MITCHELL, S.D. (MITCHELLNOW) The National Weather Service has confirmed that multiple tornadoes touched down during last Monday’s storms. One EF-1 tornado northwest of Dixon damaged buildings and power poles, while an EF-2 near Bonesteel tore through a home, outbuildings, and utility lines. Another EF-1 hit Alvord, Iowa, damaging a barn and trees. Officials said fire crews in Gregory County were chasing storms and fighting fires at the same time. The system later became a derecho, with wind gusts reaching up to 90 miles an hour across southeast South Dakota and northwest Iowa, leaving widespread damage…