756
FXUS66 KSGX 151615
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
915 AM PDT MON SEP 15 2025
SYNOPSIS
GRADUAL WARMING THROUGH TUESDAY, WITH GRADUAL COOLING FOR THE SECOND
HALF OF THE 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...
THE MARINE LAYER IS A COUPLE HUNDRED FEET SHALLOWER THAN YESTERDAY
MORNING. LOW CLOUDS REACHED THE WESTERN VALLEYS OVERNIGHT AND WERE
STARTING TO CLEAR INLAND AREAS AT 8 AM. LOW CLOUDS SHOULD CLEAR TO
THE COAST, BUT AREAS OF LOW CLOUDS MAY LINGER ALONG THE IMMEDIATE
COAST THIS AFTERNOON. THE MARINE LAYER WILL BECOME SHALLOWER INTO
TUESDAY, WITH DECREASING CHANCES OF WIDESPREAD LOW CLOUD COVERAGE
FOR THE MIDDLE TO END OF THE WEEK.
HIGHS TODAY ARE EXPECTED TO BE 5 TO 10 DEGREES WARMER THAN YESTERDAY
FOR VALLEY LOCATIONS AND A FEW DEGREES WARMER THAN YESTERDAY
ELSEWHERE. ADDITIONAL WARMING IS EXPECTED TUESDAY. BY 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 WEEK IS EXPECTED TO SEE
A GRADUAL COOLING TREND. THE COOLING TREND WILL BRING HIGH
TEMPERATURES BACK TO BELOW AVERAGE FOR MOST LOCATIONS BY NEXT
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 AS EARLY AS TUESDAY. IT LOOKS LIKE
THERE WILL BE ENOUGH MOISTURE AND FORCING FROM DIURNAL HEATING OVER
THE MOUNTAINS TO GENERATE SOME THUNDERSTORMS TUESDAY AFTERNOON. HIGH
RESOLUTION GUIDANCE FROM THE HRRR HAS HOURLY RAINFALL RATES PEAKING
AROUND 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. THOSE MOIST AND UNSTABLE CONDITIONS ARE
EXPECTED TO CONTINUE INTO NEXT WEEKEND, CONTINUING CHANCES FOR
SHOWERS AND THUNDERSTORMS. THE HIGHEST CHANCES OF SHOWERS AND
THUNDERSTORMS EACH DAY ARE IN THE MOUNTAINS AND DESERTS (30-60%)
DURING THE AFTERNOONS BUT SHOWERS/THUNDERSTORMS CANNOT BE RULED OUT
WEST OF THE MOUNTAINS. FOR AREAS WEST OF THE MOUNTAINS GUIDANCE IS
CURRENTLY SHOWING WEDNESDAY NIGHT INTO THURSDAY AND FRIDAY MORNING
HAVING THE HIGHEST CHANCES (20-35%) OF SHOWERS AND THUNDERSTORMS
DEVELOPING. FRIDAY THROUGH SUNDAY, MOISTURE WILL BEGIN TO DECREASE
BUT IT LOOKS LIKE THERE WILL BE ENOUGH TO BRING AFTERNOON SHOWERS
AND THUNDERSTORMS TO THE MOUNTAINS, POTENTIALLY INTO THE DESERTS.
AVIATION
151500Z...COAST/WESTERN VALLEYS...LOW CLOUDS BASED 1000-1500 FEET
MSL, TOPS TO 1900 FEET AND VIS 2-5SM OVER HIGHER COASTAL TERRAIN
WILL START CLEARING, 16-18Z, BUT WITH PATCHY LOW CLOUDS LINGERING
ALONG THE IMMEDIATE COAST THEREAFTER. LOW CLOUDS TO BECOME LOWER,
PATCHIER AND LESS UNIFORM IN COVERAGE TONIGHT AFTER 03Z. CIGS SHOULD
BE 700-1000 FEET, VIS 3-5SM CONFINED TO COASTAL AREAS.
INLAND VALLEYS/MOUNTAINS/DESERTS...MOSTLY CLEAR AND VFR CONDITIONS
THROUGH EARLY TUESDAY. SOME INCREASE IN CLOUDS AOA 10000 FEET
TONIGHT.
MARINE
THERE IS A SLIGHT CHANCE OF THUNDERSTORMS WEDNESDAY THROUGH FRIDAY.
ANY STORMS THAT DEVELOP COULD BRIEFLY PRODUCE GUSTY WINDS, CHOPPY
SEAS, AND LIGHTNING. OTHERWISE, NO HAZARDOUS MARINE CONDITIONS ARE
EXPECTED.
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...WESTERINK
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