Severe thunderstorms developed between Custer and Hermosa; producing large hail, gusty winds, very heavy rain, and flash flooding.

Thunderstorm Wind in CUSTER, SOUTH DAKOTA
From 17-AUG-07 17:21:00 to 17-AUG-07 17:21:00 (MST-7)
Location: HERMOSA
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in CUSTER, SOUTH DAKOTA
From 17-AUG-07 17:40:00 to 17-AUG-07 17:40:00 (MST-7)
Location: CUSTER
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in CUSTER, SOUTH DAKOTA
From 17-AUG-07 17:45:00 to 17-AUG-07 17:45:00 (MST-7)
Location: HERMOSA
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Hail in PENNINGTON, SOUTH DAKOTA
From 17-AUG-07 18:00:00 to 17-AUG-07 18:00:00 (MST-7)
Location: RAPID CITY
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Thunderstorm Wind in PENNINGTON, SOUTH DAKOTA
From 17-AUG-07 18:00:00 to 17-AUG-07 18:00:00 (MST-7)
Location: RAPID CITY
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Thunderstorm Wind in CUSTER, SOUTH DAKOTA
From 17-AUG-07 18:05:00 to 17-AUG-07 18:05:00 (MST-7)
Location: HERMOSA
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Employee

Thunderstorm Wind in CUSTER, SOUTH DAKOTA
From 17-AUG-07 18:40:00 to 17-AUG-07 18:40:00 (MST-7)
Location: FAIRBURN
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Flash Flood in CUSTER, SOUTH DAKOTA
From 17-AUG-07 18:00:00 to 17-AUG-07 20:00:00 (MST-7)
Location: CUSTER
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Nearly stationary thunderstorms dropped two to four inches of rain in less than two hours in the Custer area. Flooding was reported throughout much of the City of Custer, with many streets from downtown to areas south and east of town covered by water. No significant damage was reported.

Flash Flood in CUSTER, SOUTH DAKOTA
From 17-AUG-07 18:00:00 to 18-AUG-07 03:00:00 (MST-7)
Location: HERMOSA
Flood cause: Heavy Rain
Property damage: 3.00M
Crop damage: 0.00K
Reported by: NWS Storm Survey

Heavy rain estimated at four to six inches fell west of Hermosa between 6 pm and 8 pm MST. Battle and Grace Coolidge Creeks overflowed their banks and several dry canyons filled with water and drained into the creeks. State highways 40 and 36 were flooded in numerous spots. A river gauge on Battle Creek just east of Hermosa crested at 14.91 feet at 9 pm, rising from 2.63 ft at 7:30 pm and above the flood stage of 8.0 feet. About six inches of water covered Highway 79 at the Battle Creek bridge. A railroad bridge about 3/4 mile downstream became clogged with debris and water rose behind the embankment and flooded six homes. At about 8:30 pm MST, a section of the embankment failed, flooding a new subdivision on the other side. All of the approximately 20 houses were damaged; three homes were washed off their foundations, and one of those houses was carried a half a mile east of the subdivision by the flowing water. There were no injuries.

Thunderstorm Wind in CUSTER, SOUTH DAKOTA
From 17-AUG-07 18:05:00 to 17-AUG-07 18:05:00 (MST-7)
Location: HERMOSA
Magnitude: 56.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Employee