Melting snow from the Rocky Mountains combined with heavy spring rains have swelled the Missouri River to dangerously high levels, prompting North and South Dakota residents to prepare for flooding. The Army Corps of Engineers has already opened floodgates at six dams and has been releasing reservoir water into the river in an attempt to make room for new snowmelt, but it seems to be insufficient. More rain is expected later this week. "It's the perfect storm, but in the worst sense," said a meteorologist with the National Weather Service in Aberdeen, South Dakota. As many as 12,000 people have been forced to evacuate the North Dakota city of Minot, and another 1,000 homes in Bismarck are under voluntary evacuations.