A series of shortwaves rotated around an upper-level low pressure system off the southern California coast on the 10th and 13th. This low provided the dynamics and moisture needed to set off elevated convection in Orange County on the 10th causing large hail, as well as other portions of the northern CWA which received heavy rain, flooding, hail and vast amounts of lightning on both days. Numerous hail reports of pea-sized to half-inch were reported on both days, though none of these caused damage. Several small lightning-sparked fires occurred with these storms as well.

Funnel Cloud in RIVERSIDE, CALIFORNIA
From 13-SEP-11 14:15:00 to 13-SEP-11 15:00:00 (PST-8)
Location: PERRIS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Storm Chaser

Storm Chaser Will Wilkens captured a funnel cloud on video near Perris around 1440 PST. There was a strong thunderstorm in the area when the funnel was sighted.

Hail in ORANGE, CALIFORNIA
From 10-SEP-11 05:30:00 to 10-SEP-11 10:00:00 (PST-8)
Location: DANA PT
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Two reports of quarter-sized hail in Dana Point around 0600 PST. Quarter-sized hail was also reported in Costa Mesa and two others of one-inch hail in Anaheim between about 0900 and 0930 PST on the 10th.

Hail in SAN BERNARDINO, CALIFORNIA
From 13-SEP-11 03:00:00 to 13-SEP-11 06:00:00 (PST-8)
Location: BIG BEAR CITY
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail of dime size or 3/4 inch was reported with heavy rain in both Big Bear City and Highland from a cluster of thunderstorms.

Flash Flood in SAN BERNARDINO, CALIFORNIA
From 10-SEP-11 18:00:00 to 10-SEP-11 19:00:00 (PST-8)
Location: APPLE VLY ARPT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Highway 18 was closed at Bear Valley Road just east of Apple Valley due to 1-2 feet of water  on the roadway between mile marker 80 and High Road. Numerous vehicles were stalled due to water intake.
A spotter also reported 4 to 5 inches of standing water on highway 18 between Dead Man's Point and Highway 247. Multiple vehicles were also stalled here due to water intake.

Flash Flood in RIVERSIDE, CALIFORNIA
From 13-SEP-11 05:00:00 to 13-SEP-11 11:00:00 (PST-8)
Location: (TRM)THERMAL ARPT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

A thunderstorm trained over the area dropping moderate rain for approximately three hours. As a result, a channel overflowed, pushing 8 inches of mud onto SR 111 between Highway 195 and Mecca Avenue. The Palm Ditch Bridge was was covered in this mud, but was declared undamaged.
Numerous other roadways in the area were closed due to flooding and/or mud flows as well.

Flash Flood in SAN BERNARDINO, CALIFORNIA
From 13-SEP-11 12:00:00 to 13-SEP-11 15:00:00 (PST-8)
Location: SCOTLAND
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy rain in the Pinion Hills/Antelope Valley Hills area caused flooding near Highway 138. Mud and rocks as large as oranges covered the roadway. In nearby Wrightwood, a spotter reported Sheep Creek crossing at Lone Pine Canyon Road was closed due to a flow of mud, rock and tree debris. The spotter reported a half of an inch of rainfall in 30 minutes.