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 million acre feet (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.
The 2019 upper basin runoff forecast is 52.9 MAF. If realized, this runoff total will be the second highest runoff in 121 years of record-keeping, only surpassed by 2011 (61.0 MAF) and exceeding 49.0 MAF observed in 1997. Total upper basin runoff through July 31 was 45.3 MAF, exceeding the total upper basin runoff in 2018 of 42.1 MAF.