Test flows from Fort Peck Dam to comply with the 2018 Biological Opinion will begin Fri., April 26. The 2018 Biological Opinion requires the test under the Endangered Species Act for operation of the Missouri River Mainstem Reservoir System. The U.S. Army Corps of Engineers will host weekly virtual meetings during the flow test to update the public on test progress and planned operations.

The latest 2024 calendar year runoff forecast for the Missouri River Basin above Sioux City, Iowa shows slight improvement. The 2024 calendar year runoff forecast above Sioux City is 17.5 million acre-feet (MAF), 68% of average. March runoff in the Missouri River Basin above Sioux City was 1.8 MAF, 59% of average. Even with the lower than average runoff forecast the hydrologic conditions are sufficient to conduct a flow test from Fort Peck Dam” said Remus. “The flow test is a requirement of the 2018 Biological Opinion and is meant to determine if there is a Fort Peck Dam water management scenario that could benefit the Pallid Sturgeon.

A warm February led to increased snowmelt and runoff in the Missouri River Basin above Sioux City, Iowa. February runoff was 1.8 million acre-feet, 161% of average with above average runoff in every reach except Sioux City, which was near average. However, the updated 2024 calendar year runoff forecast for the basin continues to be below average.

January runoff in the Missouri River Basin above Sioux City was 0.4 million acre-feet, 56% of average. Runoff was well-below-average due to much-below-normal temperatures over the whole Missouri River Basin and below-normal precipitation over most of the upper basin. The 2024 calendar year runoff forecast above Sioux City is 18.8 MAF, 73% of average. The runoff forecast is based on current soil moisture conditions, plains snowpack, mountain snowpack, and long-term precipitation and temperature outlooks.

As the colder, winter temperatures enter the basin, USACE will closely monitor Missouri River ice conditions between the System reservoirs and downstream of Gavins Point Dam for potential ice jams that could impact river stages and water intakes. Runoff in the upper Missouri River Basin above Sioux City, Iowa, was 1.1 million acre-feet (MAF) during November, 107% of average. The 2023 calendar year runoff forecast is 29.9 MAF, 116% of average. Average annual runoff is 25.7 MAF.

Rainfall in the Missouri River Basin above Sioux City, Iowa, was above normal for August, resulting in above average runoff. However, due previous years' drier-than-normal conditions leaves the total storage in the Missouri River mainstem reservoir system below normal. Based on the Sept. 1 system storage, Gavins Point Dam winter releases will be 13,000 cfs, per the Master Manual criteria. This call focuses on winter release rates and storage at Fort Peck meeting the criteria for a planned Test Flow.

Above average rainfall and fast-melting snow led to above average runoff in the upper Missouri River Basin in June. Runoff above Sioux City, Iowa was 6.7 million acre-feet, which is 122% of average. The annual runoff forecast above Sioux City, Iowa is 29.2 MAF, 114% of average, and about 2.4 MAF higher than last month’s forecast. Precipitation was normal to much-above-normal for the month of June in much of Montana, southern and east-central North Dakota, and western South Dakota. Below-normal precipitation occurred in eastern South Dakota and into the lower Basin.

Warm temperatures in the mountainous region of the upper Missouri River Basin has led to a quick melt of the mountain snowpack. The rapid melting combined with precipitation in the western half of the Basin resulted in above-average inflow into the reservoir system. May runoff for the Basin above Sioux City, Iowa was 4.9 million acre-feet, 144% of average. "The warm temperatures in the northern Rockies has melted the snow earlier than is typical,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division. “With much of the mountain snowpack already melted, the Basin will need additional rainfall to continue the trend of above-average runoff.”

Late season plains snowpack accumulation and subsequent melting led to increased runoff throughout the upper Missouri River Basin during April. For the month, runoff was 4.7 million acre-feet, 159% of average, for the basin above Sioux City, IA. The annual runoff forecast for the upper Missouri River Basin above Sioux City, IA is 26.9 MAF, 105% of average, and 0.5 MAF higher than last month’s forecast. However, soil moisture remains slightly below normal in eastern Montana and the western Dakotas, and well below normal in Nebraska. Even with the plains snowmelt, soils dried out in late April over a large portion of the upper basin.

The updated 2023 calendar year runoff forecast for the Missouri River Basin above Sioux City, Iowa, continues to be below average. The 2023 calendar year runoff forecast above Sioux City is 21.5 million acre feet, 84% of average. The runoff forecast is based on current soil moisture conditions, plains snowpack, mountain snowpack, and long-term precipitation and temperature outlooks. February runoff in the Missouri River Basin above Sioux City was 1.0 MAF, 86% of average.