No improvement in Sakakawea forecast

The amount of water in the snowpack over the Missouri River drainage that eventually flows into North Dakota’s Lake Sakakawea has begun to track below normal.

The snowpack plays a major role in determining the annual water levels of the state’s largest reservoir. A below average snowpack almost always results decreased water levels.

The most recent snowpack water content report issued by the U.S. Army Corps of Engineers shows the snow water equivalent in the drainage above Fort Peck Reservoir in Montana is currently 92 percent of average. The drainage above Fort Peck extends all the way to the eastern slopes of the Rocky Mountains.

The drainage from Fort Peck to Garrison, which primarily consists of the flows in the Yellowstone River which joins the Missouri not far from the western end of Lake Sakakawea, is now listed at 84 percent of normal.

The numbers represent a decrease from a mid-December report that concluded the snow water content in the drainage above Fort Peck to be 108 percent of normal and the Fort Peck to Garrison drainage to be 96 percent of normal.

While the snowpack is always a major influence on the amount of runoff that will be received in spring in the Upper Missouri Drainage, a variety of other factors can also have a significant effect on total runoff. Those factors include temperatures, soil moisture and rainfall.

The normal peak of the mountain snowpack occurs near April 15. March and April traditionally produce some of the heaviest snowfall accumulations throughout the drainage, meaning there is plenty of winter remaining to influence potential runoff. Looking ahead, the Climate Prediction Center recently revised their 90-day precipitation forecast for the period of February to April to “equal chance” of normal precipitation over the Upper Missouri Drainage. Previous outlooks had called for a “greater than equal” chance of precipitation through April.

The Corps’ February elevation outlook for Lake Sakakawea is based on runoff totaling 19.9 million acre feet. The January outlook assumed runoff of 20.5 maf. The latest projections, which are subject to change in the coming months, have Lake Sakakawea peaking at 1,831.9 feet in 2013. The level of Lake Sakakawea Tuesday was 1,828.1 feet.

In 2011, Lake Sakakawea exceeded spillway level of 1,854 feet. In 2006 and 2007 Lake Sakakawea dipped below 1,810 feet for several months, creating access problems throughout the reservoir.