 However, the runoff above Gavins Point Dam was only 82% of average, with runoff in the Fort Peck to Oahe reaches being approximately 50 to 90% of average. Kevin Lau is a meteorologist with the Weather Service's Missouri River Basin Forecast Center in Kansas City. Lau says part of that increased runoff forecast was due to torrential rains in late June, with some areas south of Sioux Falls, South Dakota, reporting three-day rainfall amounts exceeding 17 inches.