The month ended with one last major monsoon day. Convection developed rapidly and near the same time as an approaching short wave trough and daytime heating. Flash flooding was reported in many locations with several road closures in the Inland Empire, Victorville, Chihuahua Valley and the Coachella Valley (Cathedral City). Extensive damage was done by flood waters in Moreno Valley, Victorville and Cathedral City with a few high water rescues and residences and businesses inundated with mud and debris.

Flood in SAN BERNARDINO, CALIFORNIA
From 30-AUG-12 13:15:00 to 30-AUG-12 14:00:00 (PST-8)
Location: APPLE VLY
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter reported 0.75 inches of rain in 20 minutes, leading to urban flooding near the intersection of Central and Waalew in Apple Valley with an estimated 6 inches of water in the low sections of roadways.
Another spotter in nearby Lucerne Valley reported 1 to 2 inches of standing water along Highway 247 on the north side of town.

Flash Flood in SAN DIEGO, CALIFORNIA
From 30-AUG-12 13:00:00 to 30-AUG-12 13:45:00 (PST-8)
Location: DESCANSO
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A spotter estimated 2 to 3 feet of water flowing across Highway 79 a mile west of Chihuahua Valley Road. In addition, trees and branches 3 to 5 inches in diameter were floating across the roadway.

Flash Flood in RIVERSIDE, CALIFORNIA
From 30-AUG-12 13:00:00 to 30-AUG-12 15:00:00 (PST-8)
Location: CATHEDRAL CITY
Flood cause: Heavy Rain
Property damage: 150.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Major flash flooding in Cathedral City with 1 to 2 feet of rapidly moving water, closing several roads including East Palm Canyon (Highway 111) and Araby Drive. Water forced mud and debris into several businesses in town, causing significant damage.

Lightning in RIVERSIDE, CALIFORNIA
From 30-AUG-12 13:45:00 to 30-AUG-12 14:15:00 (PST-8)
Location: CATHEDRAL CITY
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter RIV230 reported heavy rain and lightning. Lightning struck a nearby palm tree, which then burst into flames. Winds also gusted to 25 mph.

Thunderstorm Wind in RIVERSIDE, CALIFORNIA
From 30-AUG-12 13:30:00 to 30-AUG-12 14:00:00 (PST-8)
Location: (RIV)RIVERSIDE ARPT
Magnitude: 53.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

The March AFB ASOS recorded a peak gust of 61 mph at 1347 PST. One of the planes at the museum was turned 180 degrees by the severe winds.
An Atmospheric Science teacher at nearby UC Riverside estimated wind gusts to 60 mph from a passing thunderstorm going through campus around the same time.

Flash Flood in SAN BERNARDINO, CALIFORNIA
From 30-AUG-12 15:00:00 to 30-AUG-12 16:00:00 (PST-8)
Location: THORN
Flood cause: Heavy Rain
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Heavy rain from thunderstorms just north of Victorville resulted in flooding on National Trails Highway at Lynhaven Lane and a swift water rescue of a van caught in 4 feet of moving water. Barbosa Road was also washed out.

Flood in RIVERSIDE, CALIFORNIA
From 30-AUG-12 15:00:00 to 30-AUG-12 16:00:00 (PST-8)
Location: ALBERHILL
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A spotter reported street flooding with water up to the curbs in some places at the north end of Lake Elsinore near Albert Hill.

Flash Flood in RIVERSIDE, CALIFORNIA
From 30-AUG-12 13:30:00 to 30-AUG-12 15:00:00 (PST-8)
Location: MORENO VALLEY
Flood cause: Heavy Rain
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Heavy rain caused flash flooding which closed San Timoteo Canyon Road. Six vehicles were stuck in the water. One person was rescued from a vehicle surrounded by a mud flow on San Timoteo Canyon Road and Live Oak Canyon Road. Rainfall of 1.53 inches fell in one hour at March AFB in Riverside.
Eastbound Highway 60 was closed at Redlands Boulevard due to flooding as well.
Mud and water also inundated a few homes in the Moreno Valley area.
At least 1 swift water rescue needed to be performed, including the one at Oliver Street and Cactus Avenue in Moreno Valley. Firefighters had to rescue persons trapped in their vehicle with water reported up to the windows.

Flash Flood in SAN DIEGO, CALIFORNIA
From 30-AUG-12 13:30:00 to 30-AUG-12 14:30:00 (PST-8)
Location: AGUA CALIENTE SPGS
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Employee

Heavy rain resulted in a debris flow on Highway 78 near Shelter Valley and Lizard Creek. A 2-foot boulder had to be removed from the roadway and one lane of the highway was closed.