EF 4 Tornado In Iowa In Early March "Very Unusual, Especially At That Magnitude"
The powerful EF4 tornado that caused devastation across Winterset and surrounding communities was "very unusual, especially that magnitude," Brad Small, a meteorologist at the National Weather Service in Des Moines, told Axios.
Most tornadoes occur in April and May in Iowa, but the warm and humid air over the weekend combined with the cold contributed to unstable conditions.
By the numbers: Saturday's violent storm broke a number of records from the last decade: the last EF4 tornado recorded in Iowa in March was from 1990. Last weekend's tornado was continuously on the ground for 69.5 miles the longest track in Iowa since 1984, when a tornado went for 117 miles.
It was the deadliest tornado since 2008, when a storm killed seven people in Parkersburg and two in New Hartford.
EDIT
https://www.axios.com/local/des-moines/2022/03/09/iowa-march-tornado-ef4-statistics