ASHBY, Minn. — A report from the National Weather Service rates the Wednesday, July 8, tornado in Otter Tail County as an EF4 with peak wind speeds of 170 mph.

The report says the tornado was produced by a supercell thunderstorm at 5:08 p.m. It started as a weak tornado with a rating of EF0-EF1 with 65-110 mph winds in northern Grant County, Minn., but escalated as it moved into southern Otter Tail County, becoming an EF2-EF3 rated tornado.

Starting point:

The tornado reached maximum EF3 intensity after it crossed over Highway 82 and destroyed a machine shop in Dalton, Minn., killing 30-year-old Seth Nelson, the weather service said.

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The report says the tornado then continued northeast and transitioned to the intensity of an EF4. It destroyed a rural homestead along 120th Street and continued northeast destroying trees and crops until the funnel dissipated at 5:39 p.m. near 325th Avenue in Dalton.

Ending point:

The EF (Enhanced Fujita) rating scale categorizes tornadoes by wind speed and destruction:

  • EF0: 65 to 85 mph
  • EF1: 86 to 110 mph
  • EF2: 111 to 135 mph
  • EF3: 136 to 165 mph
  • EF4: 166 to 200 mph
  • EF5: Over 200 mph