MOUNT VERNON, Wash. — Large winter storms in Washington elevated the statewide snowpack from 75 to 90 percent of normal in less than two weeks.
It bodes well for summer irrigation but may not last without good maintenance storms over the next seven weeks, when warmer and drier weather is forecast, says Scott Pattee, state water supply specialist for the Natural Resources Conservation Service in Mount Vernon.
Feb. 8-14 storms dumped a foot or more of snow in the Blue Mountains, Washington Cascades and much of Eastern and Western Washington. Some other areas received 8 to 10 inches, Pattee said.
But it was light, dry snow so the snow-water content is less that people might think, he said. For example, he said, snow depth at Stampede Pass is 120 percent of normal while snow-water content is 66 percent of normal.
Snoqualmie Pass received 31.5 inches of snow on Feb. 12, a 24-hour record. About 96 inches — 8 feet — fell at the pass over the week and caused a 60-hour closure of Interstate 90.
“The big surprise to weather forecasters was the amount of snow in lowlands of Western Washington,” Pattee said. “It was an unexpected blast of cold air out of Canada.”
Some mountain locations didn’t get as much snow as the lowlands, he said. Two SNO-TEL — snow telemetry — sites south of Mount St. Helens recorded 56 inches of snow in four to five days, he said. That area needed it because the snow level had been very low, he said.
SNO-TEL sites at Lyman Lake, northwest of Lake Chelan, and Harts Pass, farther north in the Okanogan, each recorded about 2 feet, Pattee said. They are at 5,980 and 6,490 feet elevation, respectively.
Snow water equivalent snowpack by basin percent of normal on Feb. 18 versus Feb. 4: Spokane, 95 v. 83; the upper Columbia (Okanogan and Methow rivers), 94 v. 92; central Columbia (Chelan, Entiat and Wenatchee), 92 v. 85; upper Yakima, 81 v. 69; lower Yakima, 99 v. 84; Walla Walla, 119 v. 115; lower Snake River, 105 v. 92; lower Columbia, 86 v. 64; south Puget Sound (from Cascade crest to lowlands), 91 v. 68; central Puget Sound, 75 v. 56 north Puget Sound, 86 v. 84; the Olympics, 90 v. 79.
The Yakima Basin’s five mountain water reservoirs were at 499,188 acre-feet on Feb. 18, which is 47 percent of capacity and 89.4 percent of normal for this time of year. It takes most of the reservoirs’ 1 million-acre-foot capacity and 700,000 acre-feet of water from the mountain snowpack to meet the basin’s annual summer irrigation needs for 464,000 acres of farmland.