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Early forecast for less than normal runoff in Lake Chelan Basin

Chelan County PUD
News Release
2/1/2009

The Feb. 1 runoff forecast for the Lake Chelan drainage basin is 70 percent of average for the April 1 to July 31 period. Seventy percent of average runoff would result in 367,600 second-feet-day (SFD) or 728,950 acre-feet (AF) of water. This amount would be 70 percent of last year’s actual runoff of 528,009 SFD.  Current long-range forecasts are calling for warmer and drier than average conditions, with less than average snowfall accumulation.               

Moisture content in the soil, also known as soil prime, appears to be average.  Snowpack densities at the above listed sites range from 32-34 percent, which seem high for this time of year.   

The elevation of Lake Chelan on Feb. 1, 2009, was 1089.63 feet above sea level, which is 2.5 feet higher than the expected average under the current operating license and 2.9 feet higher than last year.  The elevation of Lake Chelan is higher than the expected average due to significant rainfall in early November 2008 and mid-January 2009.  A Global Climate Center long-term weather outlook for North Central Washington is predicting warmer and drier than average conditions through winter and spring, with less than average snowfall accumulation. 

Given the current lake level and forecast for warmer and drier than average conditions, generation will likely need to be reduced at Lake Chelan Hydro in February or March to ensure there is enough water for refill.  Seven operating objectives in the Lake Chelan Hydro Operating License, as well as minimum lake elevation targets, are considered when planning generation and refill.

The Northwest River Forecast Center’s Jan. 29 runoff forecast for January to July is 92 percent of average at Grand Coulee Dam, and 87 percent of average runoff at The Dalles.  Runoff forecasts for other local area basins are below average.  The Wenatchee River forecast is for 90 percent of average runoff April to September, and the Okanogan River forecast is for 69 percent of average runoff for the same time period.

At right is a color coded diagram of the Western United States that shows current snow water equivalent in percent of normal.  Note that the three basins in North Central Washington range from 63-  69 percent of normal snowpack.  Also note that only one basin in Washington is above average, in the southwest part of the state, while all other basins in Washington are at or below 88 percent of average