Water managers and hydrologists are eyeing a below-average Snake River Basin snowpack and say that a dry, warm spring in the forecast presents little hope for a surplus of snow in the weeks ahead.
As of Monday morning, the water content of the snow at 22 SNOTEL monitoring stations scattered around the Snake watershed averaged out at 87% of the long-term median. While that doesn’t depart too far from the norm, it’s a change for a part of the Northern Rockies that’s enjoyed an above-average snowpack for seven consecutive winters.
“Usually, the Snake is always about average or above average, but this year looks like what happened in 2012 or ’13,” said Jim Fahey, a hydrologist for the U.S. Department of Agriculture’s Natural Resource Conservation Service.
At the same date in 2012, the snowpack sat at 96% of the median, while in 2013 the measure registered 83%. A late April snowstorm in 2013 nudged the snowpack up to just above the median, Fahey said, but then it warmed and melted off fast that spring. There’s not much in the forecast to suggest that winter is going to whip back up in 2021.
“The long-range forecasts have been consistent the last couple months, advertising a lower-than-average precip and above-average temps,” Fahey said. “Unfortunately, I just don’t think we’re going to get a lot to add on to this.”
The scarcer high-elevation snows coincide with drought-like conditions downstream in Idaho’s agricultural Snake River plain.
“It is very dry, especially in the irrigation areas,” said Jeremy Dalling, who leads Snake River reservoir operations for the Bureau of Reclamation. “Soil moistures are essentially the lowest they’ve been in the last 10 years.”
Dalling doesn’t yet have a detailed forecast for how he’ll operate Jackson Lake Dam, but he anticipates that peak-runoff release rates will be relatively low and summer releases will be relatively high.
Summer flows at the dam should stay below 3,000 cfs, he said. Because of scheduled maintenance on the dam, Jackson Lake’s water storage will need to be lowered to about 68% capacity by next fall.
Statewide, the snowpack on Monday morning was sitting at 88% of the median. The snowpack in all basins across Wyoming decreased 10 to 15% over the past week as a result of warm weather and scant precipitation. The relatively wettest portions of the state are the Yellowstone and Lower North Platte river basins, while the driest are the Belle Fourche and Cheyenne river basins.