Above-average rainfall and fast-melting snow led to above-average runoff in the upper Missouri River Basin in June. Runoff above Sioux City, Iowa, was 6.7 million acre-feet, 122 percent of average. The annual runoff forecast above Sioux City, Iowa is 29.2-million-acre feet, 114 percent of average, and about 2.4 million acre-feet higher than last month’s forecast.
Precipitation was normal to much-above-normal for June in much of Montana, southern and east-central North Dakota, and western South Dakota. Below-normal precipitation occurred in eastern South Dakota and into the lower Basin. Based on the July 1 System storage, flow support for navigation increased from minimum service to 1,500 cfs below full-service level. Per the guidelines in the Master Manual, this will also result in a full navigation flow support season ending December 1 at the mouth of the Missouri River.
Gavins Point releases were increased to 29,000 cubic feet per second in early July to account for the increase in navigation flow support.