Missouri River flood hits unprecedented flow rates

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 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.

Flooding along the Missouri River has already broken two levees and closed two portions of I-29, a key trucking route that extends from Kansas City through Iowa, South Dakota and North Dakota to the Canadian border. A 20-mile stretch between Council Bluffs and the Missouri Valley area is closed, as well as a 22-mile section in southwest Iowa and northwest Missouri, causing significant disruptions to the trucking industry.


Figure 1. Satellite image taken at 5:45pm CDT May 22, 2011, when the Joplin, Missouri tornado was occurring. The counter-clockwise flow of air around the spiraling low pressure system that caused the Joplin tornado drew large quantities of Gulf of Mexico air into Montana, creating record-breaking rains. Image credit: NASA/GSFC.



Figure 2. Levee breach along the Missouri River levee L-575 near Hamburg, Iowa, on June 14, 2011. The town of Hamburg is being protected by a new temporary levee. So far, only farmland has flooded. Image credit: U.S. Army Corps of Engineers.

Army Corps cranks up water releases on Missouri River dams to double the previous record
Six flood control dams lie on the Missouri River between eastern Montana and Sioux City, Iowa; these dams were built between 1940 and 1964. As water from this spring's record precipitation have flowed into the Missouri River basin, the reservoirs behind these dams have risen to record levels. On May 31, the Army Corps of Engineers was forced to open the the spillway gates on the massive Garrison Dam, 50 miles northwest of Bismark, North Dakota. It was the first time since the dam was built in 1955 that the spillway gates were opened. (Remarkably, during 2007 and early 2008, Lake Sakakawea water levels behind Garrison Dam were the lowest since the dam was built--46 feet below the current level--thanks to a decade-long drought.) On June 3, as the record flood progressed downstream, the spillway gates on the Big Bend Dam opened for the first time since that dam was completed in 1964. This week, the Army Corps of Engineers increased water flowing through all six dams to more than double the previous highs set during the floods of 1975 and 1997. The flow rates are now a massive 150,000 cubic feet per second, 1.5 times greater than the typical flow of Niagara Falls. These extreme flow rates will need to be maintained into at least mid-August, and are expected to severely strain levees on the Missouri River as it flows through North Dakota, South Dakota, Nebraska, Iowa, Missouri, and Kansas. According to a press conference put on by NWS and the Army Corps last week, the Missouri River flood control system is based on an 1881 estimate of the maximum amount of water an extreme flood season could generate--40 million acre-feet of water during the spring and summer flood season. However, this year's flood is expected to pump 42 - 43 million acre feet of water into the system, stressing it beyond its designed limits. In May alone, the Missouri River basin just upstream from Sioux City, Iowa, received 10.2 million acre feet of water, more than 25% above the previous May record of 7.2 million acre feet set in 1995. Additional levee failures along the Missouri are likely this summer, particularly if widespread heavy summer rains occur.


Figure 3. The Oahe Reservoir Stilling Basin north of Pierre, S.D., on June 5, 2011. The U.S. Army Corps of Engineers increased the water releases from the Oahe Dam into the stilling basin to a record 147,000 cubic feet per second (cfs) of water release on June 8. The previous record was 59,000 cfs in 1997. Image credit: U.S. Army Corps of Engineers/ Carlos J. Lazo

Four-day period of critical fire conditions expected in the Southwest
Powerful southwest winds of 20 - 30 mph, gusting to 40 mph will continue through Saturday in Eastern Arizona and western New Mexico, making progress containing the region's severe fires difficult. Even worse conditions are begin predicted for Sunday, when NOAA's Storm Prediction Center forecasts forecasts that wind gusts up to 50 mph will occur. With hot conditions and humidity values below 10%, these are likely to be among the worst fire conditions the region has seen this year.

While the exceptional drought gripping Arizona is largely to blame for terrible fire conditions this year, unusually windy and dry weather has also been a significant factor. These windy and dry conditions have been caused, in part, by a stronger-than-average jet stream over the region. According to the National Weather Service in Phoenix, the period April-May 2011 was the 11th windiest and had the 6th lowest average relative humidity value on record in Phoenix. Combined, it was the 3rd windiest-driest April-May on record.

Our weather historian, Christopher C. Burt, has an interesting post on The Worst Wild Fires in World History. Arizona's Wallow Fire, at 750 square miles, has a long way to go before matching the largest fire in U.S. history, the great Peshtigo Fire of 1871. That fire burned 5,938 square miles of Wisconsin and Michigan.

Tallahassee hits 105°, their hottest day on record
On Wednesday June 15 at 307 PM EDT, the Tallahassee Regional Airport in Florida recorded a high temperature of 105 degrees. This temperature breaks the previous all time high temperature record for Tallahassee of 104 degrees, set most recently on June 20th 1933. The period of record for Tallahassee dates back to 1892.

The Atlantic is quiet
The Atlantic is quiet, with no tropical cyclones predicted over the next seven days by the reliable computer models. However, the GFS model predicts that moisture will begin increasing early next week in the western Gulf of Mexico, and a tropical disturbance could form next week in the Gulf, bringing much-needed rains to the coast of Texas. Droughts of the magnitude of the current Texas drought are hard to break, though, so I'd like to see more support from the models before believing in this forecast.

Have a great weekend everyone! I'll be back Monday with a new post.

Jeff Masters