Two long-track supercell thunderstorms caused widespread damage across western South Dakota on Aug. 11, producing hail as large as 4 inches in diameter and wind gusts reaching 111 mph, according to the National Weather Service in Rapid City.
One storm developed in the northern Black Hills before moving southeast through the Nemo, Johnson Siding, Rockerville, Hayward and Hermosa areas. Hail up to 3.6 inches in diameter was reported near Hermosa, while hail up to 4 inches was reported in the Oglala and Pine Ridge areas.
The storm caused widespread damage, including shattered windows, damaged roofs, dented vehicles and destroyed carports. In Oglala, damage to 26 school district vehicles, including all 10 school buses, forced a delay to the start of the school year.
A second supercell moved into South Dakota from southeastern Montana and produced damaging hail and extreme winds. A 111-mph wind gust was reported 13 miles northeast of Newell.
The storm later produced wind gusts of 102 mph near Cactus Flat, 96 mph south of White River and 90 mph near Rosebud. Several semitrailers and other vehicles were blown over along Interstate 90.
The storm caused significant structural and tree damage across parts of Mellette, Todd and Tripp counties. The Rosebud fairgrounds cook shack collapsed, while the Tokala Inajinyo Youth Leadership Mentoring Program Resource Center was destroyed.
At least 53 homes on the Rosebud Reservation were reported uninhabitable because of the severe wind damage. One person was seriously injured after an RV was blown over and rolled about 50 feet near Rosebud.
The National Weather Service also reported 78 power poles were damaged or knocked down across Mellette County.