DES MOINES, Iowa -- Much of Iowa, including Central Iowa, is a month behind a first tornado warning of the year.
"We are off to certainly the slowest start in the tornado warning polygon era, really in more than 25 years. It's very unusual since we're into the second week of May," says National Weather Service Meteorologist Rod Donovan.
Sine 2007, the National Weather Service has used the "tornado warning polygon" for severe weather warnings covering only the locations and people inside the polygon.
Donovan says the this year's later-arriving severe weather season is part of a decade-long trend.
"A lot of our (air) flow aloft is coming out of Canada and is not really conducive to severe thunderstorms or tornadic development. The Southern Plains has been much more active through the time period--warmer weather and frontal boundaries have been to our south" Donovan says.
He says Iowa severe weather seasons that have started later across the last decade have also ended later.
"Biggest increase in temperature has been in the fall, which kind of contributes to seeing that warmer weather and keeping the frontal boundaries around here--keeping our severe weather chances a least a little bit later than they were in the past," Donovan says.
He says there have been just two tornado warnings in Iowa this so far year--both on the same day in March in Southeast Iowa.
Images from the National Weather Service