- Associated Press - Thursday, May 1, 2014

CHEYENNE, Wyo. (AP) - Scientists are encouraged by preliminary research that shows seeding clouds enhanced the amount of snow in winter storms over mountain ranges in southern Wyoming but say more study is needed to determine if the practice results in increased snowfall or rainfall on the ground.

“There does seem to be some evidence for seeding to impact the cloud,” Bart Geerts, a University of Wyoming professor of atmospheric science, said.

The research led by Geerts was done in conjunction with a larger, nearly decade long, $13 million project by the state of Wyoming to see if cloud seeding can increase snowfall in several mountain ranges.

Cloud seeding involves injecting silver iodide into clouds either from aircraft or from generators on the ground. Under the right conditions, the chemical can help water droplets grow onto snow and fall to the ground. The practice is used in a number of states and in other countries in hopes of increasing precipitation for agriculture and municipal water supplies, but it is still uncertain whether it really works.

The research by Geerts was funded by the National Science Foundation and, using sophisticated ground and airborne radar and computer technology, looked at whether ground-based cloud seeding generators physically increased snow inside clouds. The field research was conducted in 2012 and 2013.

“The overwhelming evidence from three different radars and also from instruments on the ground is that there is some impact when the seeding plume comes overhead,” he said. “We get on the order 25 percent increase in precipitation during those cases that we selected. This is an average based on all 26 cases and all three radar systems.”

His research did not seek to determine whether more snow accumulated on the ground as a result of cloud seeding.

“We looked more at physical processes from the moment the seed material is dispersed from those generators to the time the snowfall reaches the ground,” Geerts said.

Several peer reviewed papers of the research led by Geerts have been published and several more are in the works. In addition, the research will be included in the final report that will be issued later this year by the larger cloud-seeding project, which does seek to determine whether the practice increased snowfall on the ground in the mountain ranges.

Chungu Lu, a program director with the National Science Foundation’s atmospheric and geospace sciences division, said the results from the research by Geerts is “pretty promising and encouraging.”

Lu cautioned that cloud-seeding research is extremely complicated, noting that the Wyoming research is the first the foundation has funded in decades. The foundation provided $1 million for the research led by Geerts.

“Science and technology have advanced … enough to really look at this old problem, and that’s why we funded this project,” Lu said.

He said the Wyoming results should encourage further cloud-seeding research, particularly into the airborne-based seeding generators that are more commonly used.

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