Hot, sticky air hovers over the East Coast. Cool air is parked in the West. When they repeatedly collide, it storms over an already saturated Iowa.
This has been the stuck weather pattern for weeks, and it has led to tornadoes, thunderstorms, heavy rain, and now, record flooding.
Add to that La Niña in the Pacific Ocean, which some meteorologists think could be a factor.
La Niña—which is the cooler side of the El Niño weather phenomenon—causes weather changes around the world, including more rain and snow in some of the Midwest.
Even though La Niña itself is falling apart, its effects may still be felt in Iowa and Wisconsin.
(Read about El Niño and La Niña in Geographic Magazine.)
Already Saturated Ground
Iowa's rivers and land probably could have handled the massive rain—more than 15 inches (38 centimeters) in the last two weeks in some places—if it weren't for the heavy snow in the winter and lots of rain in the early spring, said Rob Middlemis-Brown, director of the U.S. Geological Survey Water Center in Iowa City.
"The ground never dried out," he said.
That ground was saturated and rivers were already high when the latest batch of concentrated localized storms started in late May, leaving water nowhere to go but over riverbanks.
Great Flood of '93
For parts of Iowa and southern Wisconsin, this year's flooding is worse than the 1993 great Mississippi and Missouri river floods, said Ken Kunkel, interim director of the Illinois Water Survey.
More rain is falling and in a shorter time now than in 1993. But for the entire Midwest as a whole, it was worse 15 years ago, he said.
But give this year more time, he added. The 1993 flooding peaked in July and August. Flooding for the broader region this year could be as bad as 1993 or worse if current patterns hold, Kunkel said.