Historic flooding is a possibility on the Missouri river over the next several weeks and possibly months. The reason stems from extreme snow pack and rainfall in areas like Montana and the Dakotas running off into smaller rivers that feed into the larger Missouri River. There are dams along the Missouri River managed by the US Corps of Engineers to regulate the flow of the Missouri River, and the reservoirs have run out of storage of the excess runoff from the snow pack and heavy rainfall.
Towards the middle of June, the Army Corps of Engineers will release more than twice the record release of water from the Gavins Point Reservoir near Yankton, South Dakota. And it is likely the high release of water will continue through July and into August.
This rush of water will mean a very high base flow on the Missouri River, which means it won't take much rainfall to bring the Missouri River near St. Charles to historic levels.
For instance, assuming average rainfall across the Missouri River basin we would see a 28ft. to 37ft. crest on the Missouri in St. Charles. The record crest is 40.11ft. set in 1884. And again, that is assuming average rainfall.
Needless to say, we are going to have to watch the Missouri River for a very long time, and there could be several crests near record levels or even above, since this high water level will last for weeks to months.
Here is a link for more info.