Jeff Masters’s blog on Weather Underground offers some interesting details on Missouri River flooding and related topics. Here’s a clip; there’s much more here:
The most expensive tornado/severe weather disaster in American history is the great May 21 – 26, 2011 storm that spawned the Joplin, Missouri EF-5 tornado. According to catastrophe modeling firm AIR Worldwide, insured damages from that storm will amount to $4 – $7 billion, the greatest damages ever for a spring severe weather outbreak.
However, the damages from the huge, slow-moving low pressure system that spawned the Joplin tornado have not yet been fully realized. The powerful storm pumped huge quantities of warm, moisture-laden air from the Gulf of Mexico northwestwards into Montana, where the moisture condensed into record-breaking heavy rain and snow. In portions of eastern Montana, the storm brought a year’s worth of precipitation in a week, swelling the tributaries of the Missouri River to unprecedented heights. Billings, Montana recorded 9.54″ of precipitation in May, its single wettest month on record, and not far from its annual average precipitation of 14.5″.
A great 100-year flood has arrived along the Missouri River and its tributaries from Montana to Nebraska. Record spring rains, combined with snow melt from record or near-record winter and spring snows, brought the Missouri River at Williston, North Dakota to 30′ today (June 17), two feet above the record crest set in 1912.
Tributaries to the Missouri, such as the Souris River in North Dakota and the North Platte River in Nebraska, are also flooding at all-time record heights. With warm summer temperatures and 2 – 5″ of rainfall expected over much of the area during the coming week, snow melt and rain runoff will swell area rivers even further, creating an even more dangerous flood.