456
FXUS66 KSGX 040423
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
923 PM PDT Wed Jul 3 2024

.SYNOPSIS...
A long-duration heat wave will continue for the deserts through at
least the end of next week. Friday and Saturday are expected to
bet the hottest days for most areas. The marine layer will slow
the warming near the coast with night and morning coastal low
clouds spreading into the far western valleys late each night.
The extended period of hot and dry weather will lead to elevated
fire weather conditions each day.

&&

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

Evening update...
Marine layer low clouds are beginning to move back into the
coastal areas this evening with clear skies elsewhere. The 00Z
KNKX sounding shows the marine inversion based near 1500 ft MSL,
which is about 500 ft higher than this morning. Expect low clouds
to move into the far western valleys overnight with patchy fog
along the inland extent of the marine layer by tomorrow morning.
Clouds will clear at the beaches by the late morning or early
afternoon. They could redevelop along portions of the coast in
time for the evening fireworks displays, but will be high enough
to not interfere with viewing. Heat remains the main concern for
the Fourth of July, especially for inland areas, along with
elevated fire weather conditions due to hot and dry weather. While
high temperatures today were "only" around 5 to 8 degrees above
normal inland and no records were broken, tomorrow will be a few
degrees warmer. With it being a holiday filled with many outdoor
plans, make sure to stay hydrated, avoid strenuous activities like
hiking, wear light colored and lightweight clothing, and try to
stay in the shade - or better yet, indoors.

Previous discussion...
Friday and Saturday look to be the overall peak of this heat
event, when highs along and near the coast top out 5-10 degrees
above normal, while highs across all other inland areas range from
10-17 degrees warmer than seasonal average! Some areas in the
Coachella Valley and San Diego County Deserts, as well as
localized areas in the mountains and coastal valleys, look to set
multiple daily high temperature records. Friday in Palm Springs
will be an exceptional case, when the all-time daily high
temperature record of 123 degrees will be challenged.

Excessive Heat Warnings remain in effect for all desert zones
through next Wednesday, July 10, and are likely to remain in
place through at least the end of next week. Excessive Heat
Warnings also go into effect for the mountains of San
Bernardino/Riverside/San Diego Counties, the Inland Empire, and
the San Diego County Inland Valleys on Friday and Saturday, while
Heat Advisories will be in place for Inland Orange County and the
Santa Ana Mountains on Friday and Saturday as well. There will be
a slight drop in high temperatures on Sunday, followed by a
relatively steady high temperature forecast for early next week.
Keep in mind, its still going to be rather hot, with highs each
day topping out 5-10 degrees warmer than seasonal averages per
latest NBM guidance with anywhere from moderate to extreme
HeatRisk. The aforementioned tools suggest that an extension of
all heat warning/advisory products through more of next week very
well may be warranted.

What must absolutely not be lost in this story are the overnight
low temperatures in the deserts. Lows in the Coachella Valley and
San Diego County Deserts look to routinely only fall into the
middle 80s to low 90s overnight while the High Deserts see lows
in the middle to upper 70s, providing little to no overnight
relief.


&&

.AVIATION...
040400Z...Coast/Valleys...Areas of low clouds will spread up to 25
miles inland by 10Z Thu with bases 700-1200 ft MSL and tops to 1500
ft MSL. Local VIS will be 1-3 miles in BR in the coastal valleys and
higher coastal terrain 07Z-16Z Thu. Higher terrain will be locally
obscured. Most areas will clear 15Z-18Z Thu except for the immediate
coast which will have local BKN CIGs around 1000 ft MSL through Thu
afternoon. Low clouds will develop slightly later Thu evening with
similar heights.

Mountains/Deserts...Mostly clear skies with unrestricted VIS will
continue through Thu evening. Local west sfc winds 20-30 kt will
occur through San Gorgonio Pass 00Z-06Z Fri.

&&

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

&&

.BEACHES...
Long-period south swell (2-3 feet/16-18 seconds/190 degrees) will
build Thursday, peak Friday and Saturday, then gradually subside
Sunday and Monday. This will lead to elevated surf with breaking
wave heights up to 7 feet, mainly on exposed south and southwest-
facing beaches in Orange County. Rip and longshore current risks
will be high as well through Monday..

&&

.FIRE WEATHER...
A long duration heatwave combined with low daytime humidity and
sea breeze winds will bring elevated to near critical fire weather
conditions each day mainly during the afternoons and evenings. The
greatest risk will be in the lower elevations where there is
plenty of cured grasses. A persistent marine layer about
1000-1500 ft deep will keep areas near the coast cooler with
higher humidity. Energy Release Components are forecast to
steadily trend upward toward the 40th percentile and expected to
approach the 45th-50th percentile next week.

Extreme caution should be exercised with any activities that
produce a spark or flame, especially with the Fourth of July
holiday. Residents should heed any fire restrictions and bans.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement from Thursday morning through Sunday
     afternoon for Orange County Coastal Areas-San Diego County
     Coastal Areas.

     Excessive Heat Warning from 11 AM Friday to 9 PM PDT Saturday
     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.

     Heat Advisory from 11 AM Friday to 9 PM PDT Saturday for Orange
     County Inland Areas-Santa Ana Mountains and Foothills.

 Excessive Heat Warning until 9 PM PDT Wednesday July 10 for
Apple and Lucerne Valleys-Coachella Valley-San Diego County
Deserts- San Gorgonio Pass Near Banning.

PZ...None.

&&

$$

PUBLIC/FIRE WEATHER...SS/BA
AVIATION/MARINE/BEACHES...Maxwell