648
FXUS66 KSGX 160333
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
833 PM PDT MON SEP 15 2025
SYNOPSIS
GRADUAL WARMING THROUGH TUESDAY, WITH GRADUAL COOLING FOR THE SECOND
HALF OF THE WORK WEEK. AN INFLUX OF TROPICAL MOISTURE WILL BRING
CHANCES OF SHOWERS AND THUNDERSTORMS FOR THE MIDDLE TO END OF THE
WEEK. HIGHEST CHANCES OF SHOWERS AND THUNDERSTORMS WILL BE IN THE
MOUNTAINS AND DESERTS, WITH LESSER CHANCES WEST OF THE MOUNTAINS.
THE MARINE LAYER WILL BECOME SHALLOWER EARLY IN THE WEEK, 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...
UPDATE: THE TROPICAL SYSTEM (MARIO), IS GOING TO PROVIDE A CHANCE OF
SHOWERS AND THUNDERSTORMS BY LATER IN THE WEEK, ALTHOUGH THERE IS
STILL SOME UNCERTAINTY WHERE EXACTLY THIS SYSTEM WILL TRACK. THE
LATEST UPDATE PROVIDED BY THE JOINT TYPHOON WARNING CENTER (JTWC)
ON MARIO SHOWS THE TRACK POSSIBLY TURNING IN A LITTLE MORE IN
TOWARDS LAND AS IT CONTINUES TO MOVE NORTHWESTWARD. THE MAY ALLOW
FOR THE REMNANTS OF THIS SYSTEM TO IMPACT THE REGION SLIGHTLY MORE
IF THE LOW PRESSURE CENTER OF THIS SYSTEM ENDS UP TRACKING A
LITTLE CLOSER TO SOCAL AS IT MAKES ITS WAY UP TOWARDS THE NORTH.
THE TIMING IS STILL SIMILAR, AND IT STILL LOOKS LIKE THE BEST
CHANCE OF SEEING SHOWERS/THUNDERSTORMS LOOKS TO BE EARLY THURSDAY
MORNING AS THE CONVERGENT SIDE OF THE SYSTEM MOVES OVER THE SAN
DIEGO AREA. THERE COULD ALSO BE A FEW THUNDERSTORMS DEVELOPING
OVER THE MOUNTAINS THROUGH THE UPCOMING WITH THE REINFORCEMENT OF
SOME MORE SUBTROPICAL MOISTURE FROM THE SOUTH IN THE MID-LEVELS.
OTHERWISE, THERE IS NOT MUCH CHANGE IN THE OVERALL PATTERN,
SHOWING MORE RIDGING BY EARLY NEXT WEEK, ALONG WITH A GRADUAL
WARMING TREND.
(PREVIOUS DISCUSSION SUBMITTED AT 137 PM):
AT 1 PM LOW CLOUDS HAD MOSTLY CLEARED FROM THE COAST AND WERE
LINGERING OFFSHORE. THE MARINE LAYER WILL BECOME SHALLOWER INTO
TUESDAY, WITH LOW CLOUD COVERAGE BECOMING MORE CONFINED TO THE COAST
AND WESTERN VALLEYS. FOR WEDNESDAY ONWARD, THERE ARE DECREASING
CHANCES OF WIDESPREAD LOW CLOUD COVERAGE WITH PATCHY TO NO LOW
CLOUDS EXPECTED.
HIGH TEMPERATURES WILL WARM 2 TO 5 DEGREES INTO TUESDAY. FOR TUESDAY
THE COAST AND VALLEYS WILL BE RUNNING 5 TO 10 DEGREES ABOVE AVERAGE
FOR THIS TIME OF YEAR WITH THE MOUNTAINS AND DESERTS ONLY 3 TO 5
DEGREES WARMER THAN AVERAGE. THE SECOND HALF OF THE WORK WEEK IS
EXPECTED TO SEE A GRADUAL COOLING TREND. THE COOLING TREND WILL
BRING HIGH TEMPERATURES BACK TO BELOW AVERAGE FOR MOST LOCATIONS BY
FRIDAY. LATEST NBM GUIDANCE IS SHOWING THE POTENTIAL FOR WARMER
CONDITIONS OVER THE WEEKEND.
MID TO UPPER LEVEL MOISTURE FROM TROPICAL STORM MARIO IS EXPECTED TO
BECOME ENTRAINED IN AN UPPER LEVEL AREA OF LOW PRESSURE OFF THE
COAST OF SOUTHERN CALIFORNIA TUESDAY. IT LOOKS LIKE THERE WILL BE
ENOUGH MOISTURE AND FORCING FROM DIURNAL HEATING OVER THE MOUNTAINS
TO GENERATE A FEW ISOLATED SHOWERS AND THUNDERSTORMS TUESDAY
AFTERNOON. HIGH RESOLUTION GUIDANCE FROM THE HRRR HAS HOURLY
RAINFALL RATES 0.50-0.75 INCHES PER HOUR, WITH MOST OF THE COVERAGE
ON THE MOUNTAIN RIDGES AND DESERT SLOPES. BY WEDNESDAY, THERE IS
EXPECTED TO BE A FURTHER INCREASE IN MOISTURE AND THE ENVIRONMENT IS
EXPECTED TO BECOME MORE UNSTABLE. LATEST GUIDANCE HAS THE BULK OF
THE WIDESPREAD RAINFALL OCCURRING WEDNESDAY EVENING INTO THURSDAY
AFTERNOON, WITH THE POTENTIAL FOR SHOWERS AND THUNDERSTORMS FROM THE
COASTAL WATERS TO THE DESERTS. BY THURSDAY AFTERNOON, CHANCES FOR
SHOWERS AND THUNDERSTORMS DECREASE FOR PLACES WEST OF THE MOUNTAINS
BUT REMAIN 60-70% FOR THE MOUNTAINS AND DESERTS. SHOWER AND
THUNDERSTORM CHANCES LESSEN THURSDAY NIGHT INTO FRIDAY, WITH THE
BEST CHANCES OF SHOWERS AND THUNDERSTORMS ON FRIDAY AFTERNOON IN THE
MOUNTAINS AND DESERTS. THE TROPICAL MOISTURE WILL SLOWLY DECREASE
THROUGH SUNDAY, BUT IT LOOKS LIKE THERE WILL BE ENOUGH REMAINING IN
THE ATMOSPHERE TO BRING AFTERNOON SHOWERS AND THUNDERSTORMS TO THE
MOUNTAINS, POTENTIALLY INTO THE DESERTS BOTH SATURDAY AND SUNDAY.
AVIATION
160300Z...COAST/WESTERN VALLEYS...LOW CLOUDS BASED 700-1000 FEET ARE
DEVELOPING OVER COASTAL WATERS. PATCHY COVERAGE OVER COASTAL LAND
AREAS AFTER 06Z, BUT LOW CONFIDENCE IN WIDESPREAD CIGS AND ONLY 5-10
MILES INLAND EXTENT AT MOST. PATCHY VIS REDUCTIONS 3-5 SM WITH LOWER
VIS POSSIBLE ALONG HIGHER COASTAL TERRAIN. ANY LINGERING LOW
CLOUDS ARE EXPECTED TO CLEAR 15-17Z TUE. HIGH CLOUDS AND INCOMING
TROPICAL MOISTURE SHOULD PREVENT ANY LOW CLOUD DEVELOPMENT TUESDAY
NIGHT.
INLAND VALLEYS/MOUNTAINS/DESERTS...VFR CONDITIONS THROUGH EARLY
TUESDAY. SLIGHT CHANCE TSRA OVER THE MTNS 21Z TUE TO 02Z WED. CB
BASES AOA 10000 FT MSL. LIGHTNING, GUSTY WINDS, AND REDUCED
VIS EXPECTED WHERE THUNDERSTORMS DEVELOP.
MARINE
SHOWERS LIKELY WITH A CHANCE OF THUNDERSTORMS
WEDNESDAY EVENING THROUGH THURSDAY MORNING ACROSS THE COASTAL
WATERS. SLIGHT CHANCE OF A LINGERING STORM OR TWO THURSDAY INTO
FRIDAY MORNING. ANY STORMS THAT DEVELOP COULD BRIEFLY PRODUCE GUSTY
WINDS, CHOPPY SEAS, AND LIGHTNING.
SKYWARN
SKYWARN ACTIVATION IS NOT REQUESTED. HOWEVER WEATHER SPOTTERS ARE
ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS.
SGX WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...NONE.
UPDATE...STEWEY
PUBLIC...CO
AVIATION/MARINE...KW
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