Lack of winter snowfall lowers spring flood risk

Omaha — The National Weather Service on Feb. 16 reported that there is little chance of major spring flooding in Iowa this spring, citing a range of factors including below normal snowfall this winter and generally dry soil conditions that extended through late fall and early winter. From Iowa upstream in the Missouri River basin, the weather service reported below average mountain snowpack and very little snow in the Northern Plains. The risk of widespread spring flooding due to snowmelt is classified as below normal in western North Dakota as well, with the weather service reporting that drought conditions have expanded this winter across much of the state. About the only risk of flooding along the Missouri and James rivers in the Dakotas would be through heavy spring rains or ice jams, the report said. Figures for the Red River in eastern North Dakota show the chances for minor flooding along the river at less than 33 percent in most areas. Fargo, N.D., has a 53 percent chance of minor flooding and a 6 percent chance of major flooding this spring. The lack of winter snowfall in the upper Missouri River Basin has provided some flexibility for the U.S. Army Corps of Engineers, who have begun releasing more water from the Missouri’s reservoir system to prepare for spring runoff. The move will create an additional 500,000 acre-feet of flood control storage for the 2012 runofff season on the Missouri River Mainstem Reservoir System, the Corps reported. If February weather conditions allow it, the Corps says it will evacuate an additional 100,000 acre-feet of water in the coming weeks. The Corps said warmer-than-normal temperatures throughout the basin in the first half of January prevented ice formation on rivers, resulting in above-average runoff during January that totaled 980,000 acre-feet above Sioux City, Iowa, which is about 131 percent of normal. When colder temperatures hit later in January, those rivers froze over and inflows to the reservoir system were reduced. The Missouri River Basin runoff for the 2012 calendar year is forecast to total 25.6 MAF, just slightly above the historical norm of 24.8 MAF, the Corps said. By contrast, runoff for the 2011 calendar year totaled 61.2 MAF, 247 percent of normal and the highest amount in the Corps’ 114 years of record keeping for the basin.