A weather expert at Iowa State University says a trough in the jet stream that’s parked over the Rocky Mountains is at the root of the severe storms that have struck Iowa.
ISU meteorology professor Bill Gallus says there’s been a "surprisingly consistent" weather pattern over Iowa for the past few weeks. "We just have this big trough in the Rockies or off to the west of Iowa that has been pretty much been sitting there for the last two or three weeks and that causes us to have fairly strong winds out of the southwest up high in the atmosphere which is a good scenario for helping to pull lots of moisture up from the Gulf and places to our south and to give us the large amounts of wind in the atmosphere to help create very strong thunderstorms that produce severe weather and can lead to flooding rains," Gallus says.
Gallus uses the term "training" to describe how the storms are quickly moving across Iowa, but still dumping huge amounts of rain in one area. "We have storms keep forming in the same spot and then taking the same track over and over so it’s really what we call ‘training’ in meteorology because it looks a lot like the cars on a train on a railroad," Gallus says.
Gallus cites the Mason City area as an example, as thunderstorm after thunderstorm rolled through on Saturday night, every 30 or 40 minutes. "The individual storms are moving along quickly which is what you would expect with the very strong winds up so high, but the weather pattern has been so good at creating thunderstorms that you just keep forming new ones in the same spot and then each new one travels down the same track and hits the same places over and over," Gallus says.
Gallus predicts the weather pattern will change slightly by Friday or Saturday, but unfortunately there’ll be more thunderstorms before that shift occurs at week’s end.
Bill Gutowski, another meteorology professor at ISU, says the weather fluctuates on its own all the time. "As a consequence, it’s not surprising that you get these periods when there is lots of rain falling and things are very wet," Gutowski says. "Obviously people are remembering 1993. You know, that was 15 years ago so it’s not like it’s been happening every single year or something like that so it’s not unexpected, it’s just that we can’t necessarily predict exactly when it will be occurring."
The floods of 1993 were often characterized as a "100-year flood" but Gutowski says there’s a bit of "fuzziness" in that term. "It’s important to keep in mind that when terms like ‘100-year flood’ are used it doesn’t mean that only once every 100 years it’s going to happen. It’s a statistical probability," Gutowski says, "and so it’s not impossible to have two ‘100-year’ type floods occur 15 years apart, if that’s what’s happening."