September precipitation was once again below average in the Missouri River Basin as drought plagues much of the western half of the nation. September runoff in the Missouri River Basin above Sioux City, Iowa, was 0.8 million acre-feet, 67 percent of the long-term average. Soil conditions in the upper Basin continue to be very dry. Approximately 88 percent of the Missouri River basin is currently experiencing some form of drought, which is a six percent increase from August. The Army Corps of Engineers expects runoff to remain low through the remainder of the year. The 2021 calendar year runoff forecast for the upper Basin, updated on October 1, is 14.8 million acre-feet, 57 percent of average. Average annual runoff for the upper Basin is 25.8 million acre-feet. If realized, the runoff amount would be the tenth-lowest runoff in 123 years of record-keeping. The Corps of Engineers maintains that navigation flows will be supported through December 1.
