VAIL, Colo. — Cloud seeding experts say their interpretation of data from automated SNOTEL measuring stations suggests that the water content in snow around Vail and Beaver Creek was enhanced by as much as 30 percent during last winter's cloud-seeding operations.
In an annual operations report required by the state, Durango-based Western Weather Consultants says the cloud seeding added 11 to 15 inches to last winter's prodigious snowpack and yielded 11,200 acre-feet of additional water for the Eagle River watershed.
"We … believe that this valuable service of providing additional snow was achieved in a cost effective manner," the report concludes, recommending that cloud-seeding weather modifications proceed on a routine basis each year to help bolster the state's water supplies and to enhance early season skiing at the targeted resorts.
This year's cloud-seeding operations are under way, and Western Weather Consultant's Larry Hjermstad said he's keeping an eye on the wave of incoming storms to determine if it's time to fire up the silver-iodide generators. Low-level wind fields, cloud characteristics, atmospheric temperatures and terrain features all figure into the equation of determining which network of generators will best seed the cloud system during each seeding opportunity. Hjermstad has been seeding clouds around Vail for 36 years.
Hjermstad said the northwest flow that prevailed last winter under the influence of La Niña is ideal for seeding. If conditions are right, the generators remain operational even after the main impulse of the storm has passed, feeding the flow to wring out available moisture. According to Hjermstad, anecdotal observations during this period suggests that the seeding generates small, fine flakes of powder — "the kind of snow skiers like," he said.
Vail and Beaver Creek were pioneers in the cloud-seeding program, but in the past couple of years, those efforts have expanded to include Breckenridge and Keystone (also owned by Vail Resorts), as well as Arapahoe Basin, Winter Park and seven Front Range water providers. The program is permitted and administered by the Colorado Water Conservation Board's weather modification program.
According to Hjermstad, 27 manually operated stations are used to enhance snowfall in the target areas, with locations including Aspen Canyon, Green Mountain Reservoir, Big Gulch, Pebble Creek, Silverthorne, East Vail, Two Elk Creek and Pando. The ground-based generators inject tiny silver iodide crystals into the path of arriving storms. Moisture in the atmosphere condenses and freezes around those nuclei to wring more moisture from the weather systems. Under ideal conditions, the operation may increase precipitation by 15 percent.
To avoid unwanted consequences such as excessive flooding, cloud-seeding operations stop when certain snowpack thresholds are reached, or if avalanche hazards rise to a critical level.