Isolated monsoon activity occurred on the 21st and 22nd from continued moist, southeast flow into southern California. This activity was mainly concentrated 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.
Isolated monsoon activity occurred on the 21st and 22nd from continued moist, southeast flow into southern California. This activity was mainly concentrated in the San Diego County mountains and deserts. Several reports of roadway flooding and debris occurred with these thunderstorms.
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 Aug 21, 9:20 AM PST, 3 hours 40 minutes earlier.
AREA FORECAST DISCUSSION...CORRECTION
NATIONAL WEATHER SERVICE SAN DIEGO CA
1020 AM PDT TUE AUG 21 2012
CORRECTION TO REMOVE LONG TERM SECTION...NO OTHER CHANGES
.SYNOPSIS...
A SURGE OF MONSOON MOISTURE OCCURRED OVERNIGHT THAT HAS MADE THE AIR
MASS OVER SOUTHWEST CALIFORNIA MOIST AND UNSTABLE ENOUGH FOR
THUNDERSTORMS TODAY WITH HEAVY DOWNPOURS. SOME OF THESE COULD LEAD
TO FLASH FLOODING...MAINLY OVER THE MOUNTAINS AND DESERT AREAS.
THERE IS ALSO A SLIGHT CHANCE OF THUNDERSTORMS CONTINUING THROUGH
THE NIGHT...SOME OF THESE MAY AFFECT THE COAST AND INLAND VALLEY
AREAS. THUNDERSTORMS ARE AGAIN POSSIBLE ON WEDNESDAY. A TROUGH
MOVING INLAND WILL BRING DRIER SOUTHWEST FLOW ALOFT WEDNESDAY NIGHT
THROUGH THURSDAY. THIS WILL END THE THUNDERSTORM THREAT BUT ALSO
DEEPEN THE MARINE LAYER. HIGH PRESSURE WILL REBUILD OVER THE AREA
FRIDAY AND SATURDAY.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
.TODAY THROUGH WEDNESDAY NIGHT...MODELS WERE CORRECT IN SHOWING AIR
MASS MORE MOIST AND UNSTABLE TODAY. 24 HOUR TEMP CHANGE SHOWS 1 TO 3
DEGREES CELSIUS COOLING ABOVE 500 MB ON MIRAMAR SOUNDING. BOTH IT
AND THE MORNING SOUNDING FROM YUMA SHOW PRECIPITABLE WATER VALUES
NEAR 1.8 INCHES AND SOUTHEAST FLOW THROUGH 25000 FT. DEWPOINTS
ACROSS THE ANZA BORREGO DESERT AND COACHELLA VALLEY ARE UP 10 TO 15
DEGREES...RANGING IN THE UPPER 60S TO UPPER 70S...AND UP A COUPLE
DEGREES ACROSS THE DESERT SLOPES OF THE MOUNTAINS. THE 12Z STANDARD
LEVEL ANALYSES SHOW THE MID/UPPER LEVEL RIDGE HAS SHIFTED
EAST/ERODED OVER NORTHERN BAJA CALIFORNIA/SW CALIFORNIA. SO THE DOOR
IS WIDE OPEN AND THE TROUGH OFF THE CENTRAL CALIFORNIA COAST ALONG
120W WILL PROVIDE THE DRAW FOR ADDITIONAL MONSOON MOISTURE TO SURGE
ACROSS THE FORECAST AREA THROUGH AT LEAST TONIGHT. THE NEXT ADJACENT
UPSTREAM SOUNDING...GUAYMAS MEXICO...SHOWS PRECIPITABLE WATER AT
2.44 INCHES. THE MODELS MOVE THE TROUGH SLOWLY EAST TO THE CENTRAL
CALIFORNIA COAST WEDNESDAY MORNING AND TO SOUTHERN NEVADA/SOUTHEAST
CALIFORNIA THURSDAY MORNING. THIS TIMING AND MOVEMENT BRINGS A
THREAT OF ELEVATED/NOCTURNAL CONVECTION TO ALL AREAS TONIGHT INTO
WEDNESDAY NIGHT. HAVE ALREADY UPDATES GRIDS AND ZONE FORECASTS TO
REFLECT THIS.
.THURSDAY THROUGH TUESDAY AUGUST 28...DISCOUNTING THE GFS SOLUTION
OF A FOUR CORNERS HIGH REDEVELOPING NEXT WEEK. CONSENSUS OF MODELS
SHOW HIGH PRESSURE RIDGE REBUILDS ACROSS THE AREA THROUGH SATURDAY
THEN SHIFTS EASTWARD SUNDAY AND MONDAY WITH THE RIDGE BEING
FLATTENED ON TUESDAY AS ZONAL FLOW/STORM TRACK DEVELOPS ALONG 40N
LATITUDE. FOR SW CALIFORNIA THIS SHOULD YIELD A WARMING AND DRYING
TREND THROUGH SATURDAY WITH A LOWERING MARINE LAYER...THEN A SLIGHT
COOLING TREND WITH DEEPER MARINE LAYER AND GUSTY SOUTHWEST WINDS
THROUGH TUESDAY.
&&
.AVIATION...
211530Z...COAST/VALLEYS...STRATUS...WITH BASES AROUND 1000 FT MSL
AND TOPS NEAR 1800 FT MSL...SHOULD CLEAR TOWARDS THE COAST THIS
MORNING...WITH VFR CONDS EXPECTED BTWN 16-17Z. HOWEVER...CIGS ARE
HAVING DIFFICULTY CLEARING SO FAR TODAY...CREATING A SMALL
POSSIBILITY OF THE COAST NOT CLEARING BY 17Z AND LINGERING THERE
THROUGHOUT THE DAY. STRATUS...WITH SLIGHTLY HIGHER TOPS AND
BASES...WILL RETURN TO THE COAST TONIGHT BTWN 03-06Z AND WILL PUSH
AROUND 20 SM INLAND BY MID WED MORNING. CLEARING OF STRATUS WED
MORNING MAY BE DIFFICULT...AND THE POSSIBILITY OF STRATUS HUGGING
THE COAST THROUGHOUT THE DAY ON WED EXISTS.
MTNS/DESERTS...CLEAR SKIES WITH UNRESTRICTED VIS TIL 19Z THIS
AFTN...THEN SCT-BKN CLOUDS LAYERED FROM 10K FT TO 40K FT WITH
ISOLATED/SCATTERED SHOWERS AND TSTMS POSSIBLE THROUGH THE REMAINDER
OF THE TAF PERIOD. TSTMS MAY PRODUCE STRONG UP/DOWNDRAFTS...GUSTY
SURFACE WINDS AND LOWERED VIS. AWAY FROM SHOWERS/TSTMS...VFR CONDS
FORECAST THROUGH THE TAF PERIOD.
&&
.FIRE WEATHER...
FROM CONFERENCE CALL THIS MORNING WITH GACC SOUTH OPS PSU...WFO
OXNARD...AND PARTICIPATING FIRE AGENCIES...DISCUSSED DRY LIGHTNING
THREAT/NOCTURNAL CONVECTION ASSOCIATED WITH THE LOW MOVING ACROSS
SOUTH CENTRAL CALIFORNIA TONIGHT THROUGH EARLY THURSDAY...HAVE BEEN
GETTING AND SHOULD CONTINUE TO HAVE ENOUGH HUMIDITY RECOVERY ACROSS
COASTAL/INLAND VALLEYS OF ORANGE/SAN DIEGO AND MOST OF INLAND EMPIRE
TO SLOW FIRE GROWTH. ONLY AREA OF CONCERN WOULD BE ALONG AND WEST OF
THE INTERSTATE 15 CORRIDOR FROM FOOTHILLS OF THE SAN GABRIEL MTNS
MOUNTAINS TO VICTORVILLE...WHERE WETTING RAINS WILL BE LESS LIKELY
TO ACCOMPANY THUNDERSTORMS.
&&
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...FLASH FLOOD WATCH UNTIL 8 PM PDT THIS EVENING FOR THE APPLE AND
LUCERNE VALLEYS...COACHELLA VALLEY...RIVERSIDE COUNTY
MOUNTAINS...SAN BERNARDINO COUNTY MOUNTAINS...SAN DIEGO
COUNTY DESERTS...SAN DIEGO COUNTY MOUNTAINS.
PZ...NONE.
&&
PUBLIC/FIRE WEATHER...BALFOUR
SHORT TERM WARNINGS...HARRISON
AVIATION/MARINE...JJTHAZARDOUS WEATHER OUTLOOK...CORRECTION NATIONAL WEATHER SERVICE SAN DIEGO CA 1025 AM PDT TUE AUG 21 2012 CAZ055-056-058-060>062-220100- SAN BERNARDINO COUNTY MOUNTAINS-RIVERSIDE COUNTY MOUNTAINS- SAN DIEGO COUNTY MOUNTAINS-APPLE AND LUCERNE VALLEYS- COACHELLA VALLEY-SAN DIEGO COUNTY DESERTS- 1025 AM PDT TUE AUG 21 2012 ...FLASH FLOOD WATCH IN EFFECT THROUGH THIS EVENING... THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EXTREME SOUTHWESTERN CALIFORNIA. .DAY ONE...TODAY AND TONIGHT THUNDERSTORMS WITH HEAVY DOWNPOURS ARE POSSIBLE TODAY. THERE IS A SLIGHT CHANCE THAT THUNDERSTORMS MAY CONTINUE OVERNIGHT...MAINLY ACROSS THE SAN BERNARDINO COUNTY MOUNTAINS AND DESERTS. THE FLASH FLOOD POTENTIAL IS MODERATE TO HIGH. FLASH FLOODING IS POSSIBLE THROUGH THIS EVENING. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY THUNDERSTORMS ARE POSSIBLE THROUGH LATE WEDNESDAY AFTERNOON. FOR THURSDAY THROUGH MONDAY...NO SIGNIFICANT WEATHER IS EXPECTED. .SPOTTER INFORMATION STATEMENT... SKYWARN WEATHER ACTIVATION IS REQUESTED FOR SAN BERNARDINO COUNTY...RIVERSIDE COUNTY...AND SAN DIEGO COUNTY ACROSS THE MOUNTAINS AND DESERT AREAS. CAZ042-043-048-050-057-220100- ORANGE COUNTY COASTAL AREAS-SAN DIEGO COUNTY COASTAL AREAS- SAN BERNARDINO AND RIVERSIDE COUNTY VALLEYS-THE INLAND EMPIRE- SAN DIEGO COUNTY VALLEYS-SANTA ANA MOUNTAINS AND FOOTHILLS- 748 AM PDT TUE AUG 21 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EXTREME SOUTHWESTERN CALIFORNIA. .DAY ONE...TODAY AND TONIGHT... THERE IS A SLIGHT CHANCE OF THUNDERSTORMS LATE THIS AFTERNOON AND TONIGHT. THE FLASH FLOOD POTENTIAL IS LOW. HOWEVER BRIEF HEAVY DOWNPOURS ARE POSSIBLE AND MAY LEAD TO MINOR FLOODING OF LOW LYING URBAN AREAS. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY THERE IS A SLIGHT CHANCE OF THUNDERSTORMS WEDNESDAY. FOR THURSDAY THROUGH MONDAY...NO HAZARDOUS WEATHER IS EXPECTED. .SPOTTER INFORMATION STATEMENT... SKYWARN WEATHER ACTIVATION IS NOT REQUESTED AT THIS TIME...HOWEVER SPOTTERS ARE ENCOURAGED TO REPORT ANY SIGNIFICANT WEATHER. BALFOUR
The national radar mosaic for the moment the first event began.
2 flood. Local standard time, as filed.
A spotter reported 2 to 3 inches of water flowing along part of Route 78 and County Road S3 (San Felipe Road). |A Borrego County Road Maintenance crew also reported water and debris flowing across San Felipe Road just north of Highway 78 between mile markers 12 and 14.
California Highway Patrol reported roadway flooding along county highway 22 (Borrego Salton Sea Way).
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, August 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: 407762, 407764.