Reclamation: Runoff to linger later
High water in Jackson Hole isn’t expected to bust any charts this spring, and water managers anticipate that a slightly above-average runoff season will come on the later side.
The reason isn’t because there is a ton of mountain snow to melt — rather, it’s been too cold to get the job done, said Brian Stevens, water operations manager for the Bureau of Reclamation’s Upper Snake Field Office.
“This year, the cold temperatures have been there for all of February and all of March,” Stevens said, “and the forecast for the next 10 days still shows cold, even though it’s also wet.”
Major runoff into the Snake River watershed, he predicted, won’t pick up until late April and will peak in early June, two weeks later than last year and slightly later than average, he said.
Although there is a well-above-average snowpack in the valleys as a result of the cold, what’s in the mountains most influences runoff. As of Monday, the water weight of the snowfields that feed the Snake River averaged 108 percent of the long-term median.
“It’ll be a medium flood-control year,” Stevens said, “not a huge one.”
As a result, the Bureau of Reclamation isn’t emptying Jackson Lake to anywhere near its natural level to clear space. About 775 cubic feet of water per second has been pouring through the dam since early March, and Stevens expects a continuation of the long, slow draw down for the next couple weeks.
“In 2017, right now we were at 3,500 [cfs] at Jackson Lake,” Stevens said. “Last year, we didn’t make a move until April 4. We will probably be at least a week to 10 days after that.”
Stevens expects a peak release rate in the 3,500 to 4,000 cfs range, likely somewhere in late May. For comparison, water coming out of Jackson Lake topped out at 6,500 cfs in 2017 and 7,200 cfs in 2018. Bureau of Reclamation models forecast a summer release rate of around 2,200 cfs, which is about 10 percent below the historical average.
Stevens and other federal water managers will meet with the public in Jackson for their annual operations meeting at 5:30 p.m. May 23 at the 49’er Inn and Suites.