The heavy run on the Snake River this year leaves upstream reservoirs full and primes the pump for another good water year in 1998.
Even an average winter’s worth of snow in eastern Idaho and western Wyoming would fill the Upper Snake’s federal reservoir system.
But about two-thirds of southern Idaho’s irrigation water comes from natural runoff, not reservoir storage. So far this winter, mountain snowpacks are under the long-term average for this time of year, said Ron Abramovich, a Boise hydrologist with the snow survey wing of the U.S. Natural Resource Conservation Service.
“We’re looking at a slower start this year than last year,” Abramovich said. “We’re below normal, snowpack-wise, across the entire state, and even the higher elevations in western Wyoming are below normal.”
But he said things can change quickly. “With one storm, we could see the amount of snow and snow-water doubling.”
Runoff from last winter’s heavy snowpack continues to keep the Snake River flowing at remarkably high levels for this time of year.
Confident that upstream reservoirs will fill next spring, water managers with the U.S. Bureau of Reclamation plan to keep releases at Milner Dam at about 6,700 cubic feet per second for the rest of the year. Flows past Milner could rise if storms dump more rain and snow in the high country.
“There’s the potential for it to go up some more in December,” said Mark Croghan, a Burley bureau hydrologist.
“But if December is real dry and it looks like we’re headed into a real dry winter, the releases may go down slightly.”
xxxx Accumulation Under normal circumstances, only 20 percent of an entire winter’s snowfall is on the ground by Dec. 1, hydrologist Ron Abramovich said. By New Year’s Day, about 40 percent of a typical winter’s snow has fallen, and the snow-accumulation season is half over by mid-January.