Basin water forecast near normal
March 8, 2014
The snowy blanket that builds in winter and feeds Columbia River rivers and streams through spring and summer has shown a much desired growth spurt thanks to a wet February and continued precipitation in early March.

The NOAA Weather Service’s Northwest River Forecast Center says that, in the most likely scenario, water runoff from British Columbia, Montana, Idaho, Oregon and Washington this January-July will combine to provide 98 percent of the average volume as measured at The Dalles Dam on the lower Columbia. The forecast is compared to the 1981-2010 average. It takes into account projected flows from the upper Columbia and the Snake River.

That forecast, 93.3 million acre feet, is up by 16 percent when compared to an early February forecast. After low precipitation totals in October-January, a Feb. 1 forecast estimated that only 75.6 MAF would run past The Dalles during January-July.

Precipitation totals across the Columbia-Snake river basin were for the most part at or below 50 percent of average for the October-January period.

But storm clouds flooded in. The area upstream of the mid-Columbia’s Grand Coulee Dam had 24, 86, 61 and 63 percent of average precipitation during the first four months of the water year, which began Oct. 1, 2013. In February precipitation in the upper Columbia was 133 percent of average, and during the first five days of March precipitation was 426 percent of the 30-year average.

The precipitation totals above The Dalles were 149 percent of average in February, and 380 percent of average for the first five days of March. Wetter yet was the Snake River basin, which saw 163 percent of its average precipitation in February in the area upstream of Ice Harbor Dam, located in southeast Washington on the lower Snake. Precipitation in the Snake region, mostly in southern Idaho, was at or below 50 percent of average in October-January.

The most likely scenario as described in the NWRFC’s March 6 forecast is for January-July runoff past the lower Snake’s Lower Granite Dam at 105 percent of the 30-year average. That’s up 17 percent from a forecast made one month earlier. That forecast is made based on current conditions (precipitation, snowpack snow-water equivalent, soil moisture content, runoff to-date and other factors). It includes a 10-day weather forecast.

The Clearwater River basin is loaded. The January-July runoff forecast, as measured at Spalding, Idaho, is expected to be 124 percent of average, which is up 19 percent since the early February forecast. The Clearwater flows into the lower Snake along the Idaho-Washington border.

The forecast for the upper Columbia area above central Washington’s Grand Coulee Dam is 96 percent of the 30-year average runoff volume. That forecast is up by 12 percent since early February.

The snow-water equivalents in snowpacks in western Montana and north Idaho are at or above average. In Montana drainages feeding the Kootenai River, SWE measurements taken at Natural Resources Conservation Service SNOTEL sites are at 109 percent of average as of March 6. That’s up from 92 percent of average for Feb. 15. The Flathead drainage has 124 percent of its average SWE through March 5; the upper Clark Fork 144 percent, the Bitterroot 152 percent, the lower Clark Fork 126 percent and the Idaho panhandle 103 percent.

The March 5 NWRFC forecast pegs Kootenai River runoff for April-September, as measured at Libby Dam in northwest Montana, at 97 percent of average.

Central Idaho’s Clearwater and Salmon river drainages has 121 percent of their average snowpack SWE as of March 5 and northeast Oregon rivers that flow into the lower Snake, such as the Grande Ronde, Imnaha, Powder and Burnt, had 99 percent of average snowpack.

April-September water volume forecasts for most rivers feeding into the Columbia and Snake are normal to above normal for this time of year, according to the NWRFC. Forecasts for basins west of the Cascades, southeast Oregon, and southwest Idaho are below normal.

The runoff forecast for southwest Washington’s Cowlitz River, as measured at Castle Rock, is up by 6 percent from a month earlier, but still only 84 percent of normal for the April-September period, according to the Wednesday forecast. The runoff forecast for the Willamette River at Salem is 90 percent of average, up 4 percent since early February.

The Bureau of Reclamation's March 2014 Total Water Supply Available forecast for the Yakima Basin issued Thursday indicates that there will be a full water supply for both senior and junior water rights this coming irrigation season. The Bureau operates numerous dams in the Columbia-Snake basin from hydro production, irrigation and other uses. Dams operated by both the Bureau and the U.S. Army Corps of Engineers are also operated with the goal of improving survival of migrating fish species such as salmon.

"We are currently expecting the water supply to be near normal," said Chuck Garner, Yakima Project River Operations supervisor. "February snowfall was incredible with a nearly continuous stream of storms hitting the Cascades throughout much of the month. In February, the snowpack went from 54 percent to 95 percent of average in the upper basin and from 63 percent to 97 percent of average in the lower basin.

“This points out that the remaining spring conditions can have a significant impact on the eventual water supply this season."

Reclamation will issue water supply forecasts monthly through July. Specific water delivery levels will not be determined until later in the year after reservoir storage begins to decline.

The March TWSA forecast is based on flows, precipitation, snowpack, and reservoir storage as of March 1, along with estimates of future precipitation and river flows. Other future weather conditions that determine the timing of the run-off and the demand for water are also critical in determining streamflows, prorationing, and the extent to which the reservoirs fill.

"The Yakima Basin weather outlook is favorable and the reservoir system storage on March 1 was a healthy 110 percent of average," Garner said. "We expect the reservoirs to fill and the runoff to provide for early season demands."

In the event that spring precipitation and runoff are unfavorable, Reclamation still expects an adequate supply. Since weather conditions can be unpredictable at times, Garner recommends that water conservation always be a consideration in the Yakima Basin.

For more information, visit http://www.usbr.gov/pn/hydromet/yakima

Bureau reservoirs in southern Idaho for the most part have “big holes to fill” after steep drawdowns last summer, according to the Bureau’s Ted Day. But relatively ample snowpacks should allow most to refill, though Anderson Ranch in the Boise River system could be in question.

But, after shortages last year, “it’s likely we’ll have adequate water to make it through the irrigation season” with minimal rationing, Day said.

The Owyhee and Malheur river basins have been little helped by February and March storms. The two rivers’ are “still pushing near record low snowpack,” Day said. According to SNOTEL data, the two basins are at 57 percent of average SWE for this time of year.

The lowest SWE in the Columbia basin through midweek was western Oregon’s Willamette River at 50 percent. Oregon’s Deschutes-John Day-Crooked river region is at 63 percent of average SWE.