Scattered thunderstorms produced heavy rain and severe wind gusts across the Inland Empire, mountains and deserts on Thursday, September 9, leading to flooding, debris flows and rock slides. Elevated convection also made it to the coast on September 9. On September 10, severe thunderstorms producing heavy rainfall impacted the lower deserts.

Thunderstorm Wind in SAN DIEGO, CALIFORNIA
From 10-SEP-21 14:20:00 to 10-SEP-21 14:20:00 (PST-8)
Location: BORREGO SPGS ARPT
Magnitude: 50.00 MG
Reported by: Mesonet

Mesonet station NRWSD Narrows Sub (SDGE) reported a wind gust to 50 knots along Highway 78. The temperature also dropped from 101 degrees to 74 degrees F.

Lightning in SAN BERNARDINO, CALIFORNIA
From 09-SEP-21 14:16:00 to 09-SEP-21 14:16:00 (PST-8)
Location: MENTONE
Property damage: 0.00K
Crop damage: 1.00K
Reported by: Department of Highways

The Department of Highways reported a tree was on fire after being struck by lightning.

High Wind in SAN BERNARDINO AND RIVERSIDE COUNTY VALLEYS - THE INLAND EMPIRE, CALIFORNIA
From 09-SEP-21 14:20:00 to 09-SEP-21 14:20:00 (PST-8)
Magnitude: 56.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Mesonet station SoCal Edison SCE038 Calimesa reported a thunderstorm wind gust to 65 mph. This occurred on Roberts Road.

Dust Storm in SAN DIEGO COUNTY DESERTS, CALIFORNIA
From 10-SEP-21 14:55:00 to 10-SEP-21 14:55:00 (PST-8)
Reported by: AWOS

AOWS station KL08 Borrego Valley Airport reported a 47 mph wind gust. Reduced visibility down to 0.75 mile in blowing dust.

Flood in SAN DIEGO, CALIFORNIA
From 10-SEP-21 14:30:00 to 10-SEP-21 14:30:00 (PST-8)
Location: BORREGO SPGS ARPT
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Department of Highways

The Department of Highways reported flooding and rocks State Highway Route 78 and Borrego Springs Road.

Flood in RIVERSIDE, CALIFORNIA
From 09-SEP-21 15:58:00 to 09-SEP-21 15:58:00 (PST-8)
Location: BANNING MUNI ARPT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Flooding reported on Ramsey St on ramp and I-10 East.

Lightning in SAN DIEGO, CALIFORNIA
From 09-SEP-21 17:00:00 to 09-SEP-21 21:00:00 (PST-8)
Location: LA JOLLA
Property damage: 0.00K
Crop damage: 10.00K
Reported by: Unknown

Widespread convection across the San Bernardino and Riverside County Mountains as well as coastal San Diego and Orange Counties. Earth Networks lightning strike data provided.

Debris Flow in SAN BERNARDINO, CALIFORNIA
From 09-SEP-21 14:15:00 to 09-SEP-21 14:15:00 (PST-8)
Location: BIG BEAR LAKE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 10.00K
Reported by: Law Enforcement

A debris flow was reported along Highway 18 due to heavy rain from thunderstorms. Radar estimated rainfall of 1 to 2 inches in 1 hour occurred on the steep slopes at the winding portion of Arctic Circle Highway 18. Rock slides were reported onto the highway. CHP closure on Highway 18.

Heavy Rain in RIVERSIDE, CALIFORNIA
From 09-SEP-21 16:00:00 to 09-SEP-21 16:00:00 (PST-8)
Location: WEST PALM SPGS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: County Official

Riverside County Flood Control reported that Lower Snow Creek received 1.10 inch of rain in 1 hour and 0.39 inch of rain in 15 minutes from a nearby thunderstorm.