Flash Flood in California, September 5, 2003

Name: Flash Flood in California, September 5, 2003
Start: 2003-09-05T12:35
End: 2003-09-05T13:15
Location: California

September 5, 2003 · NWS SGX · 1 event in 1 county or zone

5 inches of rain fell in 65 minutes. 5 inch diameter hail was also observed.

Where it happened

Every event with a place to put it; 1 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: $20,000
Crop damage: None recorded
Events: 1

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.

What happened

The episode as NWS SGX wrote it up.

Extensive flooding was reported in and around Anza after 2.5 inches of rain fell in 65 minutes. Wind gusts were measured at 50 mph, and 0.5 inch diameter hail was also observed.

What forecasters said that day

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 5, 8:30 AM PST, 4 hours 5 minutes earlier.

Area forecast discussion, Sep 5, 8:30 AM PST, 4 hours 5 minutes before

EXTREME SOUTHWESTERN CALIFORNIA AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE SAN DIEGO CALIFORNIA
930 AM PDT FRI SEP 5 2003

.SYNOPSIS...FLASH FLOOD WATCH FOR THE MOUNTAINS AND DESERTS FROM NOON
UNTIL 700 PM TODAY. MOISTURE IN SOUTH FLOW ALOFT WILL BRING A CHANCE
OF SHOWERS AND THUNDERSTORMS TO THE MOUNTAINS AND DESERTS THIS
AFTERNOON...DECREASING SATURDAY AFTERNOON. OTHERWISE...FAIR UNDER
WEAKENING HIGH PRESSURE. UPPER LEVEL LOW PRESSURE MOVING PAST TO THE
NORTH WILL BRING A DEEPER MARINE LAYER AND COOLING EARLY NEXT WEEK.
WARMER AGAIN TOWARD THE SECOND HALF OF NEXT WEEK AS HIGH PRESSURE
BUILDS OFF THE COAST.

.DISCUSSION...UPDATED FORECAST MAINLY FOR TEMPERATURES THAT ARE
RUNNING HIGHER SO FAR TODAY. OFFSHORE TREND YESTERDAY HAS RESULTED
IN A WARM MORNING...AND CLEAR SKIES MAXIMIZING THE SUN POTENTIAL.
THE REST OF THE DISCUSSION IS THE SAME AS THE 630 AM ISSUANCE.

WEAK OFFSHORE GRADIENTS FROM THE NE AND WEAK ONSHORE TO THE E. THE
12Z NKX SOUNDING WAS QUITE WET AND UNSTABLE SO ISSUED A FLASH FLOOD
WATCH FOR THE MOUNTAINS AND DESERTS.

PLENTY OF MOISTURE TODAY FOR AFTERNOON THUNDERSTORMS...MAINLY IN THE
MOUNTAINS AND DESERTS. A FEW THUNDERSTORMS COULD FORM OVER THE INLAND
VALLEYS. OTHERWISE...GRADUALLY WEAKENING HI ALOFT WITH WEAK SLY FLOW
AND GENERALLY DECREASING MOISTURE THROUGH THE MID LEVELS TONIGHT AND
SAT. SMALLER CHANCE OF THUNDERSTORMS IN THE MOUNTAINS SAT. DRIER SW
FLOW ALOFT SUN FOR AN END TO THE MONSOONAL THUNDERSTORMS FOR A WHILE.
AN UPPER TROUGH MOVES INTO THE PAC NW SUN. OUR LOCAL HEIGHTS START TO
LOWER AND ONSHORE FLOW INCREASES SUN. THE MARINE LAYER WILL DEEPEN
AND BECOME MORE EXTENSIVE. THIS WILL BRING COOLING TO MOST
AREAS...ESPECIALLY W OF THE MOUNTAINS.

LONGER RANGE PROGS INDICATE THE TROUGH WILL MOVE PAST TO THE N MON
AND TUE FOR A CONTINUED COOLING TREND AND DEEPENING MARINE LAYER.
HEIGHTS RECOVER A LITTLE WED AND THU AS A RIDGE BUILDS ALONG THE
COAST FOR A DECREASING MARINE LAYER AND WARMING TREND.

SAN...FLASH FLOOD WATCH...SEE LAXFFASGX.

Hazardous weather outlook, Sep 5, 5:30 AM PST, 7 hours 5 minutes before

CAZ042-043-048-050-055>058-060>062-061300-

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE SAN DIEGO CA
630 AM PDT FRI SEP 5 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR
EXTREME SOUTHWESTERN CALIFORNIA.

.DAY ONE... TODAY THROUGH TONIGHT

FLASH FLOOD WATCH FOR THE HIGHER MOUNTAINS AND THE DESERTS FROM NOON
UNTIL 700 PM TODAY.

REFER TO LAXFFASGX WGUS66 KSGX FOR DETAILS.

.DAYS TWO THROUGH SEVEN... SATURDAY THROUGH THURSDAY

SLIGHT CHANCE OF THUNDERSTORMS IN THE MOUNTAINS AND DESERTS SATURDAY
AFTERNOON. OTHERWISE...NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SKYWARN ACTIVATION MAY BE REQUIRED TODAY AND TONIGHT.

The radar

The San Diego radar (KNKX), 134 km away, was scanning. The volume nearest the first event began at 20:37 UTC.

Open the radar archive at this moment

Event by event

1 flash flood. Local standard time, as filed.

Flash Flood, Riverside

When: September 5, 12:35 PM PST to 1:15 PM PST
Where: Riverside County, Anza
Property damage: $20,000
Reported by: TRAINED SPOTTER
Coordinates: 33.744, -115.994 (the zone’s center; the record gives no point)

What these are

Flash Flood: Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in California in 2003 Every state in 2003 This day in weather history Warnings in California, September 2003

Sources

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: 5337808.