The science behind cloud-seeding

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SHERIDAN— As a year-long study gets underway to assess the feasibility of cloud-seeding in the Bighorn Mountains, we thought we’d dig in on the science behind what many think of as man-made clouds.

What is cloud-seeding?

Cloud-seeding is just what you might think: planting “seeds” that will help clouds grow in the atmosphere, producing more precipitation. In this case, those seeds are any agent that causes water to freeze at a warmer temperature than it otherwise would. Dry ice particles and silver iodide are two of the most common agents used.

Is this new?

The process has been in use since the 1940s, when Bernard Vonnegut, the late brother of the novelist Kurt Vonnegut, Jr., began experimenting alongside colleagues in the General Electric Research Laboratory in Schenectady, New York, where he worked.

Is it new to Wyoming?

No. Wyoming conducted a $13 million study on cloud-seeding that spanned 2005-2014.

How does it work?

Cloud-seeding can be done from the ground, using a generator that emits the ice-forming agent into the air, or it can be done by plane.

Whether it’s silver iodide (which is also used to develop photography film), dry ice or some other agent, the material released into the storm system acts as a solid structure around which the water in the atmosphere can form and freeze.

Bruce Boe, vice president of meteorology at Weather Modification, Inc., is helping to conduct the feasibility study in the Bighorns. Boe said that water does not “know” how to rearrange its liquid molecules into a solid form on its own in the atmosphere, even when the temperature gets below 32 degrees Fahrenheit, which is the freezing point on the ground. This is called “supercooled” water.

Boe said that without cloud-seeding agents, water can freeze in the atmosphere at around -4 degrees Fahrenheit or colder.  The cloud-seeding agents allow that to happen at 21 degrees Fahrenheit or below.

What are the benefits?

Cloud-seeding leads to increased rain and snow. While it is difficult to measure the increase in precipitation that results directly from cloud-seeding efforts, due to the many factors in a storm system, a rough, general estimate is that cloud-seeding will increase precipitation by five to 15 percent, Boe said.

What are the drawbacks?

The Weather Modification Association argues that cloud-seeding is safe for the environment and human health.

“Measurements made since the 1950’s indicate that the amount of silver iodide deposited in a target area after a long standing cloud seeding project falls several orders of magnitude (multiples of 10) short of the amount known to be toxic to plants, animals, trees, or humans,” reads a statement on the group’s website.

Representatives from the Wyoming Department of Environmental Quality and Sheridan County Public Health both said their offices were not aware of negative environmental or human health impacts from cloud-seeding.

Another concern some have is that cloud-seeding could spur litigation based on beliefs that altering natural precipitation patterns in some areas could lead to droughts or floods in other nearby areas.

For example, in 1974 the Montana Wilderness Association filed a lawsuit against a hydroelectric power company pursuing cloud-seeding projects. The MWA argued that cloud-seeding would alter or harm the natural area. The power company cancelled its cloud-seeding plans before the court could rule on the issue.

In North Dakota in 1981, plaintiffs argued that Weather Modification Inc., the company assisting with this year’s study in the Bighorns, caused a downpour that lead to flooding and damage of the plaintiff’s property. Procedural issues prevented the courts hearing this case from ruling on the plaintiff’s claims.

Why the Bighorns?

While the study is not yet complete, Boe said that the Bighorns could be a productive location for cloud-seeding. The mountain range is situated perpendicularly to winds coming in from the southwest and it is long enough that storms cannot easily pass around it. High peaks in the Bighorns also help to create more precipitation.

By |Nov. 7, 2015|

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