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Cloud seeding enters second year of data collection

by Wyoming Livestock Roundup

The 2007-2008 cloud seeding season has already contained several seeding events, according to Cloud Seeding Project Manager Barry Lawrence.

“All the permitting is complete that was necessary to get the generators in, so we’ve got more operating this year, with 24 in all,” he says. In addition to the added generators, he says overall conditions have been favorable for seeding.

Eight generators have been placed on the western flanks of each of three mountain ranges: the Sierra Madres, the Medicine Bows and the Wind Rivers. Crews are based in Rock Springs and Saratoga, with aircraft also based in Rock Springs.

“We’re doing weather balloon launches when necessary, which is one or two times per day, depending on the weather fronts that are moving through,” explains Lawrence. “We’ve also got high-resolution precipitation gauges deployed in both target and control areas.”

In addition to the data collection that directly relates to the cloud seeding, Lawrence says the project presents unique opportunities for other scientists’ research, including projects such as snow sampling and Wyoming cloud radar.

“We have radiometers deployed that look like overgrown mailboxes. They look for super-cooled liquid water coming off the mountain ranges and help determine if conditions are right for a seeding event. The Desert Research Institute out of Nevada is doing snow chemistry sampling and we’re also working with the Center for Atmospheric Research in refining the experimental design in our equipment, since this is still a pilot project,” he explains. The University of Wyoming is also very involved in the monitoring of cloud seeding.

Because the cloud seeding is a five-year pilot project with the goal of building up a number of cases for research, randomized seeding events are conducted in the Medicine Bows and the Sierra Madres. “The meteorologists look at the conditions and decide to call a case and they indicate which generators should be used and pass that information on to a technician, which receives a seeding decision,” explains Lawrance. A seeding case is only called if conditions are similar on both mountain ranges.

If the decision to seed is made, the generators are turned on remotely and run for four hours. “We don’t want to bias the scientists for calling the next case, and we don’t want the meteorologists to know which range was seeded. They try to see the signature for themselves through snow chemistry sampling, precipitation gauges, etc.,” he says.

The research strategy is called a “crossover” design. By running both mountain ranges at once, the project doesn’t have to have hundreds and hundreds of cases. “It reduces the number of cases we need to have to see a signature,” says Lawrence.

The Wind River Range is on more of an operational basis, but is still being evaluated through snow chemistry sampling and precipitation gauges.

As with the 2006-2007 season, this winter’s seeding season will run through early spring, whereupon the researchers will wait again until the next winter to begin running tests again.

Christy Hemken is assistant and crop editor of the Wyoming Livestock Roundup. Send comments on this article to

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