Sakakawea outlook increases, Mountain snowpack deepens

As the mountain snowpack water content in Montana continues to rise, so does the amount of runoff expected in the Missouri River basin.

The latest projections from the U.S. Army Corps of Engineers are also reflected in rising expectations for Lake Sakakawea.

The March runoff outlook supplied by the Corps calls for 30.6 million acre feet of runoff into the Missouri River basin. That is a substantial increase over the February 2014 projection of 26.7 maf and more than the forecast at the same period of time during the record runoff year of 2011. Average runoff is considered 26.1 maf.

The March 1, 2011, forecast called for 29.1 maf, less than the current projection. That number rose as snow continued to accumulate throughout the basin. Snowmelt, and heavy rainfall, pushed the total runoff in 2011 to 60.8 maf and sent water cascading over the Garrison Dam spillway for the first time in the history of the reservoir.

Although the current projections appear ominous, there are still several weeks of winter remaining to influence the mountain snowpack in western Montana, which is the primary source of Missouri River water. In the coming days the snowpack could fall either above or below normal as compared to the long-term average.

Currently the mountain snowpack is tracking above 2011 levels over the Yellowstone River basin, generally described as “Fort Peck to Garrison,” and about equal to 2011 levels over the Missouri River drainage. The Yellowstone joins the Missouri above Lake Sakakawea.

According to the Corps, total March 1 snowfall above Fort Peck Reservoir in Montana is 122 percent of the 30-year average and the total snowfall from Fork Peck to Garrison is 133 percent of the 30-year average. Historically, 79 percent of peak snowfall over the Missouri River basin has occurred by March 1 with a normal peak of snow near April 15.

With the latest revelations, Lake Sakakawea is now forecast to peak at nearly four feet higher than what was expected one month ago. The latest projections provided by the Corps says Lake Sakakawea should reach 1,845 feet at the end of July. That compares with a February projected maximum elevation of 1,841.1 feet. Lake Sakakawea’s overflow elevation is 1,854 feet. The reservoir stood at 1,831.5 feet Wednesday.