Kim Fundingsland/MDN Inflow expectations into Lake Sakakawea have declined slightly due to limited rainfall throughout the Upper Missouri Basin.

A reasonably dry July over much of the Missouri River Basin has resulted in a downward revision of expected runoff. Below-normal precipitation in Montana and Wyoming is cited as the reason why.

“Reservoir inflows in July declined due to the warmer and drier conditions in the upper basin. The 2020 calendar year runoff forecast has been reduced slightly due to this declining inflow,” said John Remus, chief of the U.S. Army Corps of Engineers Missouri River Basin Water Management Division in Omaha, Neb.

The change in the August projected runoff outlook is down only 0.3 million acre feet from the July outlook, a drop from 31.2 maf to 30.9 maf. However, even with the decrease, the total projected runoff remains well above the long-term average of 25.8 maf.

Lake Sakakawea ended the month of July somewhat less than the earlier outlook of 1,844.9 feet. As of Monday the state’s largest reservoir was at 1,832.71 feet. Current estimates are that Lake Sakakawea will drop to 1,841.5 feet at the end of the month. With the peak inflow already having passed through the reservoir, a gradual decline in water level is projected to continue with a target of 1,836.4 feet at the end of February 2021.

The long-range precipitation outlook issued by the Climate Prediction Center for Aug.-Oct. calls for an elevated chance of greater than normal precipitation over all of North Dakota and a portion of eastern Montana. Even if that proves correct however, barring major rainfall, the impact on the upper three reservoirs in the Missouri River system, Fort Peck in Montana, Lake Sakakawea, and Lake Oahe in North and South Dakota, may not change significantly.

Current reservoir levels on the Upper Missouri are considered to be well within normal summer operating levels.