A series of shortwaves rotated around an upper-level low pressure system off the southern California coast on the 10th and 13th. This low provided the dynamics and moisture needed to set off elevated convection in Orange County on the 10th causing large hail, as well as other portions of the northern CWA which received heavy rain, flooding, hail and vast amounts of lightning on both days.
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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.
A series of shortwaves rotated around an upper-level low pressure system off the southern California coast on the 10th and 13th. This low provided the dynamics and moisture needed to set off elevated convection in Orange County on the 10th causing large hail, as well as other portions of the northern CWA which received heavy rain, flooding, hail and vast amounts of lightning on both days. Numerous hail reports of pea-sized to half-inch were reported on both days, though none of these caused damage. Several small lightning-sparked fires occurred with these storms as well.
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 10, 3:15 AM PST, 2 hours 15 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN DIEGO CA 415 AM PDT SAT SEP 10 2011 .SYNOPSIS... LOW PRESSURE CENTERED NEAR POINT CONCEPTION WILL CONTINUE COOLER WEATHER AND A DEEPER MARINE LAYER INTO EARLY NEXT WEEK. MID LEVEL MOISTURE AND INSTABILITY WILL BRING SCATTERED THUNDERSTORMS THROUGH THIS EVENING WITH FREQUENT LIGHTNING STRIKES AND THE POTENTIAL FOR STRONG GUSTY WINDS AND HAIL. CHANCES FOR MAINLY AFTERNOON AND EVENING THUNDERSTORMS MAINLY IN THE MOUNTAINS AND DESERTS WILL CONTINUE INTO AT LEAST EARLY NEXT WEEK. SOME DRYING IS POSSIBLE TOWARD THE END OF NEXT WEEK AS THE TROUGH OF LOW PRESSURE MOVES TO THE EAST. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .SHORT TERM (TODAY THROUGH MONDAY)... UPPER LEVEL LOW PRESSURE CENTERED NEAR POINT CONCEPTION WILL BRING COOLER WEATHER AND A DEEPER MARINE LAYER THROUGH MONDAY. MUCAPES AND MIDLEVEL INSTABILITY SHOWN BY THE NAM ARE QUITE IMPRESSIVE FOR TODAY. CONCUR WITH THE DISCUSSION FROM SPC ABOUT THE POTENTIAL FOR DAMAGING MICROBURSTS AND MARGINALLY SEVERE HAIL FOR THIS AFTERNOON AND EARLY EVENING. NAM BUFR SOUNDINGS ALSO SHOW PW'S INCREASING TO AROUND 1.7 INCH THIS AFTERNOON. COMBINED WITH THE STEERING LEVELS WINDS...THIS IS MARGINAL FOR FLASH FLOODING...BUT CANNOT RULE OUT LOCALLY HEAVY RAINFALL FOR SOME LOCATIONS. AFTER THIS EVENING...THE FOCUS FOR CONVECTION SHIFTS BACK TO THE NORTHERN MOUNTAIN AND DESERT AREAS AND MAINLY FOR THE AFTERNOONS AND EARLY EVENINGS. && .LONG TERM (TUESDAY THROUGH FRIDAY)... UPPER LEVEL LOW PRESSURE WILL REMAIN IN THE VICINITY OF SOUTHERN CALIFORNIA WITH SOME DIFFERENCES IN MODEL PLACEMENT. THIS SHOULD KEEP TEMPERATURES BELOW AVERAGE WITH SOME DISRUPTION TO THE NIGHT AND MORNING COASTAL STRATUS FIELD POSSIBLE AT TIMES. DEPENDING UPON THE PLACEMENT OF THE UPPER CENTER...THERE COULD BE ENOUGH RESIDUAL MOISTURE TO SUPPORT A CONTINUING CHANCE OF MAINLY AFTERNOON AND EARLY EVENING THUNDERSTORMS MAINLY IN THE MOUNTAINS AND DESERTS THROUGH AT LEAST MID WEEK. SOME DRYING IS POSSIBLE TOWARDS THE END OF THE WEEK AS THE TROUGH AXIS SHIFTS TOWARD THE EAST. && .AVIATION... 101000Z...COASTAL AREAS/INLAND VALLEYS...MARINE LAYER STRATUS WITH BASES OF FL016-019 AND TOPS OF FL025 HAS SPREAD 30-40 MI INLAND AFFECTING ALL COASTAL TERMINALS AND KONT. MARINE STRATUS IS EXPECTED TO SCATTER OUT BY 16-18Z...BUT WILL REMAIN ALONG THE BEACHES. MARINE LAYER STRATUS WILL RETURN TO THE COASTAL AIRPORTS AFTER 11/02Z. STRATUS IS EXPECTED TO SPREAD 30-40 MI INLAND IN SAN DIEGO COUNTY AND COVER ALL OF THE INLAND EMPIRE BY 11/09Z. MARINE LAYER STRATUS THIS EVENING WILL HAVE SLIGHTLY HIGHER BASES AND TOPS THAN THIS MORNING. SLIGHT CHANCE OF THUNDERSTORMS DURING TODAY WITH BASES OF FL090 AND TOPS TO FL450. GUSTY WINDS AND SMALL HAIL MAY ACCOMPANY THESE THUNDERSTORMS. MTNS/DESERTS...THUNDERSTORMS HAVE FORMED NEAR THE SOUTHERN PART OF THE COACHELLA VALLEY AND HAVE AFFECTED KTRM WITH OUTFLOW WINDS FROM THE SSE AND BASES AT FL090. THUNDERSTORM OUTFLOW WINDS MAY IMPACT KPSP THIS MORNING. THUNDERSTORMS ARE POSSIBLE THROUGHOUT THE DAY WITH BASES OF FL090 AND TOPS TO FL450. GUSTY WINDS AND SMALL HAIL MAY ACCOMPANY THESE THUNDERSTORMS ALONG WITH BLOWING DUST REDUCING VIS TO 2 SM. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && PUBLIC...MARTIN AVIATION/MARINE...MOKER NWS ON THE WEB AT WEATHER.GOV/SANDIEGO
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE SAN DIEGO CA 420 AM PDT SAT SEP 10 2011 CAZ042-043-048-050-055>058-060>062-110100- ORANGE COUNTY COASTAL AREAS-SAN DIEGO COUNTY COASTAL AREAS- SAN BERNARDINO AND RIVERSIDE COUNTY VALLEYS-THE INLAND EMPIRE- SAN DIEGO COUNTY VALLEYS-SAN BERNARDINO COUNTY MOUNTAINS- RIVERSIDE COUNTY MOUNTAINS-SANTA ANA MOUNTAINS AND FOOTHILLS- SAN DIEGO COUNTY MOUNTAINS-APPLE AND LUCERNE VALLEYS- COACHELLA VALLEY-SAN DIEGO COUNTY DESERTS- 420 AM PDT SAT SEP 10 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR ALL OF EXTREME SOUTHWESTERN CALIFORNIA. .DAY ONE...TODAY AND TONIGHT NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY SCATTERED THUNDERSTORMS ARE EXPECTED THROUGH THIS EVENING. SOME MAY HAVE STRONG GUSTY WINDS AND HAIL. THE FLASH FLOOD POTENTIAL INDEX IS MODERATE...THUNDERSTORMS ARE EXPECTED TO DEVELOP AND ISOLATED FLASH FLOODING IS POSSIBLE. FOR SUNDAY...THERE IS A CHANCE OF MAINLY AFTERNOON AND EARLY EVENING THUNDERSTORMS...MAINLY IN THE MOUNTAINS AND DESERTS. THE FLASH FLOOD POTENTIAL INDEX IS LOW...THE RISK OF FLASH FLOODING IS MINIMAL. A SLIGHT CHANCE OF MAINLY AFTERNOON AND EARLY EVENING THUNDERSTORMS...MAINLY IN THE MOUNTAINS AND DESERTS...MAY CONTINUE INTO THE MIDDLE OF NEXT WEEK. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED FROM LATE MORNING THROUGH MID EVENING. MARTIN
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE SAN DIEGO CA
340 AM PDT SAT SEP 10 2011
CAZ055-060-101130-
SAN BERNARDINO COUNTY MOUNTAINS-
APPLE AND LUCERNE VALLEYS-
340 AM PDT SAT SEP 10 2011
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHERN SAN BERNARDINO COUNTY
UNTIL 430 AM PDT...
AT 330 AM PDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING
STRONG THUNDERSTORMS 9 MILES NORTH OF MORONGO VALLEY MOVING NORTH
AT 10 MPH.
HALF INCH HAIL AND WIND GUSTS TO 40 MPH ARE POSSIBLE WITH THESE
STORMS...ALONG WITH BRIEF HEAVY RAIN AND FREQUENT DANGEROUS
LIGHTNING.
AREAS AFFECTED BY THIS STORM INCLUDE...JOHNSON VALLEY.
LAT...LON 3446 11641 3436 11641 3432 11647 3426 11644
3418 11644 3416 11646 3410 11660 3439 11676
3443 11661
TIME...MOT...LOC 1037Z 152DEG 7KT 3420 11658The Santa Ana Mts radar (KSOX), 39 km away, was scanning. The volume nearest the first event began at 13:28 UTC.
3 flash flood, 2 hail, 1 funnel cloud. Local standard time, as filed.
Two reports of quarter-sized hail in Dana Point around 0600 PST. Quarter-sized hail was also reported in Costa Mesa and two others of one-inch hail in Anaheim between about 0900 and 0930 PST on the 10th.
Highway 18 was closed at Bear Valley Road just east of Apple Valley due to 1-2 feet of water on the roadway between mile marker 80 and High Road. Numerous vehicles were stalled due to water intake.
A spotter also reported 4 to 5 inches of standing water on highway 18 between Dead Man's Point and Highway 247. Multiple vehicles were also stalled here due to water intake.
Hail of dime size or 3/4 inch was reported with heavy rain in both Big Bear City and Highland from a cluster of thunderstorms.
A thunderstorm trained over the area dropping moderate rain for approximately three hours. As a result, a channel overflowed, pushing 8 inches of mud onto SR 111 between Highway 195 and Mecca Avenue. The Palm Ditch Bridge was was covered in this mud, but was declared undamaged.
Numerous other roadways in the area were closed due to flooding and/or mud flows as well.
Heavy rain in the Pinion Hills/Antelope Valley Hills area caused flooding near Highway 138. Mud and rocks as large as oranges covered the roadway. In nearby Wrightwood, a spotter reported Sheep Creek crossing at Lone Pine Canyon Road was closed due to a flow of mud, rock and tree debris. The spotter reported a half of an inch of rainfall in 30 minutes.
Storm Chaser Will Wilkens captured a funnel cloud on video near Perris around 1440 PST. There was a strong thunderstorm in the area when the funnel was sighted.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2011Every state in 2011This day in weather historyWarnings in California, September 2011
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: 346456, 346460, 346462, 346465, 347019, 347023.