Record Spring Rain and Snow Pose Major Flood Risks for the West and Missouri River

Record Spring Rain and Snow Pose Major Flood Risks in the West and along the Missouri River

With the Mississippi River now slowly receding from its record crest at the end of May a new major flood risk is developing along the Missouri River from Montana to Nebraska and snowmelt is likely to create significant flooding in many river valleys and lakes throughout the Rocky Mountain region.

Missouri River Flooding

National Weather Service Hydrologist Mark Fuchs warned on Thursday (June 2nd) that “nearly every reservoir in the Missouri River Basin has been completely used up, with releases from five to six dams on the upper Missouri exceeding 100,000 cubic feet per second (cfs), higher than any of them have ever experienced.” Historic flooding along the length of the river from Montana to Nebraska is likely to rival the record crests observed during the great flood of 1993.



The heaviest observed monthly rainfall on record during May in portions of Montana, combined with the melting of near-record snow packs, is the culprit leading to this situation. Billings, Montana recorded 9.54” in May, obliterating its former single-wettest month on record of 7.71” set in May of 1981 (the average annual precipitation for Billings is just 14.5”!). An all-time 24-hour rainfall of 3.35” was observed on May 24-25 in the city (old record was 3.19” on April 27-28, 1978). Almost every site in eastern Montana, eastern Wyoming, and western South Dakota recorded their wettest May on record. Portions of western North Dakota and eastern Montana have also endured their snowiest winter season on record (including Williston, North Dakota with 107.2” and Glasgow, Montana with 108.6”) and the melting of this has filled local reservoirs to the brim.

Tributaries to the Missouri, such as the Souris River in North Dakota and the North Platte River in Nebraska, are already flooding at all-time record heights.



Any additional rainfall across the region and snow melt from the Montana Rockies will likely cause a record crest to develop on the upper Missouri River that will work its way downstream to the Mississippi at St. Louis sometime later this month. Cities that are likely to be affected by flooding of record proportions include Williston and Bismarck, North Dakota; Pierre, the state capital of South Dakota, Sioux City, Iowa, and even perhaps Kansas City, Missouri.



The Missouri River has already begun to overflow its banks at Sioux City, Iowa as the photo taken on May 31st indicates. Photo from Associated Press.

Below are the flood stage predictions for the Missouri River from Sioux City to St. Charles (where the Missouri River reaches the Mississippi):




The worst flood in modern history of the Missouri River was that of 1993, ironically the same as the last time (previous to this year) that the Mississippi recorded its greatest flood on record. I say ironically because in 1993 the two rivers flooded for the same reason (heavy spring rains) and at the same time, yet this year the two rivers are flooding at different times for slightly different reasons; still because of record spring rains but this time with upstream snow melt more in the equation.

Rocky Mountain Region Flooding Potential

The extraordinary snowfall season of 2010-2011 continues into June for the Central and Northern Rocky Mountain and Intermountain Regions. Ely, Nevada just received an additional 9.0” of snow on May 28-29 breaking the town’s all-time snowiest season on record with a total of 110.4” (amazingly the previous record was just last season with 107.0”—-records go back to 1890). In Colorado the snow depths at the 10,000' snotel locations are still running as high as 169” (14 feet deep!) at Tower site. Even at the relatively low site of Dry Lake at 8,400” the snow is still an impressive 41” deep as of June 2. In Wyoming snow depths are still over 120” (10 feet)at most 10,000-foot snotel sites, and in Utah Snowbird still has 135” on the ground at the 9,640-foot level. The deepest snow in the nation, however, is in California’s Sierra where 181” (15 feet) remains on the ground at Leavitt Lake, 9,400’. Donner Summit has so far recorded over 800” of snow this season with more expected this weekend. Its all-time seasonal snowfall record of 819” (set in 1937-1938) is in jeopardy.

All of this is probably going to melt very quickly this month and send torrents water into the valley streams, rivers, and lakes. Furthermore, low elevation sites such as Salt Lake City have experienced their wettest spring on record: Salt Lake City has just completed its wettest three month (March-May) period on record with 11.73” of precipitation (previous record was 10.39” during March-May 1876). It is very likely that Salt Lake City will see some serious urban flooding later this month. The last big snowmelt flood in the city occurred in May 1983.



Downtown Salt Lake City’s streets turned into rivers in late May and early June 1983 following a rapid warm up that melted deep snow in the Wasatch Mountains. Here pedestrians cross a makeshift bridge at the intersection of State Street and 100 South Street. The Federal Building is in the background. Photo from National Weather Service archives.

The Great Salt Lake is no longer in danger of flooding since pumps were installed on the west side of the lake in 1987 to pump water into the desert.

To keep track of the coming floods in the West and along the Missouri River follow wunderground.com's severe weather alerts page for the latest information.