Missouri basin runoff forecast looking better


The latest 2023 calendar year runoff forecast for the Missouri River Basin above Sioux City, Iowa is showing improvement.

“Spring precipitation, including increased mountain snowpack and late season plains snow, has provided improved runoff conditions in the upper basin,” said John Remus, chief of the U.S. Army Corps of Engineers’, Missouri River Basin Water Management Division. “We prefer to see a slower plains snowmelt to improve soil conditions. The longer the snow persists, the greater risk of flooding caused by rapid snowmelt from a spring rain event.”

The 2023 calendar year runoff forecast above Sioux City is 26.4 million acre-feet (MAF), 103 percent of average. The runoff forecast is based on current soil moisture conditions, plains snowpack, mountain snowpack, and long-term precipitation and temperature outlooks.

March runoff in the Missouri River Basin above Sioux City was 1.7 MAF, 57 percent of average.

System storage is currently 46.8 MAF, 9.3 MAF below the top of the carryover multiple use zone.

“Despite these improvements, the System is still recovering from drought, and it will take time to return System storage to the top of the carryover multiple use zone while continuing to serve all Congressionally authorized purposes during 2023,” said Remus.

Basin and river conditions continue to be monitored, including plains and mountain snow accumulation, and System regulation will be adjusted based on the most up-to-date information.

Snowpack

Mountain snowpack in the upper Missouri River Basin improved during March. The April 1 mountain snowpack in the Fort Peck reach was 117 percent of average, while the mountain snowpack in the Fort Peck to Garrison reach was 108 percent of average. By April 1, about 95 percent of the total mountain snowfall has typically accumulated. Mountain snow normally peaks near April 17.

The plains snowpack, which typically melts from mid-February into April, is hanging on longer in 2023 and the plains snow on April 1 showed widespread areas of 4-8 inches of snow water equivalent (SWE) across North Dakota and eastern South Dakota following a blizzard that occurred in late March. The blizzard that occurred April 4-5 in the upper plains was not included in this forecast.

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