115
FXUS66 KSGX 251956
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
1256 PM PDT MON AUG 25 2025
SYNOPSIS
THUNDERSTORMS DEVELOP TODAY OVER THE MOUNTAINS AND DESERTS WITH
HEAVY RAINFALL RATES AT TIMES POTENTIALLY EXCEEDING 1"/HR.
AFTERNOON MONSOON THUNDERSTORMS WILL BE POSSIBLE BOTH TUESDAY AND
WEDNESDAY AS WELL, WITH MORE CONSTRICTED COVERAGE IN THE
MOUNTAINS. A PATTERN CHANGE FOR THE LATTER HALF OF THE WEEK WILL
LIMIT THUNDERSTORMS AFTER WEDNESDAY, WITH MORE SEASONABLE
TEMPERATURES AND A DEEPENING MARINE LAYER. BY THE WEEKEND AND INTO
EARLY NEXT WEEK, A WARMING TREND SETS IN AND TEMPERATURES RETURN
ABOVE NORMAL.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
WATER VAPOR IMAGERY SHOWS HIGH PRESSURE OVER THE FOUR CORNERS REGION
TODAY, WHILE A DEEPENING LOW SPINS OFF THE COAST OF CALIFORNIA.
AMPLE MOISTURE PUSHES UP INTO THE DESERT SOUTHWEST TODAY, WITH PWS
EXCEEDING 1.5" ACROSS MUCH OF IMPERIAL COUNTY AND FAR EASTERN SAN
DIEGO AND RIVERSIDE COUNTIES. WIDESPREAD STORMS ARE EXPECTED TO
DEVELOP BEGINNING AROUND NOON, WITH FLASH FLOODING AS THE MAIN
THREAT. RAIN RATES COULD EXCEED 1"/HR AND SOME HI-RES GUIDANCE SHOWS
THE POSSIBILITY OF 2"+/HR, ESPECIALLY IN THE RIVERSIDE AND SAN DIEGO
MOUNTAINS. OUTSIDE OF THE FLOODING THREAT, THESE STORMS WILL ALSO BE
CAPABLE OF VERY GUSTY WINDS EXCEEDING 60 MPH AND DOWNBURST WILL
NOT BE OUT OF THE QUESTION GIVEN HIGHER CBS, ESPECIALLY FOR AREAS
FURTHER NORTH. WHILE LESS OF A CONCERN, SMALL HAIL MAY ACCOMPANY
ANY THUNDERSTORM THAT DEVELOPS. THE BEST CHANCES FOR STORMS TODAY
WILL BE IN THE SAN DIEGO COUNTY MOUNTAINS AND DESERTS, RIVERSIDE
MOUNTAINS, AND COACHELLA VALLEY. WITH THE INFLUX OF MID-LEVEL
MOISTURE TODAY, CLOUD COVER ALREADY STRETCHES FROM MUCH OF SAN
DIEGO COUNTY THROUGH IMPERIAL COUNTY AND INTO ARIZONA. THIS CLOUD
LAYER MAY ACTUALLY LIMIT SOME OF THE CONVECTION TODAY, BUT ALSO
PLAYS INTO THE AVAILABLE MOISTURE THAT STORMS WILL HAVE FOR THE
AFTERNOON.
MOST OF THE CONVECTION SHOULD END BY 6PM LOCAL TIME, WITH ONLY A FEW
LINGERING SHOWERS AND THUNDERSTORMS ACROSS THE HIGHER TERRAIN AS THE
HIGH BEGINS TO BREAK DOWN AND ELONGATES, WITH A BIG FLUX OF
MOISTURE THIS EVENING. AS THE AFOREMENTIONED LOW MOVES CLOSER TO
THE COAST, THUNDERSTORM CHANCES WILL SHIFT NORTHWARD FOR TUESDAY,
WITH THE HIGHER RAIN RATES (>1"/HR) SHIFTED TOWARDS THE SAN
BERNARDINO MOUNTAINS AND HIGH DESERTS FOR TUESDAY AFTERNOON.
TOMORROW LOOKS LIKE A RINCE-AND-REPEAT OF TODAY, JUST WITH THE
MAIN CORRIDOR OF MOISTURE AND STORMS SHIFTED TOWARDS THOSE
NORTHERN REGIONS. BY WEDNESDAY, THE LOW TRANSITIONS TO AN OPEN
TROUGH AND MOVES INLAND AND MONSOONAL THUNDERSTORM CHANCES DROP
FOR WEDNESDAY AND BEYOND. TEMPERATURES THROUGH THE END OF THE WEEK
HOLD STABLE, JUST AT OR SLIGHTLY BELOW NORMAL FOR AFTERNOON
HIGHS. AMPLE LINGERING MOISTURE IN THE DESERTS AND DESERT
FOOTHILLS WILL LIMIT OVERNIGHT LOWS FROM COOLING MUCH THROUGH THE
THE END OF THE WEEK, KEEPING THINGS A BIT WARMER ON THE EASTERN
SIDES OF THE MOUNTAINS. WITH HEIGHTS FALLING A BIT, THE MARINE
LAYER WILL BEGIN TO DEEPEN, MAKING IT FURTHER INLAND EACH NIGHT
AFTER WEDNESDAY. WEAK RIDGING BUILDS BACK IN THIS WEEKEND, AND
TEMPERATURES LOOK TO BEGIN TO WARM BY SUNDAY.
AVIATION
252100Z...COAST/VALLEYS...MID AND HIGH LEVEL CLOUDS AOA 10,000 FT
THIS AFTERNOON. LOW CLOUDS REDEVELOP AFTER 04Z TUE WITH BASES AROUND
900-1200 FT MSL MAKING IT 15-20 MILES INLAND BY 12Z. SCATTER OUT 16-
17Z.
MOUNTAINS/DESERTS...+SHRA/TSRA OVER THE MOUNTAINS ARE OCCURRING OVER
THE MOUNTAINS. CB BASES NEAR 10 KFT AND TOPS TO 30 KFT. GUSTY
OUTFLOW WINDS HIGHER THAN 35 KTS, 1-3 SM VIS IN +RA, SMALL HAIL, AND
LIGHTNING ARE POSSIBLE. 40-50% CHANCE A TSRA COULD DRIFT WITHIN 10
MILES OF KPSP AND KTRM UNTIL 01Z. CB/SHRA DISSIPATING THIS EVENING.
MORE +SHRA/TSRA TUESDAY AFTERNOON, SIMILAR TO TODAY.
MARINE
NO HAZARDOUS MARINE CONDITIONS ARE EXPECTED THROUGH FRIDAY.
SGX WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...NONE.
PUBLIC...ZUBER
AVIATION/MARINE...WESTERINK
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