A line of elevated thunderstorms developed during the morning of the 20th over the ocean and along the coast ahead of an approaching upper-level low. Dynamic lift and monsoonal moisture led to further destabilization and increasing storm intensity with time. The initial band moved inland and organized thunderstorms with prolific lightning persisted over the Inland Empire and Riverside County mountains. The coastal and valley locations of San Diego and Riverside Counties received anywhere from a few hundredths of an inch of rain to one-half of an inch, with the greatest amounts in the Inland Empire and northern San Diego County valleys. The upper low moved across San Diego and Imperial Counties on the 21st, producing intense thunderstorms over the mountains and deserts, as well as a significant dust storm that moved up the Coachella Valley. The mountain locations of San Diego and Riverside Counties received up to one-half of an inch of rain, while the San Diego County deserts received up to 1.30 inches. One-inch hail was reported with thunderstorms in Nuevo and Mount Laguna/Pine Valley.

Hail in RIVERSIDE, CALIFORNIA
From 20-AUG-14 07:00:00 to 20-AUG-14 07:45:00 (PST-8)
Location: NUEVO
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A spotter reported hail up to one inch in Nuevo from a thunderstorm.

Flash Flood in SAN DIEGO, CALIFORNIA
From 21-AUG-14 12:00:00 to 21-AUG-14 13:00:00 (PST-8)
Location: (CZZ)CAMPO
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A spotter in Campo reported flash flooding and pea size hail at CA Highway 94 and Shookey road.

Flood in SAN DIEGO, CALIFORNIA
From 21-AUG-14 17:00:00 to 21-AUG-14 18:00:00 (PST-8)
Location: SAN JUAN HOT SPGS
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Amateur Radio

A ham radio spotter is reporting up to 6 inches of water on the road in the 35000 block of Highway 79 near Warner Springs.

Dust Storm in COACHELLA VALLEY, CALIFORNIA
From 21-AUG-14 15:00:00 to 21-AUG-14 16:00:00 (PST-8)
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A spotter reports a dust storm producing quarter mile visibility in Cathedral City, with winds estimated at 15-20 mph. A haboob in Palm Springs felled a tree onto a pickup truck containing a man who was injured and taken to the hospital. Peak wind speeds at the nearby Palm Springs ASOS were 40 mph at that time. The dust storm then proceeded down the Coachella Valley, reaching the Thermal Airport, whose ASOS reported one-quarter mile visibility in dust and 40 knot wind gusts.

Hail in RIVERSIDE, CALIFORNIA
From 20-AUG-14 04:00:00 to 20-AUG-14 04:30:00 (PST-8)
Location: MENIFEE
Magnitude: 1.00 
Property damage: 0.50K
Crop damage: 0.00K
Reported by: Public

The public reported 1-inch hail in Menifee from an early morning thunderstorm. Local news media reported large hail cracked a vehicle windshield in Menifee from the same storm.

Lightning in RIVERSIDE, CALIFORNIA
From 20-AUG-14 15:00:00 to 20-AUG-14 15:45:00 (PST-8)
Location: RIVERSIDE
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A spotter reported lightning struck and ignited fires in two palm trees near the community college. The fires were put out. Lightning also struck the technology building on campus, knocking out power.

Hail in SAN DIEGO, CALIFORNIA
From 21-AUG-14 11:30:00 to 21-AUG-14 12:00:00 (PST-8)
Location: MT LAGUNA AFS
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

One inch plus hail reported by the observers at the Mt. Laguna Observatory.