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.
Watching the water supply
Feb. 22, 2018
Recent cold, snowy weather is good news for this summer’s water supply. Washington’s snowpack is now back above normal for this time of year; the statewide average is 102 percent of normal.
Generally speaking, conditions are better in the northern half of the state than the southern half — and this pattern is especially stark when looking at the West in its entirety. Our neighbors to the south in Oregon, California, and the Southwest are experiencing dire snowpack conditions.
The lower Columbia region — consisting of the Cowlitz, Lewis, and Washougal watersheds — is 88 percent of normal. The upper and lower Yakima River Basin are at 92 and 94 percent of normal, respectively. The Olympic Mountains and upper Columbia basins (Wenatchee, Methow, and Okanogan) all have healthy snowpacks.
The most concerning basin in the state is the Walla Walla watershed, which stands at 77 percent of normal. Snowpack in the Blue Mountains, which supplies runoff to the Walla Walla watershed, usually peaks in mid-March, so it is unlikely snowpack will reach normal conditions there this year.
As measured at mountain SNOTEL stations, statewide average precipitation since the beginning of the water year is 117 percent of normal, but this is not evenly distributed. Lower-elevation regions in southwest Washington (the Chehalis Basin) and along the east slope of the Cascades are showing a precipitation deficit. Indeed, the U.S. Drought Monitor is now depicting portions of Yakima and Klickitat counties in south central Washington as being in a category of D0, or Abnormally Dry.
Much of our precipitation manages to find its way into our groundwater and top soil. Statewide soil moisture is above normal for most of the state. But there are some areas where soil moisture is lagging.
Recent snowfall demonstrates the dramatic change from warm to cold temperature patterns over the past week. The change is especially welcome in the Yakima River Basin, which experienced consecutive days in the upper 60s earlier this month, breaking and tying some daily records.
Looking ahead to this summer, both the Natural Resources Conservation Service and National Weather Service are forecasting that we are likely to have normal water supplies this year. The Walla Walla River is forecasted to have an above-normal volume of April to September runoff, in spite of below-normal snowpack. This is likely due to above-normal basin precipitation and healthy soil moisture. Because forecasts will change as conditions evolve as we get closer to the April to September forecast period, streamflows bear keeping a close eye on.
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 137 percent of average or about 785,000 acre-feet. Supplementing this storage is the so-called sixth reservoir of the Yakima Basin: the snowpack. The National Snow Analysis estimates that the total volume of snow water equivalent in the Yakima Basin now exceeds 2 million acre-feet of water. The Bureau of Reclamation will release an official water supply forecast on March 8.
On the west side, the City of Seattle stores water on the Cedar and South Fork Tolt rivers. Combined reservoir storage is above average for this time of year although snowpack is slightly below normal in the respective watersheds. Precipitation has been above average since the beginning of the water year.
Beginning-of-month storage conditions for other reservoirs in Washington state are available at the NRCS interactive mapping tool.
- Maps and graphics - See SNOTEL, precipitation, drought monitor, temperature,and storage data.