Fort Peck Reservoir Water Forecast
June runoff in the Missouri River Basin above Sioux City, Iowa was 2.9 million acre-feet, 52% of average. The updated 2026 calendar year runoff forecast for the Missouri River Basin above Sioux City, Iowa, continues to be below average.
“Mountain snowpack peaked much earlier than normal this year and completely melted by the end of June,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division. “June runoff was below-normal to well-below-normal in every reach due to below average precipitation, dry basin conditions and below average mountain snowpack. Dry conditions are expected to continue in July.” The 2026 calendar year runoff forecast above Sioux City is 15.5 MAF, 60% of average, and the same as last month’s forecast. The runoff forecast is based on current soil moisture conditions, mountain snowpack, and long-term precipitation and temperature outlooks.
System storage on July 1 was 49.1 MAF, 7.0 MAF below the top of the carryover multiple use zone. “Based on the July 1 System storage, flow support for navigation decreased from 5,500 cfs below full-service to minimum service,” said Remus. “Per the guidelines in the Master Manual, this will also result in a shortened navigation flow support season ending Nov. 15 at the mouth of the Missouri River. A full navigation support season typically ends Dec. 1. Gavins Point releases were reduced to 24,000 cfs in early July due to recent rainfall and to account for the decrease in navigation flow support.”
“The monthly study indicates that the winter release from Gavins Point, which is based on the Sept. 1 System storage check, will likely be at the minimum rate of 12,000 cfs,” added Remus. Basin and river conditions continue to be monitored, including soil moisture and drought conditions, and System regulation will be adjusted based on the most up-to-date information.
Mountain Snowpack: The mountain snowpack melted quickly due to warmer-than-normal temperatures during the spring and early summer. By June 25, all the snow had melted in both the reach above Fort Peck and the Fort Peck to Garrison reach. The mountain snowpack peaked in the Fort Peck reach on March 16 at 77% of average, while the Garrison reach peaked on March 16 at 79% of average. Mountain snowpack normally peaks near April 17 and melts out in both reaches around July 1. The mountain snowpack graphics can be viewed at: https://go.mil/mr-mtn-snowpack.
Reservoir Forecast
Fort Peck Dam
- Average releases past month – 6,800 cfs
- Current release rate – 7,000 cfs
- Forecast average release rate – 7,000 cfs
- End-of-June reservoir level – 2223.9 feet (up 0.7 feet from May 31)
- Forecast end-of-July reservoir level – 2223.6 feet
- Notes: Releases will be maintained at 7,000 cfs through September.
The forecast reservoir releases and elevations discussed above are not definitive. Additional precipitation, lack of precipitation or other circumstances could cause adjustments to the reservoir release rates.
Hydropower: The six mainstem power plants generated 696 million kWh of electricity in June. Typical energy generation for June is 841 million kWh. The power plants are expected to generate 7.2 billion kWh this year, compared to the long-term average of 9.3 billion kWh. To view the detailed three-week release forecast for the mainstem dams, go to https://go.mil/mr-3wk-fcast.
The Missouri Basin Web App provides links to these reports and others that are updated more frequently. https://go.mil/mr-webapp.
