Missouri River Monthly Update for September. We break down the elements of runoff. After the plains snowmelt and mountain snowmelt, runoff forecasts to soil saturation and rainfall. Rainfall in August provided some welcome inflow into the upper Missouri Basin Reservoir System. Several precipitation events occurred during the month, with some areas receiving 400% of normal rainfall. Despite this fact, drought conditions continue, and are predicted to persist and expand throughout the basin in the coming months. John Remus, Chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division