20-11-11 winter forecast courtesy@.JPG

Six cloud-seeding generators between Hailey and Fairfield expel silver iodide vapor into the atmosphere, reaping additional snowfall for the Wood River Valley.

After lackluster snowpack last winter and a troubling water year in the Wood River Valley, a moderately strong La Niña system could bring cooler, wetter winter weather this time around, forecasters say.

Sun Valley Resort can expect a “great start” to ski season with above-normal precipitation through November, according to Steve Stuebner, forecaster with Idaho Daily Snow.

“It’s pretty amazing just to see the alignment of long-term weather models with short-term forecasts,” he said in an interview. “It looks like we’ll be in the bull’s-eye for getting wetter and colder weather for the next two weeks and beyond.”

Stuebner was referring to the National Oceanic and Atmospheric Administration’s long-term winter outlook—released on Oct. 15—which predicted increased precipitation and colder temperatures in the northern tier of the U.S. Those predictions are tied to La Niña, a weather pattern marked by cooler sea temperatures in the tropical Pacific Ocean.

“I’m feeling optimistic about our upcoming water year with the La Niña,” said Erin Whorton, water supply expert with the Natural Resources Conservation Service, during an Idaho Water Supply Committee meeting Friday.

During the winter of 2016-17, a strong La Niña brought 64 inches of snow to the valley in December and near-record-breaking snowpack in January. Last year, however, both La Niña and its warm-water counterpart, El Niño, were more neutral. In February, north Ketchum received a dismal 0.3 inches of precipitation, according to the NRCS.

“We had some storms coming up from Utah, but a lot of storms coming off the Pacific coast that would normally hit Sun Valley tracked just to the north, to Stanley,” Stuebner said. “Last year was kind of an anomaly. Hopefully, we’ll make up for that this winter.”

Giving Mother Nature a boost

Around 600 snow guns—25 added this year, with Sun Valley’s new Sunrise terrain pod—help create extra snow on Bald and Dollar Mountains every winter by expelling compressed air and water.

What’s perhaps less known is that Idaho Power uses a number of high-elevation generators across the state to “seed” clouds, or extract additional snowfall from winter storms passing through.

Today, six remotely operated generators serve the Wood River Valley—three installed in 2015 and three in 2017, according to Idaho Power Senior Meteorologist Derek Blestrud.

All six generators sit on ridgetops between Hailey and Fairfield and operate from November to April, Blestrud said. Each generator is solar powered and resembles a small cell tower.

The seeding process yields results within half an hour. First, a solution of silver iodide, a naturally occurring compound, is injected over a propane flame at the top of the generator, causing it to disperse into the clouds. Once introduced into the atmosphere, silver iodide particles—just like dust or pollen—give water droplets a structure to freeze around, generating more ice crystals that fall to the ground as snowflakes.

“After silver iodide aerosol comes in contact with super-cooled liquid water, it takes around 30 minutes for snow to fall,” Blestrud said.

It’s unclear exactly how much snow is derived from cloud seeding in the Wood River basin, but Idaho Power estimates that seeding typically boosts snow inventory in the area by 10 percent. Last year, cloud seeding boosted snowpack in the Wood River area by around 6.7 percent. That lower figure can be attributed to 2020’s low water year, drought variances and weaker storm systems, Blestrud said.

Despite what one might assume, cloud seeding can’t create new weather patterns, he said—the process only enhances the natural snow formation process, targeting less-efficient storms.

“If you have a shallow, warmer cloud deck that isn’t forming ice efficiently, that’s when we can go in and turn on the generators to help make that storm a little bit more efficient,” he said.

Email the writer: ejones@mtexpress.com

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