'Water year' off to slow start
January 4, 2014
The bad news is that the Pacific Northwest and its Columbia River basin have only received about 50 percent of average precipitation over the first three months of the “water year” – October 1 through December 30.

The good news is that there is a big chunk of the winter of 2013-14 to come, during which precipitation could soak the soil and fortify mountain snowpacks.

According a report created December 31 by NOAA National Weather Service’s Northwest River Forecast Center, precipitation upstream of the lower Columbia’s The Dalles Dam from October 1 through December 30 was 50 percent of the 1971-2000 average. The Dalles, located at Columbia River mile 191.5 along the Oregon-Washington border, passes water from the Snake River basin and the upper Columbia.

Early season precipitation totals, as a percent of average, were lowest in the Snake River basin. The precipitation totals since October 1 were 43 percent of the 30-year average as measured upstream of the lower Snake’s Ice Harbor Dam. Ice Harbor, in southeast Washington, channels flows from the upper Snake in Idaho, Wyoming and Utah as well as lower river tributaries such as the Malheur-Owyhee-Boise river basins, the Clearwater and Salmon from central Idaho and the Grande Ronde River basin, which is nested in northeast Oregon.

Ice Harbor is the last of four lower Snake River mainstem dams before the river joins the Columbia in southeast Washington.

The upper Columbia River basin, in British Columbia, northern Idaho and northwestern Montana has been blessed with more plentiful precipitation, though the totals are still well below average.

The Columbia River basin upstream of southern British Columbia’s Arrow Dam has received 71 percent of its average precipitation so far this water year. Tributaries include the Clark Fork (42 percent of average from Oct. 1-Dec. 30), Flathead (64 percent), Pend Oreille in Canada above Waneta Dam (53 percent), Kootenai (68 percent) and Spokane River basin (65 percent).

Precipitation so far in the water year in the Columbia River basin upstream of central Washington’s Grand Coulee Dam has been 62 percent of average. Grand Coulee passes water from the above-mentioned upper Columbia region.

Precipitation has been scarce in western Oregon and Washington with October-December totals ranging from 21 percent of average (Rogue-Illinois basins in Oregon) to 58 percent in northwest Washington’s Snohomish River basin. The Willamette River basin upstream of Portland has received 42 percent of its average precipitation.

Temperatures in the Columbia River basin over the past few months have generally been below normal, according to data posted online by the NWRFC.

Snowpacks, though in the early building stages, are at or above average for this time of year in some of those northern Columbia areas. The Kootenai River basin’s Montana geography has 96 percent of its average snowpack for December 31, according to Natural Resource Conservation Service’s Columbia River Basin SNOTEL snow/precipitation update report. The Kootenai originates in Canada and flows south into Montana, westerly into the Idaho Panhandle and then north before joining the Columbia in British Columbia.

Montana’s Flathead River basin had 115 percent of its average snowpack snow-water equivalent through December 31 and the upper Clark Fork basin had 109 percent.

West-central Idaho’s Clearwater River basin had snowpack at 84 percent of average through December 31. The Clearwater feeds into the lower Snake River.