Cloud-seeding machines strategically positioned in Colorado’s high country have been aimed at the sky for four decades, spewing a compound called silver iodide into the clouds to try to make it snow.



Skeptics have been plenty and definitive research was elusive — it’s hard to prove exactly how much more snow falls after clouds are seeded when no one can say for sure what Mother Nature had planned on her own.



But as Colorado’s drought intensifies and the state grows desperate to increase snowpack, a new study is helping create buzz around cloud seeding. And for the first time, Colorado is stepping up its game and plans to try cloud seeding not just from generators on the ground, but by airplane.



Cloud seeding, or weather modification, is mentioned multiple times in the Colorado Water Plan.

And a drought contingency plan approved this month by half of the seven states that make up the Colorado River Basin coalition includes three key components: reducing water consumption, managing reservoirs and “augmenting” the water supply through cloud seeding and removal of water-sucking tamarisk, or salt cedar trees.

“By itself, cloud seeding is not a drought buster, but it is one proven method to use along with demand management and reservoir operations,” said Dave Kanzer, deputy chief engineer for the Colorado River District, based in Glenwood Springs.

“Revolutionary” research shows cloud-seeding works outside a physics lab

A breakthrough study of cloud seeding by aircraft involving University of Colorado and University of Wyoming researchers took place in 2017 in the mountains of southwest Idaho. It captured attention after its results were published this year in the Proceedings of the National Academy of Sciences. For the first time, researchers — in a second aircraft flying near the cloud-seeding plane — could see silver iodide enter the clouds and form snow crystals.



“We unambiguously can show it works in the atmosphere,” said Dr. Katja Friedrich, a professor of atmospheric and oceanic sciences at CU and one of the study’s authors. “That was very revolutionary.”



In the experiment, funded by the National Science Foundation with support from Idaho Power Co., the cloud-seeding airplane passed through the clouds dropping flares of silver iodide, a compound that attaches to water molecules and forms crystals. The turboprop soaring above the Payette Basin also flared silver iodide from its wings as it flew through clouds rich with supercooled water droplets, ripe for seeding.



The research plane flew near the seeded clouds and was able to record via radar that silver iodide caused the water molecules in the clouds to freeze. The researchers’ radar detected water molecules inside clouds becoming “glaciated” and growing heavier after they were seeded with silver iodide, forming snow.



Now that they’ve proved cloud seeding works, follow-up work is needed to determine how much snow it actually produces and whether it’s an efficient way to increase snowpack, Friedrich said. Cloud seeding in Colorado is a $1.2 million annual operation, and according to the best estimates of researchers, can increase snowfall anywhere from 2 to 15 percent per storm.



“What is the value of water?” she asked. The closest Friedrich could come to answering that question was to say that whatever its value, it’s going up as drought conditions persist.

A cloud-seeding aircraft flies above North Dakota. Silver iodide is dropped into supercooled, liquid-filled clouds by flare. (Photo provided by Weather Modification International)

Seeding the clouds by aircraft above northern Colorado

A turboprop plane, a King Air C90 owned by Weather Modification International, recently began seeding clouds in southern Wyoming. Now the North Dakota-based company is working with Jackson County, Colorado, on plans to boost snowfall in the lower Medicine Bow Range northwest of Fort Collins.



Snowpack from that mountain range ends up in the headwaters of the North Platte River and Walden Reservoir, northeast of Steamboat Springs. Jackson County water officials have filed permits for the project with the state Department of Natural Resources and final approval is only a matter of paperwork.



Colorado has 112 ground-based generators that work to make it snow, but the Jackson County cloud-seeding proposal is the first to use an aircraft.



Weather Modification International president Neil Brackin said he’s excited several states are more seriously considering cloud seeding as they craft drought mitigation strategies. Seeding by aircraft, he said, is far more efficient than by ground-based generators.



“It’s very clear this has great potential,” said Brackin, who estimated cloud seeding by aircraft can increase a storm’s snowfall by up to 10 or 15 percent. “There is no more doubt.”



Aircraft seeding removes the guesswork that comes with seeding from generators on the ground that rely mostly on wind to get as much of the silver iodide as possible into the clouds. Generators in Colorado are positioned at high elevation, on remote ranches and atop ski hills. Once ignited, either manually or by remote control when a storm is passing overhead, the generators vaporize silver iodide and send it skyward.



Weather Modification International has been cloud seeding by airplane since the company was formed in 1961 by a group of farmers who wanted to reduce damage from hail storms in western North Dakota.



In summer months, the company seeds clouds with silver iodide to disperse precipitation among more particles — attempting to make the clouds rain or drop tiny hail instead of balls of ice big enough to damage crops. It’s a slightly different process than what the company does to increase Wyoming winter snowpack, but it’s a similar idea.

MORE: Read more environmental coverage from The Colorado Sun.

Other states that rely on Colorado River pitch in to fund cloud seeding

In a key change this year, all seven Colorado River states signed a formal cost-sharing agreement on cloud seeding.

“It’s a historic collaboration,” said Joe Busto, coordinator of Colorado’s weather modification program at the state Department of Natural Resources. “Never before have all states pitched in together. It’s not just the money, it’s the science and the expertise.”

The collaboration is among the states that include the upper and lower basins of the Colorado River — Colorado, Wyoming, Utah, Arizona, Nevada, California and New Mexico. Each state sends a representative to sit on a weather modification advisory committee.

For years, funding from other states that depend on Colorado’s snowpack has helped Colorado upgrade its cloud-seeding operations, replacing manually operated generators with remote-controlled ones high on mountain ridges, and trading in old-school, handwritten log books for computerized data, Busto said.

The state’s weather modification program has about $520,000 in grant funds to spend on local cloud-seeding projects this winter. State grants will help buy a remote-operated cloud-seeding generator in the San Juan Mountains, as well as a device to detect atmospheric conditions from a perch atop a school in Walden.

The state also plans to kick in funds so Jackson County can do a comparison study after it begins seeding by aircraft, measuring snowfall in a stretch of forest where no cloud seeding will take place.

In Colorado, the state, local water districts, towns and ski resorts all contribute to the $1.2 million annual spending on cloud seeding, Busto said.

Among the biggest Colorado-based cloud-seeding companies is Western Weather Consultants, which operates 73 generators in the Vail area and in the San Juan Mountains.

Owner Eric Hjermstad compared the recent buzz about cloud seeding to the interest that has peaked in other periods of extreme drought, including in 2002 and in 1976, the year his father started the company. “Droughts definitely spur people on thinking outside of the box,” he said.

In a good season, which runs November through March, Western Weather typically seeds about 24 storms. Last year though, “when we didn’t have clouds in Colorado,” the company seeded just 12 storms in the San Juans, Hjermstad said.

The company has no plans to start seeding by aircraft — in part because of the expense, but also because most of the company’s cloud-seeding operations are deep in the mountains, typically at about 9,000 feet in elevation and in terrain dangerous for flying, Hjermstad said. He estimated ground-based cloud seeding costs as little as $4 per acre foot of water produced, while seeding by air is $75 per acre foot.

A cloud-seeding aircraft flies above North Dakota. Silver iodide is dropped into supercooled, liquid-filled clouds by flare. (Photo provided by Weather Modification International)

Are we stealing from Kansas?

States that rely on the Colorado River — and snowpack in Colorado’s mountains — are collaborating on cloud seeding, but an interesting question that gets to the heart of water politics occasionally arises: Could one state’s efforts to force moisture to drop from the sky rob water from the state where that precipitation might have fallen naturally?



Who can say, is the answer, at least with today’s technology. Only Mother Nature knows where that snow or rain was going to fall — maybe the middle of the ocean, or maybe it would have stayed in the atmosphere.



Another debatable question is whether cloud seeding can help Colorado and other drought-stricken states in the long term when global warming means fewer seedable storms. Seeding works best when a storm is already about to bring snow.



“The trick to weather modification is that you have to have seedable events,” said Bruce Whitehead, executive director of the Southwestern Water Conservation District. “You still have to rely on Mother Nature.”



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