We closely monitor Washington’s water supply in partnership with other agencies and organizations. Our state’s water supply includes rivers, streams, lakes and springs, and groundwater. These sources provide drinking and irrigation water, fish habitat, and other important benefits.
Here's our latest report on statewide water supply conditions.
Watching the water supply
Conditions as of April 10, 2018
Continued cold, snowy weather during late winter is good news for this summer’s water supply. Washington’s snowpack is near or above normal for this time of year; the statewide average is 119 percent of normal.
The lower Columbia region — consisting of the Cowlitz, Lewis, and Washougal watersheds — recovered to 108 percent of normal from 88 percent in late February. The upper and lower Yakima River basin are at 101 and 103 percent of normal, respectively. The Olympic Mountains (119 percent of normal), north Puget Sound (124 percent of normal), and upper Columbia basins (143 percent of normal) all have healthy snowpack.
Earlier water supply forecasts contemplated lean snow levels in the Walla Walla basin, but heavy March snow improved the basin-wide snowpack to 111 percent of normal. The lower Snake River snowpack is particularly flush at 124 percent of normal.
As we begin both early spring and irrigation season, there is ample mountain snowpack and cool temperatures forecasted by the Climate Prediction Center (CPC) for the immediate future. One area of minor concern is that the snowpack is nearing its saturation point and heavy precipitation may initiate faster melt off.
Precipitation at mountain SNOTEL sites since the beginning of the water year is 112 percent of normal. Puget Sound headwaters stations range from 105 percent of normal at Stampede Pass to 140 percent of normal at Huckleberry Creek. Both the upper and lower Yakima basins are at 108 percent of normal for precipitation.
Statewide precipitation over the previous 30 days is slightly below normal in western Washington and average in eastern Washington. The last seven days, however, have been near or above average for the state (including non-mountain areas).
The CPC precipitation outlook for the near term is for above-normal precipitation and near-normal precipitation for the remainder of spring.
The U.S. Drought Monitor has, for the time being, upgraded portions of Yakima and Klickitat counties in south central Washington to “none,” as in no data suggesting drought. Most states to the south of Washington are experiencing some drought, ranging from Abnormally Dry to Exceptional Drought in Oklahoma (D4).
Temperatures in Washington have been near normal statewide, averaged over the previous 30 days. The CPC forecasts below-normal temperatures for both the next two weeks and normal temperatures for the remainder of spring. Cooler temperatures aide the water supply outlook by regulating the rate snow melts and discharges into rivers.
Looking ahead to this summer, both the Natural Resources Conservation Service and National Weather Service are forecasting that we are likely to have normal to above-normal water supplies this year. For water supply purposes, the April to September runoff period is critical because this is when water demand is highest but precipitation is lowest, hence our scrutiny of snowpack and reservoir levels. This year, forecasted runoff for this period is above 100 percent of normal in all but one or two locations. Some locations in the upper Columbia River basin (e.g., Kettle, Okanogan, and Methow rivers) have forecasted runoff in excess of 125 percent of normal. We’ll continue to keep tabs on streamflows through the spring and summer.
Irrigation and storage reservoirs
In the Yakima River basin, the U.S. Bureau of Reclamation operates five reservoirs to store water for agriculture irrigation and fishery purposes. At this point, total system storage (all five reservoirs considered together) is 118.4 percent of average or about 818,000 acre feet. Total storage capacity is about 1.07 million acre feet. The bureau has forecasted that they will be able to get 100 percent of water supply to users of their water this year. The bureau will update its forecast in early May.
On the west side, the City of Seattle stores water on the Cedar and South Fork Tolt rivers. Snowpack is continuing to build and is above the long-term median for this time of the year. Snowpack in Seattle’s mountain watersheds typically reaches peak accumulations around the first week of April. Storage is also above long-term median conditions.
Beginning-of-month storage conditions for other reservoirs in Washington state are available at the NRCS interactive mapping tool.