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Final forecast for Lake Chelan runoff is 75 percent of average

Chelan County PUD
News Release
4/9/2009

The April 1 runoff forecast for the Lake Chelan drainage basin is 75 percent of average for April 1 to July 31.  Seventy-five percent of average runoff will result in approximately 393,825 second-feet-day (SFD) or 780,950 Acre-Feet (AF) of water.                  

Snow survey field data was collected on March 30, 2009.  Snow water equivalents at the above listed sites were collectively 77 percent of average on April 1.  Snowpack densities at the above sites averaged 36 percent on April 1, while historical snowpack densities on April 1 average 40 percent.  Moisture content in the soil appears to be average.  Visual observations during the snow survey indicate a below-average accumulation of low-level snow in selected areas of the Lake Chelan drainage basin.       

Typically runoff begins in early to mid April. Runoff has not yet started this year. On April 1, 2009, the USGS Stehekin River gage reported a flow of 178 cfs, which is 22 percent of average.  One current long range forecast predicts above-average precipitation and below-average temperatures during April and May for Seattle and Spokane.

The elevation of Lake Chelan on April 1, 2009, was 1086.1 feet, which was 2.8 feet higher than last year on April 1.  Generation and spill will be managed with the intent of meeting target elevations, provided early to average runoff timing occurs, and license operating objectives. Chelan powerhouse capacity will be one-half of average from April 1 through at least August, due to modernization of one of the generation units. Spill will likely be needed in June and July to manage lake elevations due to reduced powerhouse capacity.   

The Northwest River Forecast Center’s April 2008 final forecast for the Columbia River at Grand Coulee is 89 percent of average runoff for the January to July period.  At The Dalles, the forecast for January to July runoff is 86 percent of average. Forecasts for other local area basins are also below average. The Wenatchee River forecast is 80 percent of average runoff April to September. The Okanogan River forecast is 59 percent of average for the same period.

On the map at right is a color-coded diagram of the Westwide Snotel Current Snow Water Equivalent in percent of Normal.