Commanding the Clouds: Telski Expands Experimental Cloud Seeding Program


The new remote cloud seeding generator is located on Hastings Mesa to target Telluride. (Photo by Alec Jacobson)

By Alec Jacobson | Telluride

El Nino laid down a strong snow base in Telluride in January, but, says Jeff Proteau, Telluride Ski & Golf’s Vice President of Operations, “Don’t be fooled, our snow is low this year.”

Fortunately, Mother Nature may have had a little help from a new cloud seeding generator up on Hastings Mesa.

At the beginning of 2016, Larry Hjermstad’s Western Weather Consultants flipped on the generator – the newest in its network – to target the slopes of Telluride. Hjermstad has run similar generators since the late ‘70s, though the new machine is only the second remotely operated cloud seeder in the Western San Juan chain. The other machines in the region are positioned within close range of homes so that they can be flipped on manually at any time of the day or night.

The remote generator, developed by and bought from the Desert Research Institute, can instead be positioned more optimally for cloud seeding efficacy.

“We’re trying to do this on a reasonably narrow focus,” said Hjermstad. Though he has not made formal projections, he believes that 50-70% of storms passing over the new generator will be seed-able. Storms moving in similar patterns in the region tend to react well to seeding, he said, dropping an extra 14-15% precipitation when seeded to increase season moisture totals by 8-10%.

The location was chosen based on wind data indicating that precipitation in Telluride tends to spin around through the box canyon, coming from down valley rather than  plowing straight over from Mt. Wilson.

So far, the Hasting’s Mesa generator has been turned on during seven different storms this year, for a total of 51.95 hours. There is no measure of its current success rate.

Telluride Ski & Golf has, on and off, paid to support regional cloud seeding since 1977, helping to ensure the operation of 12 of Hjermstad’s generators that might hit the ski area. TSG currently pays $15,100 per year, contributing toward the total project budget of $71,260.  TSG and the Colorado Water Conservation Board split the cost of the new $34,000 generator.

Particularly compared to the “seven figure” snow making budget, “it’s not a huge cost liability,” Jeff Proteau says, though, “I don’t know how long I’ll be advocating for it.”

“Do we count on it for our snowpack, no, we count on Mother Nature for our snowpack, but, if we can enhance the snowpack, we can provide ourselves with a little insurance,” says Proteau, “We look at the mountain here as a reservoir for downstream use.”

But not everyone is optimistic about regional cloud seeding efforts. “The county looked at this and decided that the science did not seem strong enough to spend tax payer money,” said San Miguel County Commissioner Art Goodtimes.

A Summary of Current Programs and Opportunities for Enhancements

A Summary of Current Programs and Opportunities for Enhancements (Courtesy Image)


Controlling the weather as a tool for agriculture or a weapon in war has long been a dream, with all manner of shams and shamans working to command the clouds throughout history.

Early rain dances, sacrifices and superstitions gave way to pseudoscience in the 1800s. James Pollard Epsy theorized that hot air would rise and then cool, causing condensation and petitioned Congress to burn large swaths of land in a north-south line linking America’s borders to produce clouds though this process. Others devised a mile-high berm across the plains to lift the winds until they cooled into rain. Through the early 20th century, many sold their services as small-scale rainmakers, throwing different chemicals into the sky.

A U.S. Bureau of Reclamation report by Jedediah Rogers noted in 2009, “It might appear perplexing in hindsight why people would pay well for services of questionable validity, but water users facing shortage and a failed crop might have seen rainmaking as a legitimate risk to take. Moreover, although no one could prove the validity of rainmaking, neither could they disprove it.”

It wasn’t until the mid-1950s that scientists began to establish methodologies that could withstand some scrutiny. Irving Langmuir, Vincent Schaefer and Bernard Vonnegut, working at General Electric Laboratories, stumbled upon the realization that clouds could be artificially supercooled to induce some precipitation, when Schaefer noticed the phenomenon on a small scale caused in his ice box. The team tested the theory by depositing dry ice into clouds in 1946. Vonnegut noticed that silver iodide could be used to similar effect.

The results were promising, though not conclusive. And the researchers were far from confident about the weather conditions necessary for success. But scientists, politicians, farmers and salesmen quickly latched onto the belief that full control of weather was within human grasp.

The U.S. Bureau of Reclamation, tasked with harnessing the West’s water resources, started building on that research in 1947, hoping to complement its many damming projects. At the same time, private cloud-seeding firms sprang up across the country, promising extraordinary results and reaping millions of dollars in return.

In 1951, Congress passed a bill to assess the data on weather modification and, in 1953, formed the Advisory Committee on Weather Control. On the one hand, proof and improvement of cloud seeding technology required the coordinated analysis of massive amounts of data. On the other, the government sought to protect consumers from what appeared to be rampantly fraudulent weather control providers.

In 1961, Congress approved $100,000 to finance cloud-seeding research, initiating Project Skywater under the Bureau of Reclamation to focus on augmenting the nation’s water supply. Led by a team of researchers at the Engineering Research Center in Denver, many of the project’s studies focused on the Colorado River Basin.

By the late ‘60s Skywater had generated some positive results, but also opened many more questions and little hard evidence of success. Never well-funded, the project’s budget was slashed during the Vietnam War as scientists’ hopeful boasts of “driving tornadoes” within two generations were downgraded to more realistic predictions of small gains in precipitation after many more tests.

State and federally funded research continued through the 1980s, increasing confidence in cloud seeding and improving understanding of the optimal meteorological conditions for operations to have the best chances for success. But the government did not move beyond research into operation, lacking both confidence in Project Skywater’s results, and the stomach to continue on with such uncertainty.

Private weather modification companies however stayed the course, working to apply the government’s research to build the best equipment and most precise techniques.  For some farmers, ski areas and even some foreign governments, it was worth paying to apply the generally positive research if it had even a chance of improving their water supply.

“There’s always been a desire to find a cheap silver bullet and, in this case, it’s silver iodide, though it’s not that cheap,” says Colorado’s State Climatologist Nolan Doesken.

The government of the People’s Republic of China, by comparison, has invested heavily in weather modification, employing some 37,000 people and spending $63 million per year to garner what it reports as $1.7 billion in benefits according to the New York Times – including an effort to ensure optimal weather for the Olympic Opening Ceremony in 2008.


Telluride Target Map (Courtesy Image)


Since the end of government-backed studies in the Upper Colorado River Basin, Colorado has been a hub of commercial cloud seeding activity. As of 2014, there were 107 active generators in Colorado used by seven permitted programs targeting the Central Colorado Mountains River Basin, Vail/Beaver Creek, the Upper Gunnison River Basin, the Western San Juan Mountains, Eastern San Juan Mountains, West Dolores and Telluride Ski Resort Area.

Each program is funded through a mix of local water boards, private interests, the Colorado Water Conservation Board and the Lower Colorado River Basin States. Since 2009, the total annual spend on cloud seeding in Colorado has been stable at $1 million per year, with 65% of funding from local sources, 18% from the Colorado Water Conservation Board and 17% from the Lower Basin States.

These active programs are not scientific studies and, as such, do not carefully track outcomes. Every winter is different and such projections and calculations are difficult to make with any degree of accuracy.

According to Joe Busto, Weather Modification & South Platte River Program Coordinator at the Colorado Water Conservation Board, “As far as quantifying the water, we typically stay away from that and hide behind well-designed and executed programs [that] have demonstrable results as stated in the policy statements. It’s even written into our agreements to stay away from spending too much money or time going down that rabbit hole.”

“The joke I have is I am just on the mop up crew cleaning up old programs and making them new,” says Busto, “[doing] what they told us to do that no one ever did.”

The Vail/Beaver Creek Program was Colorado’s first cloud-seeding program, operating continuously since 1977.

Interest from the Lower Colorado Basin States has been consistent throughout the history of cloud seeding. Water from the Rockies feeds Lake Powell and Lake Mead, quenching thirst throughout the parched West. As water shortages persist, California, Nevada, Arizona and New Mexico are looking to fill their water gap in any way possible. Relative to pulling water from the ocean at a cost of as much as $2,000-3,000 per acre foot, cloud seeding is estimated to cost far less – closer to $5-500 per acre foot.

One key challenge in the cloud seeding debate is ownership of the generated water. International conversations on the ownership of clouds have suggested that water vapor be treated like fish in the sea – without owners until it is harvested – but there have yet to be significant tests of such policy.

In Colorado, the question of ownership has so far been side-stepped altogether. Busto, for example, avoids quantifying the effects of different programs because, in a water landscape already fraught with intertwined treaties, “We don’t want to be in a place where a number of additional water generated is a poker chip to let water out of a dam or something like that,” he said.


Even as cloud seeding experts have risen above the level of snake oil salesmen, the technology has been difficult to prove absolutely.

“It’s like God,” said Busto. “You either believe or you don’t.”

According to a 2005 paper sponsored by the Colorado Water Conservation Board, there are three main angles in the cloud seeding debate: those who feel that the technology has not yet been thoroughly proven, those who feel that it is efficacious and worthy of widespread use, and a camp that “sees application as a sensible bet when uncertainties and large potential gains are weighted against the relatively low cost of application.”

“Weather is so naturally variable,” said Nolan Doesken, Colorado’s State Climatologist – and there are no perfectly accurate forecasts. For the same reason, he added, there are relatively few studies that have the statistical rigor to prove cloud seeding is effective.

Cloud seeding is based on natural inefficiencies in the sky. There is no weather modification program that can produce new clouds. Rather, operators target existing clouds within a narrow range of conditions that might be exploitable.

Storms disperse only a small fraction of the total water that they carry. For precipitation to occur, water vapor must be super-cooled to form ice nuclei around which other water molecules can condense and fall. Weather modifiers seek to increase precipitation by seeding clouds with artificial nuclei. Silver iodide and propane can both be dispersed into clouds, either by burning them in a ground-based generator or by depositing them from a plane. Both molecules are geometrically similar to natural ice crystals and so are effective at catalyzing condensation.

In mountainous terrain, studies have shown ground-based generators to be preferable to plane dispersal. Generators are placed upwind of a target area on the windward side of a peak in order to propel the plume of seeds into position in nearby clouds.

Not all clouds are seed-able, so generators are only turned on when conditions seem appropriate. Currently, radiometers that can measure the conditions within individual clouds accurately are being tested for use in cloud seeding. Potentially, the ability to narrow the window of efficacy from an entire storm’s worth of clouds to a few specific patches could save money and increase efficiency.

In winter storms, temperature and ice nuclei ratios produce snow around -15 Celsius. Cloud seeding generators provide nuclei at higher temperatures than they would normally occur – up to 0 Celsius using propane or -8 C with silver iodide – and add extra nuclei where they occur naturally. The result is that a seeded storm should start to precipitate sooner and ultimately deposit more water than it would naturally.

Models suggest that seeded storms should generate 5-15% more precipitation, but large-scale experiments have not necessarily confirmed this.

Models suggest that seeded storms should generate 5-15% more precipitation, but large-scale experiments have not necessarily confirmed this.

An a posteriori independent analysis of the long term data from Vail’s cloud seeding program from 1977-2005 yielded some statistically significant results, including measurements that show as much as a 45% increase in snow water equivalent at one site.

However, this analysis concludes, “The results of the evaluations in this study must be viewed with caution…From a rigorous statistical standpoint, the suggested effects that are indicated must be confirmed through new, a priori, experiments specifically designed to establish their validity.”

The Vail program was conducted by Larry Hjermstad not as a rigorous, scientific study but rather as an operation to increase snow. As a result, like any early studies in cloud seeding, the data did not include any randomization or control group, making it impossible to determine whether or not seeding was effective or if positive results were achieved by pure chance.

Beginning in 2004, the Wyoming government funded the Wyoming Weather Modification Pilot Program – the first government-funded study since the end of Project Skywater – to provide more scientifically significant results. The study monitored precipitation in two mountain ranges, seeding one with silver iodide at randomized intervals and leaving the other as a control.

Unfortunately, it was discovered mid-study that the control range was actually within the potential spread of the seeding project. Eliminating much of the data to compensate for that failure, analyses suggest that the program produced 1-3% more water for the seeded region during the study. The confidence rating in that result was 72%, meaning that there was a 28% chance the result happened by chance.

The program’s own executive summary from 2014 raises doubt about the program’s efficacy, stating that “since the p-value [that the result was achieved by chance] is greater than 0.05, the primary statistical analysis indicated no significant seeding effect.” (Statistical proof typically requires a greater than 95% assessment that the result was achieved through the tested method rather than randomly.)

Nevertheless, the results were good enough for the Wyoming legislature, which approved a $1.4 million cloud seeding program in April 2015 based on the test results.

Scientists from across the West also deemed the program to be a success. “If you look at enough data for long enough, it’s pretty clear that it’s good,” said Frank Mcdonough, Atmospheric Scientist and Program Manager at the Desert Research Institute in Nevada.

“I’m relatively convinced that their study is robust,” agreed Colorado climatologist Doesken. “At a .72, in climate science, that’s not too bad. That’s probably actionable.”


Alongside the early assumption that humans could control the weather was the concern that cloud seeding experiments might inadvertently cause massive increases in precipitation. In one famous incident in 1916, career rainmaker Charles Hatfield’s powders and potions purportedly produced enough rain to flood San Diego and wash out dams.There was no proof of causation, but the story and others like it have resonated throughout the modern history of weather modification.

A 2009 report by the U.S. Bureau of Reclamation noted that one Telluride-area miner in the ‘70s was so concerned that tests in the region might produce excess snow, avalanches and mudslides that he threatened, “If those weathermen screw up life around here they may suddenly discover their equipment blown to bits.”

Colorado still mandates that weather modification programs be shut down if snowpack snow water equivalent (the depth of the snowpack converted into actual water content) jumps above 175% by Dec. 1 or above 140% by April 1 in any year. This has happened periodically, though there is no evidence to suggest that cloud seeding was to blame for the above average results.

On the other side of the spectrum, some Colorado residents – particularly those in the Eastern Plains – worry that cloud seeding in the mountains might deprive them of water. Doesken says that such a “wind shadow effect” is possible but unlikely, and currently below measurable ranges, given the limited efficacy of cloud seeding.

Assuming that cloud seeding increases precipitation by 10%, it affects less than 1% of the total water vapor in a storm, according to a 2015 report prepared for the Colorado Water Conservation Board.

“If we get to the time where we’re seeding every mountain range, you can’t say that with as much confidence,” Doesken said, explaining that seeding would need to become significantly more efficient and widespread before its effect downwind reaches a level that could be detected.

Doesken added that the plains receive little of their annual precipitation during the winter, relying more heavily on summer storms. Beyond that, he explained, Front Range storms typically don’t pass over Colorado’s mountains, swelling instead from the south or northwest, whereas the Western Slope’s precipitation typically comes from the Pacific.

These weather patterns suggest that even if there was some wind shadow effect from cloud seeding on the Western Slope, it would not affect the winter precipitation on the Front Range.

“It’s not like we’ve decided this is the best thing since sliced bread. It’s a grand science experiment and we need to continue to study it.”Colorado Water Conservation Board member April Montgomery.

The potential toxicity of silver iodide is an easier threat to assess. Australian scientists Bruce Williams and John Denholm published a paper in 2009 in the Journal of Weather modification concluding that cloud seeding poses no silver iodide poisoning risk.

Ionized silver, Ag+, is known to be fungicidal and bactericidal. It is harmless to humans until it reaches an incredibly high dose and, up to that point, is used to purify water and also in those fancy stink-killing shirts. Lower concentrations have been observed to cause defects in some continuously exposed fish eggs. However, Ag+ is naturally occurring. Even taking into account the additional silver from cloud seeding, the measured levels are, according to Williams and Denholm, “several orders of magnitude below the chronic toxicity level.”

The quantity of silver iodide distributed in a cloud seeding program is relatively small and used over a large area. For instance, the Telluride generator burns between 5 and 15 grams of silver iodide per hour and has distributed a potential maximum of 584.25g of silver iodide over hundreds of square miles during its 50-plus hours of operation so far this winter.

Experts contend that beyond the small amount of material burned in generators, cloud seeding’s addition to the baseline of environmental Ag+ is small because silver iodide, AgI, is insoluble in water. Thus, according to Williams and Denholm, it tends to yield a miniscule quantity of the silver ion, Ag+, naturally. That’s part of the reason that AgI is effective in cloud seeding, tending not to fall apart before it can act as an ice nucleus.

“Available scientific research has clearly documented that winter cloud seeding with AgI has no adverse environmental effects,” notes a 2015 Water Conservation Board packet. But the absence of current evidence of harm has stopped neither critics nor proponents of cloud seeding from continuously double checking.

“I get asked quite a bit, ‘Aren’t you fooling with Mother Nature?’ We do forest management. I look at this as water management,” said April Montgomery, member of the Colorado Water Conservation Board. “It’s not like we’ve decided this is the best thing since sliced bread. It’s a grand science experiment and we need to continue to study it.”


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About the Author

Alec Jacobson

Alec Jacobson has worked as a photographer around the world and was recently selected as a National Geographic Young Explorer. Before moving to Telluride, he was the Editor in Chief of, building the site from a blog into an online culture magazine. He graduated from Amherst College in 2012, where he studied Anthropology, French and Arabic.