At least five people are dead after a powerful storm system of more than 20 tornadoes swept through the central United States on Wednesday with high winds that spread wildfires and knocked down power lines, leaving hundreds of thousands of customers without electricity. Most of the fatalities occurred in vehicle crashes. One person driving a truck in Iowa died when the vehicle was hit by a strong gust of wind, rolling it over and into a ditch, according to a state patrol crash report. Three people in Kansas died in car crashes, while a man in Minnesota died when a 40-foot tree fell on him, according to officials. Unprecedented Midwest wind storm caps 2021's siege of extreme weather The National Weather Service confirmed that at least 21 tornadoes touched down in Iowa, Minnesota, Nebraska and Wisconsin. At least 13 of those touched down in Iowa, officials said Thursday. The unusual weather appeared to be fueled by record-breaking warm temperatures coupled with a jet stream that meteorologist Jeff Masters said took on a "very unusually contorted pattern." It also came just days after devastating tornadoes in nine states left dozens dead. The National Weather Service reported a tornado near Rochester in southeastern Minnesota, the state's first on record in December. Several tornadoes reported in western and central Iowa also were December firsts for those parts of the state. And a record was set Wednesday for the most hurricane-force winds of 75 mph or higher in a single day since 2004, according to the Weather Service. In all, more than 36 million people in an area between New Mexico and Michigan were under high-wind warnings, as gusts of up to 100 mph sent roofs flying and toppled tractor-trailers on highways from Colorado to Iowa. "I've been a meteorologist for 40 years, and I've seen things that have floored me and boggled my mind," said Masters, an extreme-weather expert at Yale Climate Connections and a founder of Weather Underground. "But I would have never thought I would see extremity of the weather I saw last night. The winds were unbelievable." More than 340,000 customers were without power in Wisconsin and Michigan as of Thursday afternoon, according to PowerOutage.us, which tracks outages.