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Lake Chelan Basin runoff forecast drops to 67 percent

Chelan County PUD
News Release
3/9/2009

The March 1 runoff forecast for the Lake Chelan drainage basin is 67 percent of average for the April 1 to July 31 time period. Sixty-seven percent of average runoff would result in 351,800 second-feet-day (SFD), or 697,700 Acre-Feet (A.F.) of water. Current long range forecasts are calling for generally average or above average precipitation in March, decreasing to average or somewhat below average in April and May. Near term temperatures are forecasted to trend toward average, with slightly warmer than average temperatures later in the spring. This is somewhat different than last month, when forecasts called for less than average snowpack accumulation in March. 

Average snow water equivalent at the above listed sites is 68 percent of average. Snowpack densities range from 33 percent to 35 percent, which is slightly below average and approximately the same as last year. Moisture content in the soil (soil prime) appears to trend toward average. 

Snowpack throughout the Northwest is below average. Three North Central Washington basins are reporting snowpack of 62 prcent to 68 percent of average. At right is a color-coded diagram of the Columbia River Basin which shows current snow water equivalent in percent of normal. 

The elevation of Lake Chelan on March 1, 2009, was 1,087.6 feet about sea level, which is 1.9 feet higher than the expected average under the new license and 3.9 feet higher than last year. Less than average snowpack means there will likely be less than an average amount of water for refill, so the lake cannot be drafted as low as might be done in an average snowpack year. 

The generation forecast for Lake Chelan is not optimistic. Generation is currently scheduled at 4 megawatts for all hours, which is the current minimum turbine capacity, in order to provide flow in the tailrace for salmon eggs. Generation is expected to remain at the minimum level, until either snowpack improves and/or the lake elevation increases enough to warrant increased generation. The lake elevation and generation are being managed to meet Operating License objectives and target elevations. The Operating License target elevation for July 1 is 1098 feet.

The Northwest River Forecast Center’s March 2009 Final Runoff Forecast for the Columbia River at Grand Coulee is 87 percent of average for January to July. At The Dalles, the runoff forecast for January to July is 80 percent of average. Runoff forecasts for other local area basins are also below average. The runoff forecast for the Wenatchee River is 73 percent of average April to September, and the runoff forecast for the Okanogan River is 59 percent of average for the same time period.