Following a wet March, government hydrologists boosted their water supply outlook for the Pacific Northwest, saying plenty of snowpack remains in the region's higher elevations. Meanwhile, climatologists expect that accumulated snowpack in the Sierra Nevada will boost California's reservoir recovery following five years of drought.
Most of the western U.S.' runoff occurs during the spring snowmelt, the timing and volume of which affects the region's hydroelectric output.
According to the Northwest River Forecast Center, the Pacific Northwest experienced above-normal precipitation with near-normal temperatures, conditions that allowed additional snowpack to accumulate at higher elevations while snowmelt occurred at lower elevations.
Government hydrologist Kevin Berghoff said during an April 6 presentation that the region saw "near or above-record runoff" in March, adding that, at higher elevations, the region's snowpack is "deeper and colder" than it was last year for "near record conditions," especially in the upper and middle Snake River Basin.
The government agency boosted its water supply forecast for the April through September period versus the prior month. Along the Columbia River, water supply at The Dalles dam is projected at 120% of normal, up from the prior month's forecast of 107% of normal, while the water supply outlook for the Grand Coulee dam was boosted to 114% of normal from the prior month level of 102% of normal. Along the Snake River, the Lower Granite dam saw its water supply outlook boosted to 140% of normal from the prior month's outlook of 128% of normal.
Data from the U.S. Army Corps of Engineers show that total net generation at 23 hydroelectric plants across the Pacific Northwest in March was 12.5% above the year-ago level and 29.4% higher than the 10-year average as it reached 8.85 million MWh. That figure is up 25.2% from February.
Year-to-date hydropower production through March totaled 23.22 million MWh, up 16.7% versus the year-ago level and up 22.6% 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 31.3% versus the year-ago month and up 37.8% versus the 10-year average for the period. The Chief Joseph Dam generated 958,488 MWh, down 8.2% versus March 2016 but up 3.0% versus the 10-year average for the month.
March 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 532,403 MWh, down 13.2% versus March 2016 but 0.4% higher versus the 10-year average for the month. The Dalles Dam, 50 miles downstream, produced 787,389 MWh, down 8.5% from the year-ago month but up 7.1% from the 10-year average for March.
'High water' expected in California's rivers during spring snowmelt
Looking to the south, California's state climatologists say the state's snowpack remains healthy despite slowing snow accumulation in March.
"With every monthly measurement of the California snowpack this winter, the state's rebound from the previous five years of drought becomes more evident," a March 30 release from the state's Department of Water Resources said. "Today's electronic readings from 95 sites in the Sierra Nevada show an average statewide snow water equivalent of 45.8 inches, or 164 percent of the historical average for March 30."
"Although the record pace of the snowpack accumulation fell off significantly in March, California enters the snowmelt season with a large snowpack that will result in high water in many rivers through the spring," state climatologist Michael Anderson said.
Chief of the California Cooperative Snow Surveys Program Frank Gehrke said the snowpack, which ranks in the upper quarter of historic snowpacks, is providing "great reservoir recovery."
As of April 6, California's Shasta Lake and Lake Oroville, two of the state's largest reservoirs, were at 91% and 78% of capacity, respectively, holding 4.1 million acre-feet and 2.8 million acre-feet of water.