The Wood River Valley will need to see a significant boost in precipitation over the next month to meet water demands this summer, a number of hydrologists said during an Idaho Water Supply Committee meeting last Friday.
After “pretty decent” snowfall in January and slightly below-average snow activity in February, hydrologist Danny Tappa of the NRCS-Idaho Snow Survey said the Big Wood basin entered into a dry spell in early March. The region can expect poor spring runoff and water shortages in the summer if that trend continues, he said.
“We’ve hit a flat line,” Tappa said. “At this point, we need about 25% more snow to get to the normal peak, so we’re quite a ways off.”
Precipitation in the basin typically peaks in March and April before dropping off in May and doesn’t usually pick up again until October, according to Tappa.
Tappa noted that the basin also recorded precipitation shortfalls in March 2012 and March 2018, but was able to make up the deficits with late-season snowstorms. Though unlikely, that’s not out of the question for this year, he said.
“We’ve actually seen this happen a few times, with really favorable conditions coming in late March to build the snowpack,” he said. “There’s still the opportunity to gain a fair amount of snow-water equivalent, and one wetter-than-normal month can go a long way.”
Compared to the rest of the state, the Big Wood and Big Lost basins were outliers last month, gaining only one to three inches in snow water equivalent, or the amount of water held in snowpack. (Boise, meanwhile, saw its fifth-snowiest February.) Still, the Big Wood basin fared better than the Big Lost basin, which includes Copper Basin, Mackay and rugged sections of the Pioneers.
“The Big Lost had some nice January gains but a very quiet February. It will need over 40% more snow to reach its average [precipitation] peak, which is kind of a tall order at this stage in the game,” Tappa said. “That’s a lot to make up.”
Both basins are currently experiencing severe-to-extreme drought, according to the U.S. Drought Monitor. “Extreme” drought conditions have continued to develop in northern Blaine County and southeastern Custer County with a center-point near Hyndman Peak, the Monitor shows.
David Hoekema, hydrologist with the Idaho Department of Water Resources, said the Big Lost region is facing a record low runoff volume this spring.
“This is the type of event that happens once every 50 years or so. It’s a pretty extreme condition that is being forecasted,” he said.
Ryan Lucas, a hydrometeorologist with the National Weather Service, agreed.
“We have 50 years of observed volumes in the Big Lost. Our current forecast is lower than any of those volumes, which translates to the second percentile,” he said.
Snow telemetry data from the National Oceanic and Atmospheric Administration seem to corroborate that consensus. On Thursday, the Hyndman Creek SNOTEL station recorded precipitation totals 67% of average. Farther east, the Smiley Mountain station recorded 57% of average. The Chocolate Gulch SNOTEL station north of Ketchum recorded a snow-water equivalent 76% percent of average on Thursday.
Tappa said he’s hopeful that the Big Lost and Big Wood basins will break out of their dry periods this spring. After all, he said, drought has been a persistent issue in both regions since 2019, and agricultural growers have been particularly hard-hit.
“We actually have to go back to the spring period of 2019 to see above-normal precipitation in these areas. This drought goes back many, many months,” he said. “It’s the same old story.”