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.”