OMAHA, Neb. –August runoff in the Missouri River Basin above Sioux City, Iowa was 1.0 million acre-feet (MAF), 73% of average. Runoff was well below normal in the Fort Peck and Garrison reaches due to dry soil moisture conditions and areas of below-normal precipitation. Runoff was above normal for the Oahe, Fort Randall, and Gavins Point reaches, and near normal in the Sioux City reach, mostly due to above-normal precipitation during parts of August.
The U.S. Drought Monitor indicates that over 83% of the Missouri River Basin is abnormally dry or in drought conditions. Drought conditions are expected to improve in Colorado, southern Wyoming, and western Nebraska and Kansas by the end of November as El Nino conditions strengthen.
September runoff in the upper Basin is forecast to be well-below average, especially in the Fort Peck and Garrison reaches. The updated 2026 calendar year forecast for the upper Basin is 15.4 MAF, 60% of average. Average annual runoff for the upper Basin is 25.7 MAF.
As of Sept. 1, the total volume of water stored in the System was 47.2 MAF, down 1.3 MAF during August. The updated reservoir studies indicate that the System storage is expected to be 43.8 MAF, approximately 12.3 MAF below the base of flood control, at the start of the 2027 runoff season.
The Fort Peck release will be maintained at 7,000 cfs during the fall months and into early winter. The Garrison release will be reduced from 17,000 cfs to 13,000 cfs starting on Sept. 14.
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