Bolstered by a Snake River Basin snowpack that is one and a half times average, spring runoff is expected to be substantial enough to fill Jackson Lake and Palisades Reservoir to their brims.

While temperatures of late have been above average and the sun has been shining, the big melt is still a few weeks away, said Mike Beus, who manages water for the Bureau of Reclamation’s Upper Snake River field office.
3 Creek – In Story Quarter – 50k

“At the lower elevations, runoff is well underway,” Beus said, “but for the areas of the snowpack that significantly contribute to our water supply, I would say we’re at least three weeks off.”

Snake River gauges Monday showed flows of 1,500 cubic feet per second at Moose and 2,400 cfs at the confluence with Flat Creek. The readings are within 10 percent of the long-term median.

Beus said he anticipates high water to begin mid to late May and to last through the end of the following month.

“I would expect high flows for the full month of June,” he said.

Peak flows through the valley, which are difficult to forecast, will depend more on spring and early summer temperatures than on discharge levels out of Jackson Lake this year, Beus said.

Jackson Lake and Palisades Reservoir were between 29 and 31 percent full Monday, bureau monitors show. Palisades, which bottomed out at nearly empty last fall, has been partially drained in recent weeks ahead of high water and heavy inflows, Beus said.

Both bodies of water, which together store more than 2 million acre-feet, should be completely full by the time the rivers subside in summer, he said.

The deep snowpack that will feed them — 148 percent of average as of Monday — is “just at the high edge of the ideal range,” Beus said.

“It’s hard to ensure it doesn’t flood, but we’re in good shape,” he said. “The tributaries can always get us, even in a low [snow] year, with a timely thunderstorm.”

This article appeared in the Jackson Hole News & Guide on April 22, 2014.