The updated 2021 calendar year runoff forecast for the Missouri River Basin above Sioux City, Iowa, continues to be below average.
Missouri River Basin Water Management Chief John Remus says, “Both plains snowpack and mountain snowpack continue to lag behind seasonal averages, and soil moisture continues to be much drier-than-normal.” January 2021 runoff in the Missouri River Basin above Sioux City was 1.1 million acre-feet, 141 percent of average.
The above-average January runoff was primarily due to above-normal temperatures melting any accumulated plains snowpack and inhibiting river ice formation. The 2021 calendar year runoff forecast above Sioux City is 22.9 million acre-feet, 89 percent of average. The runoff forecast is based on soil moisture conditions, plains snowpack, mountain snowpack, and long-term precipitation and temperature outlooks.
Mountain snowpack in the upper Basin is accumulating at below-average rates. The January 31 mountain snowpack in the Fort Peck reach was 78 percent of average, while the mountain snowpack in the Fort Peck to Garrison reach was 79 percent of average.