Reservoir inflows in the Missouri River basin above Sioux City, Iowa were well-below average in March, contributing to a below-average forecast for 2021. John Remus, chief of the Missouri River Basin Water Management Division for the Army Corps of Engineers, says, “Due to the lack of plains snowpack in 2021, below-average mountain snowpack, and dry upper basin conditions, we expect upper basin runoff to be below average.” The updated 2021 upper basin runoff forecast is 21.3 million acre-feet, 83 percent of average.
The upper basin runoff forecast is based on soil moisture conditions, plains snowpack, mountain snowpack, and long-term precipitation and temperature outlooks. System storage is currently 56.1 million-acre-feet, at the base of the annual flood control zone. The Army Corps of Engineers says the system is positioned to serve all Congressionally authorized purposes during 2021, including flood control, navigation, and water supply. Gavins Point Dam releases were increased near the end of March to begin flow support for Missouri River navigation.