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April 17, 2014
March storms lifted Oregon’s water forecasts
MCKENZIE BRIDGE, Oregon (STPNS) -- “March was a great month for the Pacific Northwest” for the collection of mountain snowpack that will feed the Columbia and Snake rivers and their tributaries this spring and summer, according to Joanne Salerno, a senior hydrologist for the Northwest River Forecast Center.
Precipitation was at or above 150 percent across much of the Columbia basin in March, even soaking areas in southwest Idaho and southern Oregon that still are considered to be amidst severe drought following a dry 2012-2013 season and meager start to the current water year (October-September).
The March storm systems followed wet weather that prevailed in February to balance what had been a relatively dry early winter.
The end result, as the snow-melting season begins, is a cache of stored water that is slightly above average. The expected runoff volume expected to pour down the Columbia past The Dalles Dam from April through September is 95.5 million acre feet, which would be 104 percent of the 1981-2010 average. The Dalles, located on the lower Columbia (river mile 191.5), passes water from the mid and upper Columbia and the Snake and their tributaries.
There, the January - July water volume forecast for is up by 5 percent over the past month, according to the water supply forecast released April 9th by NOAA Weather Service’s NWRFC.
All legs of the water supply stool are above average. The forecast for flows past central Washington’s Grand Coulee Dam is 104 percent of the 30-year average for the January-July period, which is up by 8 percent over the past month. All of the water coming from the upper Columbia in British Columbia, northwest Montana and Idaho flows past Grand Coulee.
The forecast at Lower Granite Dam on the lower Snake River is for 106 percent of average flows, up by 1 percent from the previous month. Southeast Washington’s Lower Granite Dam passes flows from the upper Columbia and such tributaries as the Clearwater, Salmon, Imnaha, Grande Ronde, Owyhee, Malheur and Boise rivers. The Snake, which feeds into the Columbia, typically provides about one-third of the overall Columbia River flow.
The Clearwater, as measured at Spalding in west central Idaho, is expected to produce 122 percent of average runoff, which would be the 10th best total in the past 54 years, according to the NWRFC. The most likely runoff scenario for the North Fork of the Clearwater, as measured at the U.S. Army Corps of Engineers’ Dworshak Dam, is 128 percent of average. The North Fork, and Dworshak’s reservoir, provides cooling flows for the Clearwater and lower Snake in summer that help improve conditions for migrating salmon and steelhead.
The “wettest” runoff forecasts (above 110 percent of the recent 30-year average) are in Columbia River basins draining the Bitterroot Range of Montana, the Rockies, and the Blue Mountains of northeast Oregon.
The April-September runoff forecast for the Kootenai River as measured at northwest Montana’s Libby Dam is 109 percent of normal. The Clark Fork River as measured at Plains, Mont., is expected to see 128 percent of its average runoff this year. The Clark Fork flows into the Pend Oreille in north Idaho, which in turn flows into the Columbia.
April-September runoff forecasts for most areas of the Columbia-Snake river basin are normal to above normal. Forecasts for basins in southeast Oregon, and southwest Idaho, however, are well below normal.
Most forecasts west of the Cascades are near to below normal.
The Clearwater and Salmon drainages as of Wednesday boast snowpacks at 128 percent of average through April 9, according to Natural Resources Conservation Service automated SNOTEL measuring sites. Both rivers flow into the lower Snake River.
The Owyhee and Malheur river drainages, which also feed the lower Snake, were at the bottom of the scale at 64 percent of average “snow-water equivalent” as of April 9th. Both flow across the southeast corner of Oregon into the Snake.
The Deschutes, Crooked and John Day drainages in aggregate has accumulated only about 63 percent of their SWE as of April 9, and the Willamette drainage was at 52 percent of average. Central Oregon’s Deschutes, Crooked and John Day rivers feed the Columbia. The Willamette joins the lower Columbia at Portland.
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