Area Forecast Discussion
Issued by NWS San Diego, CA

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516
FXUS66 KSGX 241603
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
903 AM PDT Wed Jul 24 2024

.SYNOPSIS...
Monsoonal moisture remains in place across southern California
today for additional thunderstorms over the mountains and deserts.
Strong upper ridge is situated over northern Arizona. There will
be drying and warming on Thursday. The air mass dries out further
into the weekend as an upper low pressure system moves across
northern California with onshore southwest flow. There will also
be a cooling trend for Friday through Sunday with weekend high
temperatures near averages and more marine cloud and air influence
for the coast and valleys producing slightly below average
temperature. A slow warming trend for next week.

&&

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

Thin patchy marine stratus on the San Diego coast this morning
otherwise monsoon moisture remains in place with 1.3 to 1.5 inch
precipitable water, highest in Imperial Valley, per the Storm
Prediction analysis. There is also a cluster of thunderstorms
being triggered by a mid level disturbance over the Imperial
Valley in 2000 joules of CAPE just above the surface. Otherwise
surface based convection will wait for heating and upslope flow
over the spine of the mountains and helped by the afternoon sea
breeze making it up to 3000-4000 feet for better convergence along
the crest opposing the easterly upslope flow from the hot desert.
The difference today is the steering flow has shifting to south
instead of easterly, so there will be less anchoring but cells
will drift northward along the spine natural convergence zone.
Upper high is forecast to settle over northern Arizona today and
reach 599-600 DM at 500 mb. Potential for a couple cells to have
heavy rain and strong gusty winds this afternoon though coverage
slightly less than yesterday.

Air mass of 28 to 31C is in place today and Thursday but we will
have warmer temperatures on Thursday as the air mass dries. Very
slight cooling on Friday expect the lower deserts nearly same and
up around 116F. Max potential is 118F if enough drying occurs in
the deserts.


You can find thunderstorm reports in the Local Storm Report
LSRSGX.

On Thursday 598 DM upper ridge shifts into central Arizona and on
the backside this allows a drier but light southwest flow to
nudge into Socal. Still an isolated thunderstorm on the mountain
crest on the desert slopes possible before much drier air arrives
by Friday. This drying and stronger southwest flow is associated
with a short wave trough that cuts across northern California
during Friday afternoon.

The weekend will be dry and notably cooler, especially inland,
with highs only near averages. Next week upper high sets
up over the Great Basin or Socal for a warming trend as it
rebuilds to 600 DM. Considerable differences in the location of
this upper ridge makes for uncertainty.

&&

.AVIATION...
241530...Coast...Patchy low clouds at 1000 feet MSL will stick to
parts of the immediate coast today with gradual clearing. Patchy low
clouds to gradually increase overnight into Thursday mainly in San
Diego County. Cigs around 1000 feet MSL most likely near KSAN and
KCRQ along with vis 3-5SM in BR on mesas from 10-15Z.

Mountains/Deserts...up to 30% chance of TSRA over the mountains and
high desert (most likely near KL35) between 19-01Z. SCT-BKN CB based
9000-12000 feet MSL with tops up to 35000 feet. Lightning and strong
erratic winds near any storms.

Otherwise, mostly clear through Thursday morning except for
scattered blow off clouds from TS above 12000 feet MSL this
afternoon.

&&

.MARINE...
No hazardous marine conditions are expected through Sunday.

&&

.FIRE WEATHER...
Monsoon moisture in place despite the heat which helps for fire
weather conditions. However, drying is significant by Friday and
slightly increase to onshore southwest flow will raise fire
weather to elevated.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 10 PM PDT Thursday for Riverside County
     Mountains-San Bernardino County Mountains-San Bernardino
     and Riverside County Valleys-The Inland Empire-San Diego
     County Mountains-San Diego County Valleys.

     Excessive Heat Warning until 10 PM PDT Thursday for Apple and
     Lucerne Valleys.

     Excessive Heat Warning until 8 PM PDT Friday for Coachella
     Valley-San Diego County Deserts-San Gorgonio Pass Near
     Banning.

PZ...None.

&&

$$

PUBLIC/FIRE WEATHER...Tardy
AVIATION/MARINE...MM