On the evening of May 4, 2007, at around 7:30 p.m., a young forecast meteorologist named Mike Um­scheid began tracking a storm in northern Oklahoma. He watched as it grew, in a mere 15 minutes, from “this little blip” on a radar monitor to a supercell—more colloquially known as a violent thunderstorm. “It was amazing how quickly it developed,” he recalls. This was the height of tornado season, and Umscheid, with three other meteorologists at the National Weather Service in Dodge City, Kansas, was entrusted with the safety of 27 counties in the state’s southwest.

The storm he was tracking was unusually intense; it retained its potency for six and a half hours, cyclically producing an estimated 22 tornadoes

At 9:19 p.m., using what he calls a “nifty little tool”—a forecast and warning software program—he sketched a polygon to plot the trajectory of one increasingly violent tornado. “Oh, my God,” he thought, “it’s making that northward turn.”