Thunderstorms produced large hail and damaging winds at numerous locations in northwest Iowa during the evening of May 1st. There was also one report of a tornado.

Hail in SIOUX, IOWA
From 01-MAY-12 18:22:00 to 01-MAY-12 18:22:00 (CST-6)
Location: FAIRVIEW
Magnitude: 1.50 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in LYON, IOWA
From 01-MAY-12 18:34:00 to 01-MAY-12 18:34:00 (CST-6)
Location: INWOOD
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Large hail was accompanied by wind gusts estimated up to 55 mph.

Hail in LYON, IOWA
From 01-MAY-12 18:45:00 to 01-MAY-12 18:45:00 (CST-6)
Location: ALVORD
Magnitude: 2.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Large hail was accompanied by strong winds. Leaves were stripped from numerous trees.

Hail in LYON, IOWA
From 01-MAY-12 19:15:00 to 01-MAY-12 19:15:00 (CST-6)
Location: LAKEWOOD
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Thunderstorm Wind in O'BRIEN, IOWA
From 01-MAY-12 20:15:00 to 01-MAY-12 20:15:00 (CST-6)
Location: SHELDON
Magnitude: 64.00 MG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: ASOS

Thunderstorm winds blew down trees and power lines.

Thunderstorm Wind in O'BRIEN, IOWA
From 01-MAY-12 20:17:00 to 01-MAY-12 20:17:00 (CST-6)
Location: SANBORN
Magnitude: 70.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm winds damaged several outbuildings on three farmsteads.

Thunderstorm Wind in O'BRIEN, IOWA
From 01-MAY-12 20:20:00 to 01-MAY-12 20:20:00 (CST-6)
Location: SANBORN
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm winds caused tree damage, including numerous branches up to 3 inches in diameter blown down.

Thunderstorm Wind in OSCEOLA, IOWA
From 01-MAY-12 20:35:00 to 01-MAY-12 20:35:00 (CST-6)
Location: OCHEYEDAN
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm winds caused tree damage, including several branches blown down.

Tornado in CLAY, IOWA
From 01-MAY-12 20:40:00 to 01-MAY-12 20:45:00 (CST-6)
Location: MONETA
Tornado F-scale: EF0
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A tornado damaged several power poles.

Thunderstorm Wind in O'BRIEN, IOWA
From 01-MAY-12 20:44:00 to 01-MAY-12 20:44:00 (CST-6)
Location: SUTHERLAND
Magnitude: 65.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm winds caused tree damage.

Thunderstorm Wind in CLAY, IOWA
From 01-MAY-12 20:55:00 to 01-MAY-12 20:55:00 (CST-6)
Location: SPENCER
Magnitude: 56.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm winds caused tree damage, including numerous trees blown down. The winds also  blew out windows.

Thunderstorm Wind in CLAY, IOWA
From 01-MAY-12 20:56:00 to 01-MAY-12 20:56:00 (CST-6)
Location: ROYAL
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm winds caused tree damage, including branches blown down.

Heavy Rain in LYON, IOWA
From 01-MAY-12 21:00:00 to 01-MAY-12 21:00:00 (CST-6)
Location: LITTLE ROCK
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Rainfall was measured at 2.92 inches.

Thunderstorm Wind in CLAY, IOWA
From 01-MAY-12 21:06:00 to 01-MAY-12 21:06:00 (CST-6)
Location: SPENCER
Magnitude: 62.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

A 71 mph gust was measured by RWIS equipment.

Thunderstorm Wind in CLAY, IOWA
From 01-MAY-12 21:18:00 to 01-MAY-12 21:18:00 (CST-6)
Location: DICKENS
Magnitude: 56.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm winds caused tree damage, and also damaged a roof.

Thunderstorm Wind in SIOUX, IOWA
From 01-MAY-12 20:00:00 to 01-MAY-12 20:00:00 (CST-6)
Location: ALTON
Magnitude: 76.00 MG
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Department of Highways

Thunderstorm winds damaged trees and power lines, and blew down a grain bin and cattle shed. The peak gust was measured by Iowa RWIS equipment.