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Lake Chelan runoff forecast is 93 percent of average

Chelan County PUD
News Release
2/6/2008

The Feb.1 runoff forecast for the Lake Chelan drainage basin is 93 percent of average for the April 1 to July 31 time period.  This 93 percent of average runoff would result in 488,340 second-feet-day (SFD) or 968,380 Acre-Feet (A.F.) of water. This amount would be 81 percent of last year’s actual runoff of 602,240 SFD. Current long range forecasts are calling for above average precipitation and slightly below average temperatures from February through April.  Snotel sites at lower elevations in the basin have a larger percent of average snowpack than higher elevation sites.  The larger snowpack at lower elevations could be an indicator of an early runoff when the weather begins to warm up.

The moisture content in the soil (soil prime) appears to be slightly lower than average due to less than average precipitation during November of 2007.  As the runoff ramps up in the spring some moisture will soak into the ground.  Snowpack densities at the sites listed below average 30 percent, which is average for this time of year and approximately 9 percent lower than last year.

The elevation of Lake Chelan on Feb.1, 2008, was 1086.72 feet, which is 0.4 feet lower than the expected average under the new license and 5.0 feet lower than last year.  There are two reasons the lake is so much lower this year than last.  The main reason is heavy rains and subsequent inflow in early November 2006 increased the lake level by almost 3 feet over a two-week period. This increase in elevation carried through the entire 2006-2007 drawdown and refill period.  The secondary reason is the lake was drawn down approximately 0.8 feet lower at the end of September 2007 than in 2006 due to implementation of the new operating license. Given the current lake level and assuming average precipitation through April there should be plenty of water for refill by July 1. 

The generation forecast for Lake Chelan is optimistic.  If average precipitation and temperatures occur Chelan Hydro will likely be generating at full capacity 24/7 approximately through March of 2008.  After that generation may need to be reduced through spring runoff to ensure refill. 

The Northwest River Forecast Center’s Feb. 1 Early Bird Forecast for the Columbia River at Grand Coulee is 98 percent of average runoff for the January to July period.  At The Dalles the forecast for January to July is 95 percent of average runoff.  Forecasts for other local area basins range from below to above average.  The Wenatchee River is forecast for 104 percent of average runoff April to September and the Okanogan River forecast is for 93 percent of average runoff for the same time period.

Above is a color-coded diagram of the Western U.S. that shows current Snow Water Equivalent in percent of normal.  Note that most Washington sites in the northern Cascade Mountains are slightly above or below normal, while many of the sites in the southern Washington Cascades are a considerable amount above normal.