A dozen weather-modification professionals from as far away as North Dakota and Arizona observed Medford's contribution to their science Thursday morning.

Airport staff demonstrated the cloud-seeding CASPER system, used to clear fog above the runway, for the North American Weather Modification Council members in town for a biannual conference.

The Cable Attached System Providing Effective Relief, which was designed to clear fog in below-freezing conditions, was introduced in 2010. An 18-foot, helium-filled balloon hoists a 75-pound dispersal cylinder 500 feet above the runway, where it spews ice pellets for 30 minutes.

Last winter it was needed only three times, Robert Russell, airport operations director, told the visitors. But two years ago, CASPER was called out 20 times.

Weather-modification scientists generally seek broader solutions to increase summer rain and winter snow, said Tom Ryan of the Metropolitan Water District of Southern California.

"This was a whole new application of weather modification. We came to see if there is anything we could learn," Ryan said.

He was impressed at the rapid turnaround time for the system.

"The processes we follow take a lot longer period of time to become active, and this is instant," Ryan said. "That's the most fascinating thing, how quickly it works. In our work, it's hard to see results. For example, if we're trying to make snow in a mountain range, it's 20 miles away. We will only know once we do additional testing that it worked. Two, three months later, we collect the data and do the work. Here you see instant results."

NAWMC members often work in arid regions, and they gather twice a year to discuss their projects. Earlier this year they met in Long Beach, California, and next spring they will be in Boise, Idaho.

The council's members are a mix of weather-modification scientists and program participants, said Mohammed Mahmoud, of the Central Arizona Project, who earned his doctorate in hydrology and water resources at the University of Arizona.

"From Central Arizona Project point of view, we like to fund weather-modification activities in the upper basin of the Colorado River," Mahmoud said. "The idea is that if we increase winter precipitation, increase the snow, we increase the snowpack and therefore when runoff season occurs in the spring, it boosts some of the flows of the Colorado River, and that helps us all the way downstream in Arizona, because it increases the amount of storage in Lake Powell and Lake Mead, and the health of Lake Mead is directly related to how much water we can receive."

Maury Roos, chief hydrologist at the California Hydrology & Flood Operations Office, likened CASPER to similar approaches by the Air Force in Alaska.

"This is a different application for fog clearing," Roos said.

There are a dozen mountain watershed projects in California, following the principles used in producing snow for a ski area — but at a much greater scale, he said.

"Most of the work we do is to increase water supply by increasing the amount of natural rain and snow that falls in suitable storms," Roos said.

Other airports use other methods, Russell told council members. In Missoula, Montana, liquid carbon dioxide is used to clear fog, while propane is used in North Dakota.

"This is really about learning," Ryan said. "Nothing moves quickly in our field, because the science slowly moves along. This is one more input that we'll take back and think about."

 — Reach reporter Greg Stiles at 541-776-4463 or business@mailtribune.com. Follow him on Twitter at www.twitter.com/GregMTBusiness, on Facebook at www.facebook.com/greg.stiles.31.