- Associated Press - Friday, August 28, 2015

SIOUX FALLS, S.D. (AP) - A National Weather Service meteorologist says it wasn’t a big thunderstorm that caused flash flooding in Sioux Falls but a series of thunderstorms.

Todd Heitkamp says such weather systems are known as “train echoes,” because a series of storms moves over the same area, similar to a train of boxcars.

The weather service forecast 2-4 inches of rain Thursday evening, which Heitkamp says was an accurate average of what fell over the area. He says there’s no way to forecast the extreme heavy rainfall that fell in some areas, such as 2.75 inches measured in one gauge in less than half an hour.

Heitkamp says the last time there was a similar weather event in Sioux Falls was 11 years ago.



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