A DNR climatologist called the geographic spread, number of tornadoes and number of deaths "a very unusual event." The dozens of funnel clouds could eclipse single-day record set in 1992.
It was a year's worth of tornadoes on one of Minnesota's most unusual nights of stormy weather.
The tornadoes that ripped through the state Thursday night, killing three people and injuring many more, exceeded the number that strike the state in an average year, according to data compiled by the Minnesota Climatology Working Group.
While officials caution that averaging tornado destruction from year to year is not a good way to spot trends, the storms are historic in quantity and scope.
Simply put, the state usually doesn't see that many funnel clouds hit such a broad geographic area in a single day, said Greg Spoden, a climatologist with the state Department of Natural Resources.
"In the modern era, the number of tornadoes, the geographic spread and, certainly, the number of fatalities... all mean that this was a very unusual event," Spoden said.
In Freeborn County in southern Minnesota, up to nine tornadoes tore up farms, injured dozens of people and killed a woman. In Wadena, in north-central Minnesota, 20 people were treated at the hospital for injuries.
Also in northwestern Minnesota, a man was killed in Polk County and a woman died in Otter Tail County.
Before Thursday, the most tornadoes confirmed in a single day in Minnesota was 27, on June 16, 1992. On average, Minnesota has fewer than 26 confirmed tornadoes a year.
Thursday's storms spawned dozens of funnel clouds, Spoden said, which are likely to eclipse the 1992 single-day tornado total. Thursday's powerful systems were fueled by strong southerly winds that brought very humid air into the state, National Weather Service meteorologist Matt Friedlein said. That air interacted with higher altitude winds from the west, driven by the jet stream. The high wind speeds from different directions and at different heights created rotational movement in the air.
The humidity also caused the formation of clouds with low bases that grew rapidly in size and height and were able to hold considerable moisture, including large hail, Friedlein said. The low cloud base made it possible for the rotational winds to form funnel clouds that could touch down and move across the land.
Since 1950, on average fewer than two people a year are killed by tornadoes in Minnesota. The last time more than one person was killed in a single day was on March 29, 1998, when two people were killed about 50 minutes apart in Comfrey and St. Peter. Three people were killed that year.
Before Thursday, the state's last tornado death was in 2008, when a funnel cloud tore through Hugo, killing a boy.
Staff writer Tom Meersman contributed to this report. James Walsh • 612-673-7428