringing a few additional degrees of cooling from the coast to the
deserts.

&&

.AVIATION...
230400Z...Coast/Valleys...Patchy BKN low clouds with bases 700-1000
ft MSL will occur near the immediate coast 07Z-17Z Sun. Chance of
a CIG at KSAN is 40-50 percent. Tops will be 1200 ft MSL, with local
VIS 3-5 miles over higher coastal terrain. There is around a 10
percent chance of TS 18Z Sun-02Z Mon, with highest chances in the
valleys. Otherwise, SCT-BKN clouds mostly at/above 9000 ft MSL will
prevail through Sun evening.

Mountains/Deserts...There is a 20-30 percent chance of TSRA 17Z Sun-
04Z Mon, with CB tops to 35000 ft MSL and possible strong
up/downdrafts and local surface wind gusts over 30 kt. Otherwise,
SCT-BKN clouds mostly at/above 9000 ft MSL will prevail through Sun
evening. Local west winds with gusts 25-35 kt will develop after 22Z
Sun, continuing Sun evening on the desert mountain slopes and into
the deserts and through San Gorgonio Pass.

&&

.MARINE...
Tropical moisture aloft will bring a very small chance of
thunderstorms (less than 10 percent at any one location)
mainly Sunday afternoon. Isolated cloud-to-water lightning strikes
will be possible, along with locally gusty winds. Wind gusts could
exceed 20 knots in the outer coastal waters Thursday.
Otherwise, no hazardous marine conditions will occur through
Thursday.

&&

.BEACHES...
There is a slight chance of thunderstorms mainly Sunday
afternoon which could produce cloud-to-ground/cloud-to-water
lightning strikes. Chance of a lightning strike near any particular
beach is around or less than 10 percent Sunday afternoon.
Rain showers will generally be brief.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 8 PM PDT Sunday for Orange County Inland
     Areas-San Bernardino and Riverside County Valleys-The
     Inland Empire-San Diego County Valleys.

     Excessive Heat Warning until 8 PM PDT Thursday for Apple and
     Lucerne Valleys-Coachella Valley-San Diego County Deserts-
     San Gorgonio Pass Near Banning.

PZ...None.

&&

$$

PUBLIC...APR/CO
AVIATION/MARINE...Maxwell/Zuber