Published 10:54 am Thursday, May 22, 2025
Idaho Power’s 2024-25 cloud-seeding season was quieter than usual as conditions limited opportunities.
All measures tracked were below the 10-year average, according to information that Shaun Parkinson, the company’s water resources leader, presented at a meeting of the Idaho Water Resource Board’s cloud seeding committee.
Total silver iodide used was 34.9% below average in the Idaho central mountains and 27% below average in the Upper Snake River region.
Ground generator hours were below average by 21.7% in the central mountains and by 24.1 % in the Upper Snake.
Aircraft hours were below average by 43.5% in the central mountains and by 23% in the Upper Snake. Flare usage was below average in both regions.
“The season was slow overall for cloud seeding, with limited storm opportunities through much of the season,” Parkinson told Capital Press. “Many of the storms that came through were either too warm to seed or they were already naturally efficient at generating snow.”
Idaho Power seeds clouds by introducing additional ice nuclei — silver iodide — into passing winter storms to increase precipitation. The company uses remote ground generators at high elevation sites or airplanes that burn special flares within clouds to release iodide into storms.
Tiny water particles in the clouds freeze on contact with the iodide and eventually grow before falling as snow. Conditions may be optimal if a storm has abundant vapor or small liquid droplets and appropriate temperatures, according to the company.
Cloud seeding depends on factors including the presence of super-cooled liquid water that is below 32 degrees Fahrenheit but not frozen, appropriate temperatures for seeding to work efficiently, and winds to mix and carry the seeding agent into the storm, Parkinson said.
“Each storm is unique with regard to these conditions,” he said. By using a combination of ground equipment, aircraft burn-in-place and aircraft-ejectable flares, “our meteorologists can target the location of the storm where the temperatures are most conducive to effective cloud seeding.”
Storms wherein temperatures are best near the ground are seeded with ground-based equipment. Storms wherein temperatures are best at higher elevations are seeded with aircraft.
Variation of seeding time — or release of silver iodide — from average for any seeding type “tells us that the seeding conditions were more or less favorable than average,” Parkinson said. “Less than normal can be a result of limited storms or storms that were naturally efficient.”
The 2024 and 2025 winters offered seeding opportunities below the 2015-25 average, he said. Water year 2025 had slightly more aircraft hours than 2024, but less generator runtime and total silver iodide released. Most seeding in the 2025 water year occurred from January through March.
“Less ground seeding in the Upper Snake occurred due to unfavorable winds, meaning winds were too light or not in the direction to carry silver iodide into the target area,” Parkinson said. The seeding season “ended on a strong note in March with near- to above-normal seeding opportunities.”
He compared dry water year 2021 and the unusually wet 2017 to the 2015-25 average.
In 2021, ground generator run times were 127% of average, and silver iodide released was 125%. Aircraft hours were around normal at 101%.
In 2017, generator run times were 77% of average and silver iodide released was 88%, but aircraft hours were 126%.
Below-normal seeding in the heavy winter of 2016-2017 “was due to suspension criteria being met as early as December,” Parkinson said.
The typical cloud seeding season runs from Nov. 1 to April 30, according to Idaho Power.
The Idaho Water Resource Board since 2014 has participated in a collaborative cloud seeding program with Idaho Power and water users in the Boise, Wood and Upper Snake river basins. Idaho Power conducts program operations, and IWRB and local water users provide funding support.
Cloud seeding generates about a 10% annual average increase in snowpack across all basins of operation, according to the board.
Idaho Water Resource Board program details can be found at https://idwr.idaho.gov/iwrb/programs/cloud-seeding-program/
