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463
FXUS66 KSGX 222050
AFDSGX

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

.SYNOPSIS...
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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.
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&&

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

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 late tonight 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.
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&&

.AVIATION...
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221950Z...Coast/Valleys...Low clouds with bases near 1000 feet MSL
and tops near 1400 feet over the coastal waters today. After
23/0200Z this evening low clouds increasing in coverage with
bases around 1000 ft MSL and tops to 1400 ft MSL. Inland spread will
be restricted to the coastal areas and the western portions of the
San Diego County valleys. Bases could briefly drop below 1000 ft
MSL 12Z-15Z. Local VIS 1-3SM on elevated coastal terrain.

Low clouds could be erratic as monsoon moisture spreads over the
area overnight and even into Monday, so confidence in the timing and low
cloud amounts in the TAFs late tonight is low-moderate and likely
an even trickier CIG forecast Sunday night into Monday.

Tropical moisture is expected to arrive tonight through
Sunday morning. The moisture is enough with a weak disturbance to
bring a threat for widely scattered lightning and brief showers
Saturday night through Sunday.

Mountains/Deserts...Clear with unrestricted VIS then Tropical
moisture is expected to arrive Saturday night through
Sunday morning. Moisture is enough with a weak disturbance to
bring a threat for widely scattered lightning and brief showers
Saturday night through Sunday.
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&&

.MARINE...Tropical moisture is expected to arrive Saturday night
through Sunday morning. The moisture is enough with a weak
disturbance to bring a threat for widely scattered lightning and
brief showers Saturday night through Sunday. See the Marine weather
statement for more information.

&&

.BEACHES...
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There is a slight chance of thunderstorms Saturday night through
Sunday which could produce cloud-to-ground/cloud-to-water lightning
strikes. Chances of a lightning strike near any particular beach are
currently 5 percent or less Saturday night and Sunday. Rain
showers will generally be brief and light.
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&&

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

.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.

     Heat Advisory until 8 PM PDT this evening for Riverside County
     Mountains-San Bernardino County Mountains-San Diego County
     Mountains.

     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...CO
AVIATION/MARINE/BEACHES...Small