An isolated supercell developed across south central South Dakota late evening along an advancing cold frontal boundary. With appreciable DCAPE and deep-layer effective shear, upscale growth occurred rapidly with the development of widespread damaging winds, which spread out of eastern South Dakota into northwest Iowa.

Thunderstorm Wind in SIOUX, IOWA
From 17-SEP-21 00:07:00 to 17-SEP-21 00:09:00 (CST-6)
Location: MAURICE
Magnitude: 55.00 MG
Reported by: AWOS

Automated weather station KSXK measured thunderstorm wind gusts.

Thunderstorm Wind in SIOUX, IOWA
From 17-SEP-21 00:34:00 to 17-SEP-21 00:36:00 (CST-6)
Location: BOYDEN
Magnitude: 61.00 EG
Reported by: Law Enforcement

Large tree branches were downed by thunderstorm wind gusts.

Thunderstorm Wind in O'BRIEN, IOWA
From 17-SEP-21 00:29:00 to 17-SEP-21 00:31:00 (CST-6)
Location: SHELDON MUNI ARPT
Magnitude: 70.00 EG
Property damage: 350.00K
Reported by: Emergency Manager

A roof was completely torn off the end of a strip mall and deposited in pieces on the roadway. Property damage costs are a rough estimate.

Thunderstorm Wind in O'BRIEN, IOWA
From 17-SEP-21 00:45:00 to 17-SEP-21 00:47:00 (CST-6)
Location: SANBORN
Magnitude: 61.00 EG
Crop damage: 20.00K
Reported by: Law Enforcement

Large tree limbs were downed by thunderstorm wind gusts. Crop damage is an estimate from insured losses. Information provided by the United States Department of Agriculture.

Thunderstorm Wind in SIOUX, IOWA
From 17-SEP-21 00:33:00 to 17-SEP-21 00:35:00 (CST-6)
Location: HULL
Magnitude: 70.00 EG
Property damage: 25.00K
Reported by: Law Enforcement

A large construction shed was lifted and thrown into a nearby corn field. Property damage costs are a rough estimate.

Thunderstorm Wind in SIOUX, IOWA
From 17-SEP-21 00:34:00 to 17-SEP-21 00:36:00 (CST-6)
Location: BOYDEN
Magnitude: 61.00 EG
Property damage: 50.00K
Reported by: Emergency Manager

The doors of a school bus garage building were blown in by thunderstorm winds, which resulted in failure of the most of the roof and an exterior wall. Property damage costs are a rough estimate.

Thunderstorm Wind in SIOUX, IOWA
From 17-SEP-21 00:15:00 to 17-SEP-21 00:17:00 (CST-6)
Location: ORANGE CITY
Magnitude: 52.00 EG
Reported by: Social Media

A large tree branch was downed by strong thunderstorm wind gusts.

Thunderstorm Wind in SIOUX, IOWA
From 17-SEP-21 00:33:00 to 17-SEP-21 00:35:00 (CST-6)
Location: BOYDEN
Magnitude: 61.00 EG
Property damage: 5.00K
Reported by: Law Enforcement

Several power lines were downed by thunderstorm wind gusts.

Thunderstorm Wind in SIOUX, IOWA
From 16-SEP-21 23:50:00 to 16-SEP-21 23:52:00 (CST-6)
Location: HAWARDEN MUNI ARPT
Magnitude: 55.00 MG
Reported by: Mesonet

Iowa RWIS station FW6302 in Hawarden measured thunderstorm wind gusts.

Thunderstorm Wind in O'BRIEN, IOWA
From 17-SEP-21 00:26:00 to 17-SEP-21 00:28:00 (CST-6)
Location: SHELDON MUNI ARPT
Magnitude: 56.00 MG
Reported by: AWOS

Automated weather station KSHL measured thunderstorm wind gusts.

Thunderstorm Wind in OSCEOLA, IOWA
From 17-SEP-21 00:28:00 to 17-SEP-21 00:30:00 (CST-6)
Location: ASHTON
Magnitude: 56.00 MG
Reported by: Mesonet

Iowa RWIS site near Ashton measured thunderstorm wind gusts.