217
FXUS66 KSGX 162044
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
144 PM PDT TUE SEP 16 2025
SYNOPSIS
REMNANTS OF TROPICAL STORM MARIO WILL BRING INCREASING MOISTURE AND
CLOUDS TO THE AREA FOR THE MIDDLE OF THE WEEK. THERE ARE CHANCES OF
SHOWERS AND THUNDERSTORMS FOR THE MOUNTAINS AND DESERTS FROM THIS
AFTERNOON THROUGH EARLY NEXT WEEK. FOR WEDNESDAY THROUGH FRIDAY
MORNING THERE ARE CHANCES FOR SHOWERS AND THUNDERSTORMS WEST OF THE
MOUNTAINS. THE MARINE LAYER WILL BECOME SHALLOWER WITH THE POTENTIAL
FOR MINIMAL OR NO LOW CLOUD COVERAGE FOR THE MIDDLE TO END OF THE
WEEK.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
SATELLITE AT 1 PM WAS SHOWING AREAS OF CUMULUS CLOUDS OVER THE
MOUNTAINS, LOCALLY INTO THE VALLEYS. NO PRECIPITATION HAS BEEN
DETECTED THUS FAR, ALTHOUGH CONVECTION HAS DEVELOPED IN THE
MOUNTAINS SOUTH OF THE BORDER. THE 12Z KNXK SOUNDING WAS SHOWING
1.25 INCHES OF PRECIPITABLE WATER WITH 700 J/KG OF MOST UNSTABLE
CAPE. ONE INHIBITING FACTOR IS A FAIRLY SUBSTANTIAL INVERSION NEAR
700 MB. THIS COULD LIMIT CONVECTIVE DEVELOPMENT, EVEN WITH THE
OTHERWISE FAVORABLE CONDITIONS. THE SLIGHT CHANCES OF SHOWERS AND
THUNDERSTORMS OVER THE MOUNTAINS HAS BEEN MAINTAINED IN THE
AFTERNOON FORECAST PACKAGE.
CHANCES FOR SHOWERS AND THUNDERSTORMS BECOME MORE WIDESPREAD FOR
WEDNESDAY AFTERNOON THROUGH EARLY FRIDAY MORNING. IT LOOKS LIKE
THERE WILL BE ENOUGH MOISTURE AND INSTABILITY TOMORROW AFTERNOON FOR
THUNDERSTORMS TO DEVELOP OVER THE MOUNTAINS, LOCALLY INTO THE
DESERTS AHEAD OF THE MAIN MOISTURE SURGE. AS WE MOVE INTO WEDNESDAY
EVENING AND THURSDAY MORNING, SHOWER CHANCES BECOME MORE WIDESPREAD
WEST OF THE MOUNTAINS, WITH THE POTENTIAL FOR ISOLATED THUNDERSTORMS
TO DEVELOP. SHOWER COVERAGE OVERNIGHT MAY BE FAIRLY SCATTERED. FOR
THURSDAY AFTERNOON, SHOWER AND THUNDERSTORM CHANCES CONTINUE FOR THE
INLAND VALLEYS, MOUNTAINS, AND DESERTS. DEPENDING ON HOW STRONG THE
EASTERLY FLOW IS, IT'S POSSIBLE THUNDERSTORMS COULD DRIFT CLOSER TO
THE COAST. FLASH FLOODING IS POSSIBLE WHERE THUNDERSTORMS DEVELOP,
ESPECIALLY IN THE MOUNTAINS AND DESERTS. OTHERWISE, MAIN IMPACTS
WILL BE FREQUENT LIGHTNING AND THE POTENTIAL FOR URBAN FLOODING
WHERE SHOWERS/THUNDERSTORMS DEVELOP WEST OF THE MOUNTAINS. BASED ON
THE LATEST HIGH RESOLUTION GUIDANCE RAINFALL RATES WEST OF THE
MOUNTAINS WILL GENERALLY BE 0.25"/HR OR LESS, BUT COULD BE LOCALLY
HIGHER WHERE THUNDERSTORMS DEVELOP; IN THE MOUNTAINS RAINFALL RATES
LOOK TO BE AROUND 1"/HR; AND 0.50"/HR IN THE DESERTS.
HIGH RESOLUTION GUIDANCE IS INDICATING SOME LINGERING ISOLATED
HEAVIER SHOWERS OR THUNDERSTORMS OVERNIGHT THURSDAY INTO FRIDAY
MORNING. FOR FRIDAY, IT LOOKS LIKE THE BEST CHANCES OF SHOWERS AND
THUNDERSTORMS WILL BE OVER THE MOUNTAINS POTENTIALLY INTO THE
DESERTS. CHANCES FOR AFTERNOON SHOWERS AND THUNDERSTORMS WILL
CONTINUE FOR THE MOUNTAINS, DESERTS, AND POTENTIALLY INLAND VALLEYS
INTO EARLY NEXT WEEK.
THE INCREASE IN MOISTURE AND CLOUDS, WEDNESDAY AND THURSDAY WILL
RESULT IN HIGH TEMPERATURES FOR INLAND AREAS TO COOL SEVERAL
DEGREES. HIGH TEMPERATURES ON THURSDAY WILL BE AS MUCH AS 8 TO 12
DEGREES BELOW AVERAGE FOR THE MOUNTAINS. HIGH TEMPERATURES FOR
INLAND AREAS WILL WARM AROUND 10 DEGREES FROM THURSDAY THROUGH
SUNDAY WITH SUNDAY HIGH TEMPERATURES MOSTLY A FEW TO AROUND 5
DEGREES BELOW AVERAGE. HIGH TEMPERATURES ON SUNDAY WILL RANGE FROM
THE MID 70S NEAR THE COAST TO THE UPPER 80S TO MID 90S FOR THE
INLAND EMPIRE WITH THE MID 90S TO AROUND 100 FOR THE LOWER DESERTS.
THERE COULD BE ANOTHER INFLUX OF TROPICAL MOISTURE EARLY NEXT WEEK
FROM A SECOND TROPICAL SYSTEM THAT IS YET TO FULLY DEVELOP. MORE
INFORMATION WILL BE AVAILABLE IN THE COMING DAYS.
AVIATION
162000Z...COAST...LOW CLOUDS GENERALLY NOT EXPECTED TONIGHT INTO
WEDNESDAY WITH LOW TO MODERATE CONFIDENCE. CLOUDS WILL BE VERY
PATCHY WITH BASES 300-700 FEET MSL. IF ANY CLOUDS FORM, THEY WILL
FORM BETWEEN 09-17Z WED.
VALLEYS/MOUNTAINS/DESERTS...VFR CONDITIONS THROUGH TONIGHT. CLOUDS
OVER MOUNTAINS WILL CONTINUE A SLIGHT CHANCE TSRA UNTIL 01Z. CB
BASES AOA 10000 FEET MSL, WITH TOPS REACHING 30000 FEET MSL.
LIGHTNING, GUSTY WINDS, AND REDUCED VIS EXPECTED WHERE ANY TSRA
DEVELOPS.
REGIONWIDE...SCT CLOUDS BECOMING BKN AROUND 10000 FEET MSL AFTER 00Z
THROUGH MUCH OF WEDNESDAY. ISO TSRA ACROSS ALL AREAS AFTER 18Z WED
WITH CLOUD BASES AOA 10K FT MSL; STORM CHANCES INCREASING ON
THURSDAY.
MARINE
THERE IS A SLIGHT CHANCE OF THUNDERSTORMS WEDNESDAY
THROUGH FRIDAY, WITH THE GREATEST CHANCE ON THURSDAY AFTERNOON AND
EVENING. ANY STORMS COULD BRIEFLY PRODUCE LIGHTNING, GUSTY WINDS AND
CHOPPY SEAS. QUIETER CONDITIONS EXPECTED OVER THE WEEKEND.
BEACHES
THERE IS A SLIGHT CHANCE OF THUNDERSTORMS WEDNESDAY
THROUGH FRIDAY, WITH THE GREATEST CHANCE ON THURSDAY AFTERNOON AND
EVENING. STORMS MAY BE ACCOMPANIED BY CLOUD TO GROUND LIGHTNING AND
GUSTY WINDS.
APR
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...CO
AVIATION/MARINE/BEACHES...APR
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