Seattle's hydroelectric system uses the force of falling water to generate electricity. Water is literally the fuel that runs our generators and City Light power planners pay very close attention to rainfall, streamflows and snowpack.
Northwest power planners work with the "water year" which runs from October 1 through September 30, rather than the calendar year.
The charts below track cumulative rainfall and snowpack in the geographic regions that feed City Light's dams on the Skagit and the Pend Oreille rivers. The dotted line shows the 40-year average. The tan line shows the 2001 water year (October 2000-September 2001), the second-worst drought of the past 75 years. The green line shows the current water year. Both charts are calibrated in water equivalents. While water equivalents do not translate to familiar measures like inches of rainfall, they do allow a numerical comparison from year to year.
For more detail on Washington State hydrologic conditions, go to the US Geological Survey website.