April tornado in Keota. (photo by Josh Franzen via NWS)
State Climatologist Justin Glisan says Iowa has been in a severe weather drought for the past three years. So far this year, there have been three dozen confirmed tornadoes in the state.
“If you look at the climate trends, it looks like ‘Tornado alley’ is shifting further south,” Glisan says. “We have a more active storm track in what we call ‘Dixie Alley’ where you have wider scale tornado outbreaks.”
Over the past four decades, Iowa has been averaging 48 tornadoes a year. June has generally been the peak month for tornado activity in Iowa, but it appears there’s been just one tornado reported in the state this month. There were multiple tornadoes on March 31, though. The National Weather Service office in the Quad Cities confirmed at least 30 tornadoes in eastern Iowa and western Illinois that day.
“If you look at our records across the state and across the Midwest since 1950, we’re seeing less one off thunderstorm/tornado events. We’re seeing more outbreaks,” Glisan says. “…That has to do with a warmer atmostphere, more water vapor availability, more instability building in and so moving forward over the next several decades we can expect conditions for severe storms to increase, especially in that March, April, May time frame.”
Warm, humid air near the ground and cold, dry air above are the ingredients that spawn a tornado out of a thunderstorm. “We got into a situation in 2020 and 2021 in west central Iowa where you had thunderstorms forming and then just dissipating or moving around because there was no low level moisture to work with,” Glisan says, but he notes the latest research indicates relative humidity will be trending upward in the years ahead.
Glisan made his comments during a recent appearance on Iowa Press on Iowa PBS.