Report says last winter’s efforts added more than 8,000 acre-feet of water, recommends routine seeding
By Bob Berwyn
SUMMIT COUNTY — Cloud-seeding experts say their efforts boosted snow totals at Summit County ski areas by 12 to 22 inches last winter, producing an additional 8,850 acre-feet of water in the Blue River Basin.
“We … believe that this valuable service of providing additional snow was achieved in a cost effective manner,” says a report filed with the state by Western Weather Consultants, 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, the $274,000 central Colorado mountains program includes seven Front Range water providers and four ski areas: Arapahoe Basin, Keystone, Winter Park and Breckenridge, all contributing to the cost of the cloud-seeding program, according Joe Busto, head of the state’s weather modification program. The CWCB supports the program with grant funding.
Cloud seeding started this week, and Larry Hjermstad, of Durango-based Western Weather Consultants, 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 said the northwest flow that prevailed last winter under the influence of La Niña is also ideal for seeding. If conditions are right, the generators remain operational even after the main impulse of the storm has passed, feeding the moist 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.
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.
The report estimates that last winter’s cloud-seeding between early November and early February resulted in an additional 12 inches of snow at Breckenridge, 16 inches at Keystone and 22 inches at Arapahoe Basin.
“We believe it’s a worthwhile effort,” said A-Basin COO and general manager Alan Henceroth, adding that the ski area will participate in the program again this winter. Henceroth said it’s hard to tell from casual observations whether the cloud-seeding has a day-to-effect. Given the overall weather pattern, last year would have been a good snowfall year with or without cloud seeding, he said.
A-Basin reported its second snowiest winter on record, going back to the early 1970s. April snowfall (87 inches) broke the all-time record for the month, after cloud seeding had ended for the season.
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. For example, seeding operations in Summit County were suspended last winter during a pre-Christmas storm because of the high snowpack in the area.
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