929
FXUS66 KSGX 140422
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
922 PM PDT SAT SEP 13 2025
SYNOPSIS
NEAR TO SLIGHTLY BELOW NORMAL TEMPERATURES THROUGH MONDAY. A SLOW
WARMING TREND WILL BRING A SHALLOWER MARINE LAYER AND NEAR NORMAL
TO ABOVE NORMAL TEMPERATURES BY WEDNESDAY. AN ISOLATED
THUNDERSTORM OR TWO WILL POSSIBLE FOR AREAS WEST OF THE MOUNTAINS
TUESDAY INTO WEDNESDAY MORNING. AMPLE MONSOONAL MOISTURE RETURNS
BY WEDNESDAY, WITH THUNDERSTORM CHANCES MAINLY IN THE MOUNTAINS
EACH AFTERNOON AND EVENING THROUGH THE WEEKEND.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
EVENING UPDATE...
LOW CLOUDS STRUGGLED TO CLEAR COMPLETELY OVER THE COASTAL AREAS
THIS AFTERNOON, RESULTING IN MORE WIDESPREAD CLOUD COVER THIS
EVENING. THE 00Z KNKX SOUNDING SHOWS THE MARINE INVERSION
REMAINING NEAR 2800 FT MSL. THIS MAY DROP SLIGHTLY OVERNIGHT AS A
WEAK TRANSITORY RIDGE BEGINS TO MOVE OVER THE REGION, BUT WILL
REMAIN DEEP ENOUGH TO ALLOW CLOUDS TO FILL IN MOST OF THE COASTAL
BASIN AGAIN TONIGHT.
NO CHANGES TO THE FORECAST THIS EVENING, THOUGH LATEST EC AND GFS
ENSEMBLES SHOW MAIN MOISTURE PLUME AND WEAK ELEVATED INSTABILITY
OVER THE COASTAL WATERS AND AREAS WEST BEGINNING LATE TUESDAY
MORNING WITH GENERALLY LOW (LESS THAN 10%) CHANCES OF THUNDER. THE
REST OF THE WEEK WILL LARGELY DEPEND ON WHERE THE UPPER LOW OFF
THE COAST SETS UP AND DRAWS IN MOISTURE, THOUGH MODELS ARE COMING
INTO BETTER CONSENSUS WITH THAT.
PREVIOUS DISCUSSION...
MID-LEVEL WATER VAPOR IMAGERY CURRENTLY SHOWS A WEAK SHORT WAVE
RIDGE MOVING INTO SOUTHERN CALIFORNIA. DESPITE THE INCREASING
HEIGHTS, A SECONDARY SHORTWAVE TROUGH OFF THE COAST IS HELPING TO
MODERATE OUR WARM UP TOMORROW, WITH TEMPERATURES REMAINING NEAR
OR BELOW NORMAL IN THE 60S AND 70S FOR INLAND/COAST/MOUNTAINS AND
80S TO 90S FOR THE DESERTS. SUNDAY INTO MONDAY, THIS SHORTWAVE
WILL BECOME A CLOSED LOW AND SLOWLY BEGIN TO TREK NORTHWARD ALONG
THE COAST OF CALIFORNIA AS A TROPICAL SYSTEM TO THE SOUTH PIVOTS
TO THE NORTHWEST. MODELS ARE BEGINNING TO HINT AT THE POSSIBILITY
OF SOME INFLUENCE FROM THIS SYSTEM AS IT MOVES WEST, WHICH MAY
HELP INITIATE SOME STORMS EARLIER IN THE WEEK THAN PREVIOUSLY
EXPECTED. IF THIS OCCURS, RAIN OR THUNDERSTORMS WILL NOT BE OUT OF
THE QUESTION, PRIMARILY SAN DIEGO COUNTY AND OFFSHORE, AS EARLY
AS TUESDAY/WEDNESDAY MORNING. FOR NOW, CHANCES ARE ONLY AROUND
10-15%.
A LESSER PRESSURE GRADIENT WILL SEE WEAKER ONSHORE FLOW INTO MID-
WEEK, ALONG WITH A MORE SHALLOW MARINE LAYER, AND TEMPERATURES
WILL WARM FOR MUCH OF THE INLAND AND COASTAL AREAS. HIGHS LOOK TO
PEAK WEDNESDAY FOR AREAS WEST OF THE MOUNTAINS, AROUND 4-7 DEGREES
ABOVE NORMAL, BEFORE A SLOW COOL DOWN SETS IN FOR THE REST OF THE
WEEK. AS MENTIONED THE PAST FEW DAYS, MONSOONAL MOISTURE IS
EXPECTED TO MAKE A RETURN FOR MUCH OF THE REGION BY WEDNESDAY,
WITH INCREASING THUNDERSTORM CHANCES FOR THURSDAY ONWARD.
CURRENTLY, THE BEST CHANCES FOR STORMS WILL EXIST IN THE MOUNTAINS
EACH AFTERNOON AND EVENING, BUT A FEW STORMS MAY MAKE IT INTO THE
DESERTS AND VALLEY AREAS. ANY STORMS THAT MANAGE TO DEVELOP WILL
BE ACCOMPANIED BY BRIEF, HEAVY RAIN, GUSTY AND ERRATIC WINDS, AND
FREQUENT LIGHTNING. RAIN RATES EXCEEDING 0.50"/HR WILL BE
POSSIBLE, WITH THE BEST CHANCES FOR THE SAN DIEGO AND RIVERSIDE
MOUNTAINS. ALONG WITH THE THUNDERSTORM THREAT, THE UPTICK IN
MOISTURE ACROSS THE DESERTS AND MOUNTAINS SHOULD LIMIT HEATING
EACH DAY, WITH MORE SEASONABLE TEMPERATURES EXPECTED NEXT WEEK.
HIGHS GENERALLY WILL RANGE FROM THE MID 90S TO LOW 100S FOR THE
DESERTS, AND 70S FOR THE MOUNTAINS.
MODELS CONTINUE TO STRUGGLE WITH THE UPPER LEVEL PATTERN LATE THIS
WEEK, ALTHOUGH THERE SEEMS TO BE GENERAL SUPPORT IN THE LONG-RANGE
OF PERSISTENT MONSOONAL MOISTURE AS MULTIPLE TROPICAL SYSTEMS MOVE
WESTWARD, AND A CUTOFF LOW SEPARATES FROM THE LARGER TROUGH OVER THE
PACNW, SETTING UP JUST OFFSHORE. WHILE CONFIDENCE IS LOW IN THE
MODEL GUIDANCE THIS FAR OUT, THERE SEEMS TO BE PRETTY GOOD ALIGNMENT
ON SUCH A PATTERN THAT WOULD SUPPORT AFTERNOON CONVECTION AND COOLER
TEMPERATURES INTO THE LATTER HALF OF SEPTEMBER. AFTER A ABNORMALLY
HOT SEPTEMBER LAST YEAR AND THE DRIEST START TO THE WATER YEAR, A
COOLER START TO FALL AND SOME MUCH NEEDED MOISTURE WOULD BE VERY
WELCOME.
AVIATION
140300Z...COAST/VALLEYS...PATCHY LOW CLOUDS BASED 1500-2000 FT MSL
OVER COASTAL AREAS HAVE BEGUN TO EXPAND IN COVERAGE. CLOUDS WILL
CONTINUE TO FILL INTO SAN DIEGO AND ORANGE COUNTIES UP TO 20 MILES
INLAND THROUGH 09Z. THEREAFTER, CLOUDS WILL PUSH INTO PORTIONS OF
THE INLAND EMPIRE. 60% CHANCE CIGS AT KONT AND 50% AT KSBD.
SCATTERING BACK TO THE COASTS 16-18Z, LIKELY WITH LESS CLOUDS
LINGERING ALONG THE COASTS COMPARED TO TODAY. LOW CLOUDS BEGIN TO
MOVE INLAND AGAIN 00-03Z MONDAY, BUT WITH SLIGHTLY LOWER BASES AND
LESS INLAND EXTENT.
MOUNTAINS/DESERTS...MOSTLY CLEAR AND VFR CONDITIONS THROUGH SUNDAY
EVENING.
MARINE
NO HAZARDOUS MARINE CONDITIONS ARE EXPECTED THROUGH THURSDAY.
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...SS/ZUBER
AVIATION/MARINE...KW
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