Despite warmer temperatures that have limited snowpack build in parts of the Pacific Northwest, government hydrologists predict a healthy water supply during the April-to-September runoff season.
"Last year we had storm track after storm track cross the southern tier, [with] lots of low-elevation snow, lots of precipitation," Northwest River Forecast Center hydrologist Steve King said during a Feb. 1 water supply briefing. "It's a different picture this year. … Our mountain areas across the basin have been warm in general for the season."
Despite the year-over-year change in weather, King said that snowpack looks healthy across the northern portion of the basin, noting that roughly 60% of the Columbia Basin water supply comes from Canada and western Montana.
"From that standpoint, [snowpack is] pretty healthy, generally above normal, and in some cases a fair bit above normal," King said. "[In the south last year], we were very healthy with our snowpack, particularly our low-elevation snowpack. … But we don't have that condition at all right now."
King said current runoff conditions are "pretty wet at the moment. … What might be sticking to the ground as snow is either running off during the storm event or actually being melted off in some cases."


Data from the U.S. Army Corps of Engineers show that total net generation, at 23 hydroelectric plants across the Pacific Northwest, was 8.2 % higher than the year-ago level and 21.0% higher than the 10-year average as it reached 7.91 million MWh in January. That figure is up 22.7% from December 2017.
In the upper Columbia River Basin, the Grand Coulee Dam, the largest of the region, generated 2.21 million MWh, down 2.6% versus the year-ago month but up 17.3% versus the 10-year average for the period. The Chief Joseph Dam generated 1.19 million MWh, down 2.7% versus January 2017 but up 17.0% versus the 10-year average for the month.
January flows in the lower Columbia River Basin were higher versus the year-ago period. Located on the Washington-Oregon border, the Bonneville Dam produced 607,962 MWh, up 14.0% versus January 2017 and 17.6% higher versus the 10-year average for the month. The Dalles Dam, 50 miles downstream, produced 845,284 MWh, up 11.2% from the year-ago month and up 21.5% from the 10-year average for January.

The National Oceanic and Atmospheric Administration Climate Prediction Center's February outlook issued Jan. 31 calls for equal chances of above-normal or below-normal precipitation with above-normal temperatures. On the other hand, the three-month outlook through April issued Jan. 18 calls for above-normal precipitation and below-normal temperatures.
"[That's] something we haven't really seen much of this winter," King said. "So we'll just have to see how that shakes out."
Government forecasts issued Jan. 31 call for April-through-September water supply volumes to be at 109% of normal at the Grand Coulee Dam, up from the prior forecast of 96% of normal.
At the same time, forecast runoff volumes have declined in the southwestern portion of the basin, where smaller hydro dams are located in western Oregon.
California snowpack well below average
The California Department of Water Resources said Feb. 1 that statewide snowpack was 27% of the multidecade average, but state officials remained hopeful future storms could bring the state's water supply higher.
On average, California snowpack supplies roughly 30% of the state's water needs as it melts in the spring and early summer.
"The snow survey today shows water content far below average for this time of year," Chief of the California Cooperative Snow Surveys Program Frank Gehrke said. "Today's measurements indicate an anemic snowpack to date, but there is still the possibility of a wet February and March."
