U.S. government hydrologists predict a healthy runoff season across much of the Pacific Northwest, but expressed concern about elevated runoff levels for the water year-to-date.
In its latest water supply briefing given on March 1, the Northwest River Forecast Center predicts April-through-September runoff at 115% of normal at the Grand Coulee Dam, located in the Upper Columbia River basin, up from the prior month's forecast of 109% of normal. Government hydrologists expect some Columbia River tributaries to experience runoff levels in the top 10 for the 1971-to-2017 period of record.
During February, northern Idaho, western Montana and the Canadian Rockies experienced above-normal precipitation and below-normal temperatures. Meanwhile, areas to the south experienced below-normal precipitation and slightly above-normal temperatures, leading to lower snowpack levels across the Pacific Northwest's southern tier, especially the southern Cascades.
During the water supply briefing, Northwest River Forecast Center hydrologist Kevin Berghoff highlighted above-normal runoff levels in the upper and lower Columbia River Basin and the Snake River Basin as a cause for concern. "The early runoff is a sure sign that we're losing our snowpack too fast," Berghoff said.
But the National Oceanic and Atmospheric Atmospheric Administration Climate Prediction Center's outlook for March issued Feb. 28 calls for above-normal precipitation and below-normal temperatures, while it's three-month outlook issued Feb. 15 calls for equal chances of above- or below- normal precipitation and below-normal temperatures.
"So there is some hope in the forecast for the snowpack to rebound in areas like Oregon and Idaho," Berghoff said.


Data from the U.S. Army Corps of Engineers show that total net generation at 23 hydroelectric plants across the Pacific Northwest was 14.1 % higher than the year-ago level and 39.4% higher than the 10-year average as it reached 8.06 million MWh in February. That figure is up 2.0% from January.
Year-to-date hydropower production through February totaled 15.97 million MWh, up 11.1% versus the year-ago level and up 29.6% from the 10-year average for the period.
In the upper Columbia River Basin, the Grand Coulee Dam, the largest of the region, generated 2.31 million MWh, up 22.6% versus the year-ago month and up 48.9% versus the 10-year average for the period. The Chief Joseph Dam generated 1.23 million MWh, up 28.0% versus February 2017 and up 45.5% versus the 10-year average for the month.
February flows in the lower Columbia River Basin were also higher versus the year-ago period. Located on the Washington-Oregon border, the Bonneville Dam produced 591,521 MWh, up 10.6% versus February 2017 and 29.1% higher versus the 10-year average for the month. The Dalles Dam, 50 miles downstream, produced 868,968 MWh, up 29.5% from the year-ago month and up 40.3% from the 10-year average for February.

Calif. snowpack below average despite needed storms
Snow surveys conducted by the state of California indicate snow water equivalent in the northern Sierra mountains is 30% of the multi-decade average while that of the central and southern Sierra mountains is 43% and 37% of the multi-decade average, respectively.
"California has unquestionably experienced a dry winter this year, with a near-record dry February," California Department of Water Resources director Karla Nemeth said. "While we're happy to kick off March with this healthy storm, the variability of this winter's weather patterns underscores the importance of continued conservation."
On average, California snowpack supplies roughly 30% of the state's water needs as it melts in the spring and early summer.
