Well, the National Weather Service and there thawed modelling didn't have anything to do with the problem at all... And they are responsible for the National Weather Service's work.
It was difficult for the cities to prepare for such an enormous flood. The National Weather Service (NWS) had forecast that the river would crest at 49 feet (14.9 m),[4] which was its highest level during the 1979 flood.[5] The cities had built dikes to this level, but the river continued to rise past it. Taken by surprise, the NWS did not upgrade its forecast until April 16, the day the river reached 49 feet.