After severe weather earlier this month, some may have questions on how tornadoes are ranked.

National Weather Service Meteorologist Andrew Ansorge says that during the May 21st tornado outbreak, there was an EF4 tornado that struck Greenfield, along with an EF 3 in Adams County and an EF 2 tornado north of Des Moines. He mentions that these are still preliminary rankings that may change as surveys on the damage from each continues. Ansorge tells Raccoon Valley Radio how they differentiate which storms go on which level of the EF scale.

“So when we survey tornado damage, we look at different damage indicators. So that could be a tree, that could be a power pole, that could be a home or a business or sometimes a farm, outbuildings as well. And those all have been researched by structural engineers and meteorologists to get an idea of what kind of wind speed it would take to cause that kind of destruction. There’s varying degrees, so it could go from something like having shingles ripped off your house to, you know, completely destroyed homes, like what we saw in Greenfield. So we look at those things and try to make a determination on what kind of winds would cause that kind of damage.”

When considering the scale of the damage, Ansorge mentions that we don’t have to go back very far to find the last tornado that achieved an EF4 ranking in Iowa. He adds that that tornado struck between Sigourney and Washington on March 31, 2023, and that the last time the state saw an EF5 tornado was the Parkersburg Tornado in May of 2008.