A low pressure system from the East brought a surge of subtropical monsoon moisture into the region. These ingredients set off periods of showers and thunderstorms, with areas of flash flooding affecting the San Diego, Riverside and San Bernardino County mountains, as well as the high desert on the 21st and 22nd, including significant rainfall and flash flooding the morning of the 21st, resulting from a nocturnal MCS. Rainfall amounts varied widely, though some of the stronger storms produced very heavy rain of 2-3 inches at a time. This heavy rain combined with recent burn areas on the 21st to produce major debris flows, most notably at the Mountain Fire in Riverside County, near Idyllwild. Several locations within this burn area reported rock and debris flows across roadways, including Highway 74. One debris flow even tore through a pond, displacing the water and killing the fish. Portions of the Sunrise Highway and Interstate 8 in the San Diego County mountains and roadways in Ocotillo Wells were closed due to large amounts of flowing water, mud and rocks. The bulk of the storms on the 22nd affected the San Bernardino County mountains, especially the Big Bear area, where three homes were flooded. Another area of Big Bear was blanketed with up to 1.5 inches of accumulated hail, ranging from one-quarter to one-half inch in size, shredding some plants and flowers. The Anza Borrego State Park, in the San Diego County deserts, experienced the worst flash flooding on the 22nd. Dual-Pol radar reported estimates of 2 to 4 inches of rainfall within portions of the park. Several locations along Highway 78, through the park, had water, mud and rocks flowing over the road, the deepest of which was 12 inches deep and about 30 feet across. No one could pass through, stranding one car between this flow and another about 6 inches deep. The Fish Creek drainage within the park also experienced flash flooding, carrying away and destroying 3 unoccupied vehicles.

Flash Flood in SAN DIEGO, CALIFORNIA
From 21-JUL-13 13:00:00 to 21-JUL-13 15:00:00 (PST-8)
Location: PINE VLY
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Around 1315 PST, a spotter reported 6 inches of water flowing across Interstate 8 at the Pine Valley Road exit.

Debris Flow in SAN DIEGO, CALIFORNIA
From 21-JUL-13 13:00:00 to 21-JUL-13 14:00:00 (PST-8)
Location: BANNER
Flood cause: Heavy Rain / Burn Area
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

A Cleveland National Forest Battalion Chief reported 6 inches of mud and rocks flowing across Sunrise Highway (S1), just north of Shrine Camp. The Shrine Camp area was recently burned during the Chariot Fire. The nearby Volcan Mountain Alert gauge reported 0.78 inches of rain in 10 minutes and 1.14 inches of rain over 20 minutes.

Flash Flood in SAN DIEGO, CALIFORNIA
From 22-JUL-13 15:00:00 to 22-JUL-13 17:00:00 (PST-8)
Location: BORREGO SPGS ARPT
Flood cause: Heavy Rain
Property damage: 90.00K
Crop damage: 0.00K
Reported by: Park/Forest Service

Heavy rain over the Anza Borrego State Park, including the headwaters of Fish Creek and Vallecito Creek, caused severe flash flooding with debris in those creeks. Flood waters washed 3 vehicles far down the drainage of each of the creeks, destroying the vehicles. The Fish Creek drainage is actually an unmaintained state road, part of the State Park, with free public travel allowed, so this drainage is especially dangerous during heavy rain.

Flash Flood in RIVERSIDE, CALIFORNIA
From 21-JUL-13 02:30:00 to 21-JUL-13 04:30:00 (PST-8)
Location: ANZA
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Fire Dispatch for the Mountain Fire reported 1 foot of water crossing Morris Ranch Road near the fire. Dispatch also reported a rockslide and debris flow across Highway 74.

Flash Flood in RIVERSIDE, CALIFORNIA
From 21-JUL-13 11:00:00 to 21-JUL-13 14:00:00 (PST-8)
Location: THOUSAND PALMS
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

At 1129 PST, law enforcement reported 2 and a half feet of mud and water washing across Larsen Lane near the cross-section with Dillon road in Sky Valley. At 1350 PST, an 80-ft swath of dirt and rocks was in the roadway, The dirt was 3 feet thick with most rocks bigger than bowling balls. The road was closed due to it being impassable.

Hail in SAN BERNARDINO, CALIFORNIA
From 22-JUL-13 12:45:00 to 22-JUL-13 13:15:00 (PST-8)
Location: BIG BEAR CITY
Magnitude: 0.50 
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Public

A Big Bear resident reported that 0.5-inch hail had accumulated up to 1.5 inches deep in her yard. Plants and flowers in the yard were completely shredded by the hail.

Flash Flood in SAN BERNARDINO, CALIFORNIA
From 22-JUL-13 12:00:00 to 22-JUL-13 15:00:00 (PST-8)
Location: BIG BEAR LAKE
Flood cause: Heavy Rain
Property damage: 200.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Big Bear City Fire Department responded to three flooded homes within city limits. Other homeowners were able to divert the water from entering their homes. A spotter reported 2 to 3 inches of water running across Big Bear Boulevard near Greenway Drive. A Big Bear City resident reported a gauge total of 2.25 inches of rain.

Flash Flood in SAN DIEGO, CALIFORNIA
From 21-JUL-13 12:00:00 to 21-JUL-13 15:00:00 (PST-8)
Location: BANNER
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Highway 78 was flooded in two locations through Yaqui Pass with many large rocks in the roadway. Thirty vehicles were trapped between the two flooded locations, due to the road being impassable there. A weather service employee observed one of the flows was about 12 inches deep and another was about 6 inches deep.

Flash Flood in RIVERSIDE, CALIFORNIA
From 21-JUL-13 03:00:00 to 21-JUL-13 04:00:00 (PST-8)
Location: CATHEDRAL CITY
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Official NWS Observations

The stream gauge at Palm Canyon Creek reported a water rise of 1.5 feet in a normally dry creek bed around 315 PST. This gauge later measured a peak flow of 211 cfs at 1430 PST.

Flash Flood in SAN DIEGO, CALIFORNIA
From 21-JUL-13 12:00:00 to 21-JUL-13 13:30:00 (PST-8)
Location: DESERT LODGE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

California Highway Patrol closed Montezuma Valley Road at Mile Marker 14 because debris has made it impassable.

Flash Flood in RIVERSIDE, CALIFORNIA
From 21-JUL-13 12:00:00 to 21-JUL-13 15:00:00 (PST-8)
Location: MOUNTAIN CENTER
Flood cause: Heavy Rain / Burn Area
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Employee

Crews on the Mountain Fire reported 0.5 inches of rain in 30 minutes between 1258 and 1328 PST. A debris flow from the fire moved through a pond, displacing the water and killing the fish. Other crews reported 18 inches of water and mud across Apple Canyon Road near Highway 74.

Flash Flood in SAN DIEGO, CALIFORNIA
From 20-JUL-13 15:45:00 to 20-JUL-13 16:30:00 (PST-8)
Location: BOULDER OAKS
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Heavy rain was concentrated west of the Tecate Divide, along and a quarter mile on either side of Interstate 8. The rains were so heavy, they turned the rocky terrain in the distance into hundreds of small waterfalls and turned a local dirt road on an adjacent ranch site into a muddy flow.

Flash Flood in RIVERSIDE, CALIFORNIA
From 21-JUL-13 11:00:00 to 21-JUL-13 12:00:00 (PST-8)
Location: MECCA
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reports a hard closure of the intersection of Tyler Street and 64th Street in Mecca, due to roadway flooding. Intersection closed due to roads being impassable.