A surge of monsoonal moisture brought scattered thunderstorms to the mountains and deserts. Some of the thunderstorms were strong, producing heavy rain and flash flooding across the deserts.
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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 LOX wrote it up.
A surge of monsoonal moisture brought scattered thunderstorms to the mountains and deserts. Some of the thunderstorms were strong, producing heavy rain and flash flooding across the deserts.
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 Los Angeles, CA wrote its last area forecast discussion before the first event at Sep 9, 12:55 PM PST, 3 hours 12 minutes earlier.
SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 155 PM PDT SUN SEP 9 2012 .SYNOPSIS... SCATTERED SHOWERS WILL LIKELY DEVELOP OVER THE LOS ANGELES AND VENTURA COUNTY MOUNTAINS AND ANTELOPE VALLEY THIS AFTERNOON...THEN POSSIBLY MOVE INTO SOME VALLEY AND INTERIOR COASTAL AREAS. A COOLING AND DRYING TREND IS EXPECTED MONDAY THROUGH TUESDAY...BUT ENOUGH MOISTURE MAY LINGER ON MONDAY FOR ISOLATED THUNDERSTORMS ACROSS THE MOUNTAINS AND DESERT. TEMPERATURES WILL LIKELY INCREASE TO NEAR TO ABOVE NORMAL BY MID TO LATE WEEK AS HIGH PRESSURE BECOMES ESTABLISHED. && .SHORT TERM (TONIGHT-WED)... MAIN FORECAST ISSUE IN THE SHORT TERM REMAINS THE THREAT OF THUNDERSTORMS. SEEING STORMS DEVELOP THIS AFTERNOON ACROSS NORTHERN VENTURA COUNTY MOUNTAINS AND OVER THE SAN GABRIEL MOUNTAINS. REPORTS OF 0.5 INCH/HOUR ACROSS THE LOCKWOOD VALLEY WHERE CELLS WERE NOT MOVING MUCH. IN LOS ANGELES COUNTY...STORMS HAVE NOT HELD TOGETHER VERY WELL THROUGH 21Z BUT THIS COULD CHANGE IN THE NEXT TWO HOURS DUE TO OUTFLOW BOUNDARIES FROM LARGER CELLS FROM THE EAST. BEST INSTABILITY AND LIFT WILL REMAIN OVER HIGHER TERRAIN AND DO NOT EXPECT MUCH THREAT TO MOVE INTO THE VALLEYS THIS EVENING. THERE REMAINS A POSSIBILITY OF STORMS THROUGHOUT THE NIGHT (ALTHOUGH LOW CONFIDENCE) DUE TO THE UPPER DISTURBANCE MOVING FROM EAST TO WEST AND TIED TO THE LOW PRESSURE SYSTEM ACROSS THE NORTHERN BAJA. HIGH PRESSURE RIDGE OVER THE CWA WILL CONTINUE BEING SQUEEZED BY THE DISTURBANCE TO THE SOUTH AND A WEAK UPPER TROUGH MOVING ACROSS NORTHERN CAL. OUR REGION REMAINS ON THE EDGE OF THE BEST MOISTURE THROUGH MONDAY EVENING. INSTABILITY PARAMETERS FOR MONDAY LOOK EVERY BIT AS GOOD AS TODAY AND STORM MOTION CONTINUES TO BE LESS THAN 5KTS. WILL SEE HOW TODAY PROGRESSES AND LET LATER SHIFTS DECIDE IF ANOTHER FLASH FLOOD WATCH WILL BE NEEDED FOR MONDAY. HEIGHTS BEGIN TO DECLINE TOMORROW...THEREFORE HIGH TEMPERATURES WILL BE SEVERAL DEGREES COOLER. IT REMAINS UNSTABLE OVER THE VENTURA/LOS ANGELES COUNTY MOUNTAINS ON TUESDAY AFTERNOON BUT MOISTURE DECREASES AS A WEAK UPPER TROUGH DROPS INTO THE REGION FROM THE NORTH. WILL KEEP THUNDERSTORM CHANCES JUST BELOW MENTION IN THE FORECAST FOR TUESDAY. TEMPERATURES CONTINUE TO SLIDE DOWNWARD THROUGH TUESDAY THEN START TO REBOUND ON WEDNESDAY AS THE HIGH PRESSURE RIDGE BUILDS ALONG THE WEST COAST. .LONG TERM (THU-SUN)... THE HIGH PRESSURE RIDGE AMPLIFIES NORTHWARD INTO THE PACIFIC NORTHWEST ON THURSDAY BEFORE BEGINNING TO BREAK DOWN LATE FRIDAY OR SATURDAY. OUR REGION SHOULD CONTINUE TO SEE WARM TEMPERATURES THROUGH SATURDAY WITH A VERY SHALLOW MARINE LAYER THAT COULD BRING PATCHY CLOUDS/FOG FOR AREA BEACHES. THERE ARE SOME MEDIUM RANGE MODEL DIFFERENCES NEXT WEEKEND AS THE PATTERN AMPLIFIES ACROSS NORTHERN LATITUDES. THE GENERAL TREND FOR SOUTHERN CAL IS LOWERING HEIGHTS AND ONSHORE FLOW AS A LOW PRESSURE TROUGH DEEPENS OVER THE NORTHERN ROCKIES. FOR NOW...KEPT THE FORECAST DRY BUT TRENDED COOLER FOR SUNDAY. && .AVIATION...09/0025Z...GENERALLY HI CONFIDENCE IN THE CURRENT TAFS...EXCEPT MODERATE CONFIDENCE FOR KSBP AND KSMX DUE TO UNCERTAINTIES WITH TIMING AND EXTENT OF ANY LOW CLOUDS AND FOG LATE TONIGHT INTO SUN MORNING. THERE IS A 20 PERCENT CHANCE THE LOW CLOUDS MAY NOT DEVELOP THERE ESPECIALLY AT KSBP. OTHERWISE GENERALLY VFR CONDITIONS CAN BE EXPECTED AT THE AIRFIELDS THRU SUN. THERE IS ALSO A SLIGHT CHANCE OF THUNDERSTORMS FOR MUCH OF VTU/L.A. COUNTIES ON SUN. ADDED A PROB30 GROUP FOR THUNDERSTORMS SUN AFTERNOON AT KPMD AND KWJF WITH GUSTY VARIABLE WINDS AND MVFR VSBYS IN ANY THUNDERSTORMS. KLAX...GENERALLY HI CONFIDENCE IN THE CURRENT TAF WITH VFR CONDITIONS THRU SUN EVENING. HOWEVER...THERE IS A 10-20 PERCENT CHANCE SCT-BKN LOW CLOUDS WITH IFR/MVFR CONDITIONS COULD AFFECT THE AIRFIELD LATE TONIGHT INTO SUN MORNING. ALSO...THERE IS A SLIGHT CHANCE OF THUNDERSTORMS SUN AFTERNOON AND EVENING WITH LOWERED VSBYS IN ANY THUNDERSTORMS. KBUR...HI CONFIDENCE IN CURRENT TAF WITH VFR CONDITIONS THROUGH SUN...ALTHO THERE IS A SLIGHT CHANCE OF THUNDERSTORMS SUN AFTERNOON WITH LOWERED VSBYS IN ANY THUNDERSTORMS. && .LOX WATCHES/WARNINGS/ADVISORIES... FLOOD WATCH (SEE LAXFFALOX). SMALL CRAFT ADVISORY (SEE LAXMWWLOX). && PUBLIC...BOLDT AVIATION...HALL SYNOPSIS...SWEET WWW.WEATHER.GOV/LOSANGELES
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 1030 AM PDT SUN SEP 9 2012 CAZ034>041-044>046-051>054-059-087-088-547-548-101300- SAN LUIS OBISPO COUNTY CENTRAL COAST- SANTA BARBARA COUNTY CENTRAL COAST-SANTA YNEZ VALLEY- SAN LUIS OBISPO COUNTY INTERIOR VALLEYS-CUYAMA VALLEY- SANTA BARBARA COUNTY SOUTH COAST-VENTURA COUNTY COAST- LOS ANGELES COUNTY COAST INCLUDING DOWNTOWN LOS ANGELES- VENTURA COUNTY INTERIOR VALLEYS-VENTURA COUNTY COASTAL VALLEYS- SANTA MONICA MOUNTAINS RECREATIONAL AREA- SAN LUIS OBISPO COUNTY MOUNTAINS- SANTA BARBARA COUNTY MOUNTAINS-VENTURA COUNTY MOUNTAINS- LOS ANGELES COUNTY MOUNTAINS EXCLUDING THE SANTA MONICA RANGE- ANTELOPE VALLEY-CATALINA ISLAND-SANTA CLARITA VALLEY- LOS ANGELES COUNTY SAN FERNANDO VALLEY- LOS ANGELES COUNTY SAN GABRIEL VALLEY- 1030 AM PDT SUN SEP 9 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHWESTERN CALIFORNIA. .DAY ONE... TODAY AND TONIGHT THERE IS A CHANCE OF THUNDERSTORMS IN THE ANTELOPE VALLEY AND THE MOUNTAINS OF VENTURA COUNTY THIS AFTERNOON INTO TONIGHT... WITH THUNDERSTORMS LIKELY IN THE MOUNTAINS OF LOS ANGELES COUNTY. SOME THUNDERSTORMS THIS AFTERNOON AND EVENING MAY PRODUCE VERY HEAVY RAINFALL AND FLASH FLOODING. A FLASH FLOOD WATCH IS IN EFFECT FOR THESE AREAS. LIGHTNING FROM ANY THUNDERSTORM MAY SPARK FIRES IN AREAS THAT DO NOT RECEIVE MUCH RAINFALL. * FLOOD WATCH................SEE WGUS66 KLOX - FFALOX FOR DETAILS * .DAYS TWO THROUGH SEVEN... MONDAY THROUGH SATURDAY THERE IS A CHANCE OF SHOWERS AND THUNDERSTORMS IN THE MOUNTAINS OF LOS ANGELES AND VENTURA COUNTIES AND THE ANTELOPE VALLEY MONDAY AFTERNOON AND EVENING. BRIEFLY HEAVY DOWNPOURS AND GUSTY WINDS ARE POSSIBLE WITH ANY THUNDERSTORM. LIGHTNING FROM ANY THUNDERSTORM MAY SPARK FIRES IN AREAS THAT DO NOT RECEIVE MUCH RAINFALL. .SPOTTER INFORMATION STATEMENT... WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES. DB/ASR/EB
The national radar mosaic for the moment the first event began.
2 flash flood. Local standard time, as filed.
Scattered strong thunderstorms developed over the deserts of Los Angeles county. Local law enforcement reported flash flooding southeast of the community of Pearblossom due to heavy thunderstorm rain.
Scattered strong thunderstorms developed over the deserts of Los Angeles county. Local law enforcement reported flash flooding between Pearblossom and Lake Los Angeles, near the intersection of 220th Street East and Palmdale Boulevard.
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: 413934, 413935.