A series of early April storms brought more water than usual to many parts of the Columbia Basin, improving the April-through-September water supply outlook somewhat in the lower Columbia River, and significantly in the Willamette, Rogue and lower Snake rivers.
In a May 2 webinar, Geoffrey Walters, hydrologist for NOAA's Northwest River Forecast Center, said April rains also brought unusually high runoff in the basin's southern and central regions. Looking at snow measurements, he said, it appears that snowmelt has begun in most areas except along the Montana and Idaho border.
The water supply forecast remains largely unchanged in Columbia River above Grand Coulee Dam--already the driest part of the region, and supply predictions actually dropped in the northern-most regions. The water supply prediction for the Columbia River at Mica Dam in Canada is now down to 89 percent of normal, and dropped in the Kootenai River at Libby Dam to 74 percent of normal.
But many other areas improved.
The forecast at South Fork Flathead River's Hungry Horse Dam is now at 91 percent of normal--up from 82 percent of normal in the April forecast. Both the lower Columbia River at The Dalles Dam and Pend Oreille River at Albeni Falls Dam went from 87 percent of normal on April 3 to 94 percent of normal on May 1.
The lower Snake River saw even more impressive gains, with water supply forecasts at Lower Granite Dam jumping to 115 percent of normal, from 98 percent of normal in April.
"The real eye-popper here is the Willamette and the Rogue," Walters said. At Salem, forecasts now put water supply in the Willamette River at 125 percent of normal, up from 99 percent of normal in April. The Rogue River at Applegate Reservoir expects to have 145 percent of normal water supply, an increase from 121 percent of normal forecast in April.
On April 4, Washington Gov Jay Inslee declared a drought emergency for three central Washington watersheds where water supply is predicted to be well below normal. They include the Okanogan River at 58 percent of normal, the Methow River at 72 percent of normal and the Yakima River at 74 percent of normal. The drought declaration means the state can enact conservation measures and offer support for measures like water leasing or changes to move water through tributaries to support salmon survival.
At a multi-agency drought webinar on April 22, Washington State Climatologist Nick Bond said the drought conditions in most of the Pacific Northwest have eased, but a good portion of Washington is still considered to be abnormally dry, and north central Washington is in moderate drought.
Andrea Bair, with the National Weather Service, said above normal temperatures are predicted for much of the Pacific Northwest over the next three months, and below normal precipitation is "slightly favored," he said.