A slow moving upper level low brought periods of showers and isolated thunderstorms on the 6th and 7th, with the most widespread activity occurring on the 6th. The most persistent storm developed over Ontario, CA and was nearly stationary for 3 hours over the city.
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.
A slow moving upper level low brought periods of showers and isolated thunderstorms on the 6th and 7th, with the most widespread activity occurring on the 6th. The most persistent storm developed over Ontario, CA and was nearly stationary for 3 hours over the city.
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 May 6, 2:44 AM PST, 3 hours 46 minutes earlier.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
344 AM PDT FRI MAY 6 2016
.SYNOPSIS...
A SLOW MOVING LOW PRESSURE SYSTEM WILL BRING PERIODS OF SHOWERS
AND ISOLATED THUNDERSTORMS THROUGH EARLY EVENING...DECREASING
DURING THE WEEKEND. WARMER AND DRY FOR NEXT WEEK. THE MARINE LAYER
AND WEAK ONSHORE FLOW WILL KEEP COASTAL AREAS COOLER WITH AREAS OF
NIGHT AND MORNING LOW CLOUDS AND FOG. THE ONSHORE FLOW WILL ALSO
BRING GUSTY WEST WINDS TO THE MOUNTAINS AND DESERTS EACH LATE
AFTERNOON THROUGH LATE EVENING.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
.SHORT TERM (TODAY THROUGH SUNDAY)...
A SLOW MOVING CLOSED LOW PRESSURE SYSTEM CENTERED OVER SOUTHERN
CALIFORNIA WILL MOVE INTO THE CENTRAL ROCKIES THROUGH SUNDAY.
EARLY THIS MORNING...A SHORTWAVE OFF THE NORTHERN BAJA COAST WAS
ENHANCING SHOWERS OVER THE COASTAL WATERS AND ADJACENT COASTAL
AREAS OF NORTHERN BAJA AND FAR SOUTHERN CALIFORNIA...MAINLY
CENTRAL AND SOUTHERN PORTIONS OF COASTAL SAN DIEGO COUNTY.
OVERNIGHT THROUGH 3 AM...GREATEST RAINFALL AMOUNTS HAVE BEEN NEAR
THE COAST OF SAN DIEGO FROM JUST NORTH OF LA JOLLA TO AROUND DEL
MAR WITH ONE THIRD INCH OR MORE OF RAINFALL IN THESE AREAS WITH
THE GREATEST AMOUNT OF AROUND 0.6 INCH NEAR DEL MAR. FOR THE NEXT
FEW HOURS...THE MOST WIDESPREAD SHOWER COVERAGE IS EXPECTED OVER
CENTRAL AND SOUTHERN COASTAL AREAS OF SAN DIEGO COUNTY EXTENDING
INTO THE WESTERN VALLEYS. GIVEN THE RAINFALL THAT HAS ALREADY
OCCURRED...HEAVIER DOWNPOURS HAVE THE POTENTIAL TO CAUSE LOCAL
URBAN FLOODING...ESPECIALLY IN POORLY DRAINED AREAS.
FOR THIS AFTERNOON AND EARLY EVENING...THE HIGHER RESOLUTION
MODELS SHIFT THE GREATER SHOWER AND ISOLATED THUNDERSTORM
COVERAGE TO THE MOUNTAINS...DESERTS...AND INLAND VALLEYS WITH
GREATEST COVERAGE AND RAINFALL AMOUNTS OVER THE MOUNTAINS. A
FLASH FLOOD WATCH HAS BEEN ISSUED FOR THE MOUNTAINS AND DESERTS
FOR THIS AFTERNOON AND EARLY EVENING.
THE CHANCE OF SHOWERS AND SLIGHT CHANCE OF THUNDERSTORMS WILL
CONTINUE FOR SATURDAY AFTERNOON AND EARLY EVENING...MAINLY IN THE
MOUNTAINS...DESERTS...AND INLAND VALLEYS WITH A SLIGHT CHANCE OF
SHOWERS FOR THE MOUNTAINS SUNDAY AFTERNOON AND EARLY EVENING.
OTHERWISE...THERE WILL BE SCATTERED SHOWERS...MAINLY FOR
COASTAL...VALLEY...AND MOUNTAIN AREAS OF SAN DIEGO COUNTY FOR
TONIGHT INTO SATURDAY MORNING...WITH LESSER COVERAGE FOR SATURDAY
NIGHT INTO EARLY SUNDAY MORNING.
SNOW LEVELS WILL MOSTLY FLUCTUATE BETWEEN 6500 AND 7000 FEET WITH
SEVERAL INCHES OF SNOW POSSIBLE ABOVE 7500 FEET.
COOLER TEMPERATURES FOR TODAY WILL BEGIN TO SLOWLY WARM FOR
SATURDAY AND SUNDAY. GUSTY WEST WINDS IN THE MOUNTAINS AND DESERTS
OF RIVERSIDE AND SAN DIEGO COUNTIES WILL GRADUALLY WEAKEN THIS
MORNING.
&&
.LONG TERM (MONDAY THROUGH THURSDAY)...
HIGH PRESSURE ALOFT NEAR THE WEST COAST WILL BRING DRY AND WARMER
WEATHER INLAND AREAS. THE MARINE LAYER AND WEAK ONSHORE FLOW WILL
KEEP COASTAL AREAS COOLER WITH AREAS OF NIGHT AND MORNING LOW
CLOUDS AND FOG.
&&
.AVIATION...
060900Z...COASTS/VALLEYS...BKN-OVC LAYERS 2500-6000 FT MSL WITH -
SHRA AND ISOLATED TSRA THROUGH THIS EVENING. BASES LOCALLY LOWERING
TO AROUND 1500 FT WITH 2-4SM VIS IN HEAVIER SHOWERS. SHOWERS WILL
GRADUALLY TAPER OFF LATE THIS EVENING.
MOUNTAINS/DESERTS...SHOWERS AND ISOLATED THUNDERSTORMS CONTINUING TO
DEVELOP THIS MORNING AND INTO FRIDAY EVENING. VIS WILL BE REDUCED IN
HEAVIER SHOWERS AND COASTAL SLOPES OF THE MOUNTAINS WILL REMAIN
OBSCURED IN CLOUDS/PRECIP. SHOWERS WILL GRADUALLY TAPER OFF LATE
THIS EVENING.
&&
.MARINE...
200 AM...A PACIFIC STORM WILL BRING A SLIGHT CHANCE OF THUNDERSTORMS
THROUGH LATE THIS AFTERNOON. THESE STORMS COULD PRODUCE CLOUD TO
WATER LIGHTNING AND BRIEF GUSTY WINDS. OTHERWISE...NO HAZARDOUS
MARINE WEATHER IS EXPECTED SATURDAY THROUGH TUESDAY.
&&
.SKYWARN...
SKYWARN ACTIVATION MAY BEEN NEEDED FOR THE MOUNTAINS AND DESERTS
FOR THIS AFTERNOON AND EARLY EVENING. WEATHER SPOTTERS ARE
ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...WIND ADVISORY UNTIL 5 AM PDT EARLY THIS MORNING FOR RIVERSIDE
COUNTY MOUNTAINS-SAN DIEGO COUNTY DESERTS-SAN DIEGO COUNTY
MOUNTAINS-SAN GORGONIO PASS NEAR BANNING.
FLASH FLOOD WATCH FROM NOON PDT TODAY THROUGH THIS EVENING FOR
APPLE AND LUCERNE VALLEYS-COACHELLA VALLEY-RIVERSIDE COUNTY
MOUNTAINS-SAN BERNARDINO COUNTY MOUNTAINS-SAN DIEGO COUNTY
DESERTS-SAN DIEGO COUNTY MOUNTAINS-SAN GORGONIO PASS NEAR
BANNING.
PZ...NONE.
&&
PUBLIC...17
AVIATION/MARINE...TSThe San Diego radar (KNKX), 22 km away, was scanning. The volume nearest the first event began at 14:32 UTC.
4 flood, 2 flash flood, 1 heavy rain. Local standard time, as filed.
The Lomas Santa fe Drive off ramp from Interstate 5 was flooded.
One car was stranded in knee deep water near Airway Road and La Media.
CHP reported flooding with debris in the roadway at the 4th St. on ramp to Interstate 10.
Multiple cars were partially submerged at the intersection of Grove Ave. and E Francis St., resulting in the temporarily shut down of the intersection.
Street flooding reported at the intersection of Walnut St. and Cucamonga Ave.
CHP reported vehicles unable to move due to high water at the on ramp from Vineyard Ave. to State Route 60.
In Ontario a local business suffered a roof collapse in the 1700 block of S. Hellman Ave. due to heavy rain. Near by, Ontario International Airport reported rain rates as high as 2.7 inches per hour.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2016Every state in 2016This day in weather historyWarnings in California, May 2016
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: 635824, 635823, 635827, 635826, 635828, 635830, 635834.