Pacific Northwest hydropower generation rose 1.4% in December 2019 from a month ago, slower than the 39.1% growth from October to November 2019. December 2019 hydro power output also remained below year-ago level and 10-year average, as drier-than-normal conditions prevailed in the region.
Much of the Columbia River Basin received below-normal precipitation in December 2019, with some areas along the northwestern section and a portion of the south experiencing near-to-above normal precipitation, according to the National Oceanic and Atmospheric Administration.
Data from the U.S. Army Corps of Engineers show that total net generation at 23 hydroelectric plants across the Pacific Northwest in December 2019 totaled 5.16 million MWh. It was 2.7% below the year-ago level and 16.7% below the 10-year average.
In the upper Columbia River Basin, the Grand Coulee Dam, the largest of the region, generated 1.48 million MWh, up 0.8% versus the year-ago month but down 16.2% versus the 10-year average for the period. The Chief Joseph Dam generated 824,182 MWh, down 0.4% versus December 2018 and down 13.4% versus the 10-year average for the month.
December 2019 flows in the lower Columbia River Basin were mostly lower versus the year-ago period. Located on the Washington-Oregon border, the Bonneville Dam produced 416,943 MWh, down 0.4% versus December 2018 and 11.1% lower versus the 10-year average for the month. The Dalles Dam, 50 miles downstream, produced 531,693 MWh, down 1.7% from the year-ago month and down 14.4% from the 10-year average for December.
Hydropower production for calendar year 2019 totaled 63.33 million MWh, down 18.1% versus the year-ago level and down 15.4% from the 10-year average for the period.
Early January snowpack below average in Northwest, close to normal in California
Observed snow water equivalent was near to mostly below normal outside of the upper Columbia River Basin on Jan. 8 amid a drier-than-normal water year thus far across the Pacific Northwest, Northwest River Forecast Center hydrologist Geoffrey Walters said in the agency's latest water supply briefing. Snow water equivalent is a measure of the amount of water in the snowpack and an indicator of spring runoff.
Farther south, California's Department of Water Resources, or DWR, said in a Jan. 2 news release that storms towards the close of 2019 helped usher in a "good start" to 2020 snowpack in the Sierra Nevada region. Statewide snow water equivalent was at 9.3 inches on Jan. 2, or 90% of the daily average, after storms in December 2019 drove the state's precipitation level up to 74% of the annual average for this time of year.
Notwithstanding these trends, hydrologists for both the Pacific Northwest and California remarked that precipitation levels in later months could still alter snowpack volume.
Sean DeGuzman, DWR chief of snow surveys and water supply forecasting, said that "[i]t's still too early to predict what the remainder of the year will bring in terms of snowpack." Meanwhile, Walters said, "There is still time for that snowpack to build through a lot of [the Northwest]."
In California, the January-March period has historically accounted for more than half of the winter snowpack building in the Pacific Northwest while December-February brings in three-fourths of annual precipitation.
For the Pacific Northwest, April-September water supply forecasts are generally near normal, buoyed by the 10-day outlook issued Jan. 8 for much wetter-than-normal conditions for the southern portion of region.