Monsoonal moisture from the southeast produced showers and thunderstorms during the afternoon, lasting through early evening. The storms created brief heavy rains over a few areas, mainly in the San Diego County mountains and deserts.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS SGX wrote it up.
Monsoonal moisture from the southeast produced showers and thunderstorms during the afternoon, lasting through early evening. The storms created brief heavy rains over a few areas, mainly in the San Diego County mountains and deserts. Highway S2 near highway 78 in Shelter Valley received minor road flooding from a slow moving thunderstorm. Elsewhere, strong thunderstorms rumbled over the Santa Rosa mountains for 2-3 hours in the afternoon before drifting east over southern Coachella Valley near Oasis before dissipating. Flooding was not observed with these northern storms.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS San Diego, CA wrote its last area forecast discussion before the first event at Sep 4, 12:30 PM PST, 1 hour 15 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN DIEGO CA 130 PM PDT TUE SEP 4 2012 .SYNOPSIS... MOISTURE FROM THE SOUTHEAST WILL BRING SOME THUNDERSTORMS TO THE MOUNTAINS AND DESERTS THROUGH THURSDAY...MAINLY IN THE AFTERNOONS AND EARLY EVENINGS. OTHERWISE...WEAKENING HIGH PRESSURE ALOFT FROM NORTHERN BAJA TO TEXAS WILL COMBINE WITH A WEAK TROUGH OF LOW PRESSURE OFF THE CALIFORNIA COAST TO BRING A SLIGHT COOLING TREND WEDNESDAY THROUGH FRIDAY. HIGH PRESSURE ALOFT WILL REBUILD OVER THE WEEKEND FOR MORE WARMING...THEN ANOTHER WEAK TROUGH OVER THE WEST COAST WILL BRING A LITTLE COOLING EARLY NEXT WEEK. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... A FEW SHOWERS AND THUNDERSTORMS FORMED OVER THE SAN BERNARDINO AND SANTA ROSA MOUNTAINS EARLY THIS AFTERNOON. OTHERWISE...PARTLY CLOUDY SKIES PREVAILED WITH MOSTLY MID-LEVEL CLOUDS DUE TO THE MOISTURE FROM THE SOUTH. HUMID CONDITIONS CONTINUED IN THE LOWER DESERTS WITH DEW POINTS IN THE 70S IN MANY AREAS...EVEN THE UPPER 70S AT TIMES AT THERMAL. THE DRY AIR PREVIOUSLY OVER THE MTNS...ESPECIALLY WEST SLOPES...WAS GRADUALLY ERODING AS MOST DEW POINTS IN THE MTNS NOW ARE IN THE 40S AND 50S. EXPECT MOSTLY ISOLATED TSTORMS THROUGH VERY EARLY EVENING...WITH ACTIVITY EXPECTED SOON IN SAN DIEGO COUNTY DUE TO TSTORMS OVER N BAJA ABOUT 20 MI S OF THE SE CORNER OF SAN DIEGO COUNTY EXPECTED TO BUILD NW. MID-LEVEL MOISTURE WILL CONTINUE TO BE ABUNDANT THROUGH THURSDAY UNDER SOUTHERLY FLOW ALOFT. THE ITEM THAT WILL DETERMINE HOW MANY TSTORMS WILL FORM WILL BE THE INSTABILITY. THE MODELS...INCLUDING NAM/NAM4KM...UNDERESTIMATED THE LOW LEVEL MOISTURE IN THE DESERTS TODAY...AND I EXPECT SURFACE/NEAR SURFACE DEW POINTS THERE TO BE HIGHER AGAIN WED THAN THE MODEL SOLUTIONS. HENCE...INSTABILITY SHOULD BE HIGHER THAN WHAT THE MODELS SHOW. DUE TO INCREASING ONSHORE FLOW...ACTIVITY SHOULD BE CONFINED TO AREAS ALONG AND EAST/NORTH OF THE MTN CRESTS...ESPECIALLY DUE TO THE RECENT DROP IN SEA SURFACE TEMPERATURE WHICH WILL BRING A MORE STABLE ENVIRONMENT W OF THE MTNS ONCE THE ONSHORE FLOW INCREASES. ANY SORT OF DYNAMIC TRIGGER FROM THE TROUGH OFF THE CALIFORNIA COAST SHOULD STAY TO OUR NORTHWEST...BUT THIS IS WORTH MONITORING GIVEN THIS IS THE SEASON WHERE UPPER LOWS TO OUR WEST CAN SPARK TSTORM ACTIVITY W OF THE MTNS. MID LEVEL MOISTURE SHOULD EXIT TO THE NORTH AROUND FRI AND BRING AN END TO THE TSTORM CHANCES. AFTER TEMPS NEAR NORMAL IN MOST AREAS WED-FRI...THE UPPER HIGH WILL REBUILD OVER THE WEEKEND AND BRING WARMER WEATHER. A WEAK TROUGH IS PREDICTED FOR THE WEST COAST EARLY NEXT WEEK TO BRING SOME COOLING. && .AVIATION... 042030Z...ISOLATED SHOWERS AND THUNDERSTORMS ARE EXPECTED IN THE MOUNTAINS AND ADJACENT DESERTS THIS AFTERNOON WITH THEIR ASSOCIATED STRONG UPDRAFTS/DOWNDRAFTS. BASES WILL BE AROUND 10000 FEET ASL WITH TOPS UP TO 40000 FEET. VERY LITTLE IF ANY COASTAL LOW CLOUDS ARE EXPECTED TONIGHT...A PATCH OR TWO OF 500-1000 FOOT CIGS AT KSAN AND/OR KCRQ AT MOST...ANYTIME BETWEEN 08-15Z WEDNESDAY MORNING. MORE THUNDERSTORMS ARE EXPECTED IN THE MOUNTAINS AND DESERTS WEDNESDAY AFTERNOON. && .SGX WATCHES/WARNINGS/ADVISORIES...NONE. && PUBLIC...MAXWELL AVIATION...MM
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE SAN DIEGO CA 700 AM PDT TUE SEP 4 2012 CAZ055-056-058-060>062-050030- SAN BERNARDINO COUNTY MOUNTAINS-RIVERSIDE COUNTY MOUNTAINS-SAN DIEGO COUNTY MOUNTAINS-APPLE AND LUCERNE VALLEYS-COACHELLA VALLEY-SAN DIEGO COUNTY DESERTS- 700 AM PDT TUE SEP 4 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE MOUNTAINS AND DESERTS OF EXTREME SOUTHWESTERN CALIFORNIA. .DAY ONE...TODAY AND TONIGHT SLIGHT CHANCE OF THUNDERSTORMS OVER THE MOUNTAINS AND DESERTS. THE FLASH FLOOD POTENTIAL IS LOW. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY WEDNESDAY THROUGH THURSDAY...CHANCE OF THUNDERSTORMS OVER THE MOUNTAINS AND DESERTS WEDNESDAY AND SLIGHT CHANCE OF THUNDERSTORMS THURSDAY. THE FLASH FLOOD POTENTIAL IS LOW TO MODERATE WEDNESDAY...THEN LOW THURSDAY. FRIDAY THROUGH MONDAY... .SPOTTER INFORMATION STATEMENT... SKYWARN WEATHER ACTIVATION IS NOT REQUESTED FOR THIS AREA. HOWEVER...WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS. MAXWELL
The national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
Four inches of water flowing over highway S2 near highway 78 in an area known as Scissors Crossing. Road remains passable.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2012Every state in 2012This day in weather historyWarnings in California, September 2012
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 411602.