A strong upper-level low pressure system dug south along the West Coast, moving inland directly over southern California. A vorticity maximum rotating around the low, along with the setup of a California Bight Coastal Convergence Zone (between drainage winds off the land and onshore flow from the low) created the perfect conditions for showers, thunderstorms and funnel clouds. The cold air instability and warm waters resulted in waterspouts and ocean-effect instability showers over the coastal waters and locally onshore during the morning hours. Showers and thunderstorms formed inland from afternoon heating as the low moved onshore, resulting in urban flooding in areas of the Inland Empire. The heaviest amounts ranged from three quarters of an inch to one inch, with other nearby areas receiving one-tenth of an inch to a half of an inch. Impacts included numerous street closures and 10 homes with either external or internal water damage in the Riverside, Colton and Fontana areas. Highway 52 at Interstate 15 in San Diego County was also closed for an hour due to flooding and multiple accidents.
Cold-air instability continued on the 12th, producing several more waterspouts off the Orange County coast.

Flood in RIVERSIDE, CALIFORNIA
From 11-OCT-12 16:00:00 to 11-OCT-12 18:00:00 (PST-8)
Location: GLEN AVON
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Several streets were flooded due to heavy rain, stranding motorists in their vehicles. Streets affected included Wineville Avenue, Limonite Avenue, 50th Street, Ben Nevis Blvc, Quartz Canyon Road, Fircrest Lane, Agate Street, Mission Blvd, Hastings Blvd, Fleming Street, Glen Street and Villa Woods Drive in Jurupa Valley. No one was injured.

Flood in RIVERSIDE, CALIFORNIA
From 11-OCT-12 16:00:00 to 11-OCT-12 18:00:00 (PST-8)
Location: NORCO
Flood cause: Heavy Rain
Property damage: 60.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Two homes on Crestview Drive between Mount Shasta and Mount Rushmore Drives sustained damage to the insides of the residences. Eight additional homes on the block sustained damage on the external portion. No injuries and no residents displaced.

Flood in SAN BERNARDINO, CALIFORNIA
From 11-OCT-12 17:00:00 to 11-OCT-12 18:00:00 (PST-8)
Location: COLTON ARPT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Street flooding occurred in Colton Valley between Hermosa and Grand Roads. Roadways were closed in that area.

Flood in SAN DIEGO, CALIFORNIA
From 12-OCT-12 05:00:00 to 12-OCT-12 07:00:00 (PST-8)
Location: CAMP ELLIOT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

City of San Diego reported the on ramp for highway 52 and from I -15 was closed in the morning for an hour due to flooded streets and multiple accidents.

Heavy Rain in SAN BERNARDINO, CALIFORNIA
From 11-OCT-12 15:30:00 to 11-OCT-12 16:30:00 (PST-8)
Location: FONTANA
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

A warehouse roof collapsed on the 11000 block of Mulberry Avenue in Fontana due to accumulation of over 1 foot of water. Drains were plugged allowing the water to accumulate. An alert gauge approximately 2 miles north of the location reported 1.02 inches of rain in 25 minutes between 1545 and 1610 PST.