System storage peaked at 68.5 million acre feet (MAF) on July 20. Widespread and heavy rainfall in the upper Missouri River basin (above Sioux City) resulted in another month of above average runoff. Areas of Montana, Wyoming, South Dakota, and Nebraska received two to three times normal precipitation during July.
July runoff in the upper basin was 7.0 MAF, which is 213%of average. The average July runoff is 3.3 MAF. Runoff remained particularly high in the reaches from Garrison Dam in North Dakota to Sioux City, Iowa, which ranged between three to seven times average.