Abundant early snow in Yampa Valley contributes to storage in Lake Powell

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— Snow is for skiing. But even more significantly, the snow that falls in the mountains surrounding Steamboat Springs every winter is counted on to help fill downstream reservoirs. It supplies irrigators and municipal water systems all the way down the Colorado River Basin and beyond.

It’s early in the season, but the snowpack in the combined Yampa and White river basins that feeds the Colorado River and downstream reservoirs in spring is off to a good start. The snow water equivalent of this year’s accumulated snowfall stands at 121 percent of median for Dec. 12, according to the federal Natural Resources Conservation Service in Colorado. Coincidentally, the snowpack in the overall Colorado River Basin is also at 121 percent this week.

Close to Steamboat, the standing snow on the ground on the west summit of Rabbit Ears Pass equates to 8.1 inches of moisture, or 127 percent of the median 6.4 inches. The snow water equivalent at the Elk River snow-measuring site on the edge of the Mount Zirkel Wilderness Area is 138 percent of average. There is already 13.7 inches of water stored in the snowpack above 10,000 feet on Buffalo Pass, northeast of Steamboat. But that amount is just 96 percent of the median for the date.

And the abundant early snowfall has come on the heels of above-record precipitation in Steamboat in September and above-average precipitation in both October and November.

Katrina Grantz of the Federal Bureau of Reclamation in Salt Lake City, Utah, said Thursday that a wet autumn in the Yampa Valley along with other river valleys that contribute to the Colorado River Basin helped boost water storage in reservoirs.

“Unregulated inflows (to Lake Powell) in September were 210 percent of average,” Grantz said. “It was huge. We came up 2 feet in 10 days in Lake Powell at a time of year when we’re normally decreasing 2 feet.”

Still, it wasn’t enough to reverse course on a year that turned out to be the fourth driest on record at Utah’s Lake Powell. That’s where Colorado stores much of the water it is obligated to send to lower basin states including Nevada, California and parts of several others.

Grantz is a hydraulic engineer who writes monthly updates on conditions at Lake Powell. She said even record autumn rainfalls really can’t offset a poor spring runoff when the melting snow that thunders down western rivers can cause the giant reservoir to rise 40 feet.

However, the abundant rainfall of autumn 2013 can play a role in boosting spring runoff in 2014, according to Grantz. The September precipitation helped to replenish soil moisture after the drought of 2012, which is expected to reduce the amount of the snowmelt that sinks into the ground before reaching the streams and rivers.

“In addition to getting that inflow into Lake Powell and boosting its elevation, we’ve seen improved soil moisture conditions throughout the basin, which means snowpack is more likely to result in runoff than it would have prior (to the rains),” Grantz said.

Soil moisture is taken into account by Grantz and her colleagues when they project next spring’s runoff.

“Even before snow started falling, we were seeing the forecast increase with the models projecting more of the snow would result in runoff,” she added.

Her Dec. 11 report on the status of Lake Powell states that it was 47 percent full at the end of November. Water year 2013 concluded Sept. 30 with inflow volumes into Lake Powell for the 12 months that began on Oct. 1, 2012, at just 47 percent of average.

To reach Tom Ross, call 970-871-4205, email tross@SteamboatToday.com or follow him on Twitter @ThomasSRoss1

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