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Unsettled Across Much of the U.S.

Heavy rain in the Mid-South could produce flash flooding. Rain will expand over the Lower and Central Mississippi Valley and across the Mid-Atlantic and Northeast through mid-week. Accumulating snow continues in the northern tier and 4-Corners. Pacific Northwest mountain and low elevation snow returns mid-week. Read More >

Overview

A 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 the most extreme example on record in terms of the number of measured significant wind gusts. 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 and visibility reductions were also reported, especially across southeastern South Dakota. Additionally, 34 tornadoes have been confirmed: 19 in Minnesota, 13 in South Dakota, and 1 in both North Dakota and Iowa. 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.

Widespread impacts resulted from this storm, including uprooted or snapped trees, significant property damage, power outages, tipped high-profile vehicles, as well as injuries and a couple fatalities across the region. On May 13th, South Dakota Governor Kristi Noem ordered a State of Emergency for storm response and ordered state personnel and resources to communities impacted by the damaging storms. A Presidential Disaster Declaration was later approved for South Dakota. The National Centers for Environmental Information, NCEI, determined this to be a billion-dollar disaster event

Image
Video of the Castlewood tornado, courtesy of Chris Schmidt.

 

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