ABERDEEN, S.D. – A rare and particularly dangerous storm system known as a derecho moved through the Northern Plains during the late afternoon and early evening hours of Thursday, May 12th, including eastern South Dakota and west central Minnesota.
Derechos feature unusually widespread wind damage, and this was one of the most extreme examples on record. It raced north-northeastward at 50 to 70+ mph, and produced measured straight-line winds of between at 60 to over 100 mph. This is about the same as a category 1 hurricane (74 to 95 mph) and an EF0 to EF1 tornado (65 to 110 mph) over a large area.
Significant blowing dust was also reported, especially across southeastern South Dakota. Additionally, several tornadoes were reported and confirmed. Some of the worst damage occurred in Hamlin and Deuel counties.
An EF2 tornado, with wind speeds up to 120 mph passed through the town of Castlewood, SD. Many significantly damaged or destroyed structures resulted. Another farmstead south of Gary, SD was also devastated by a tornado. At this location wind speeds are estimated at 135 mph, which ranks it as a high end EF2 tornado.
The National Weather Service in Aberdeen deployed three damage survey crews to document and rate tornado damage. Seven tornados were recorded.
