Lack of clouds - and interest - cited as key barriers to its practice.
Even the rainmakers say they can't end Minnesota's drought.
"The reason we're in drought is because we don't have any rain clouds. We can't make clouds," said Hans Ahlness, vice president of operations for Weather Modification Inc., a cloud-seeding firm in Fargo.
Several of Minnesota's neighbors have tried weather modification over the years, but Ahlness said no one from the state has inquired about it during the current drought, which has been deepening across the state, particularly in the southwest and northwest corners.
In fact, cloud-seeding seems to have generated more indifference than rain in Minnesota, despite some historic dry spells.
The state's 1976 drought prompted community fund drives in western Minnesota to pay for cloud-seeding and, according to a legislative report, fears of "unethical cloud seeders." It also led the Legislature to pass a measure in 1977 regulating the practice. But by 1999, even through the drought months of 1988, no one had ever applied for a license, and the regulations were repealed. The period since then, despite some dry periods, has seen average annual precipitation increase across the state.
Cloud seeding involves blasting particles, usually silver iodide, into a cloud, where they attract water vapor, ultimately forming drops heavy enough to fall as rain. In conditions that could produce hail, the particles act as nuclei. Increasing their number in a cloud can produce many small hailstones instead of relatively fewer big ones, minimizing the risk of heavy damage on the ground.
The effectiveness is difficult to prove, since no one really can determine how much precipitation would have fallen without the seeding.
North Dakota has conducted a cloud-seeding program in six western counties for more than 50 years, using Ahlness' firm. Studies by North Dakota State University have shown that seeding increases rainfall 5 percent to 10 percent per year, while reducing hail damage by 45 percent. Those changes have allowed growers to earn $12 million to $20 million annually from increased crop production or avoided hail losses, or both, said Darin Langerud, director of the North Dakota Atmospheric Resource Board.
In Alberta, insurance companies endorsed cloud seeding in 1996, when 112 of them formed the Alberta Severe Weather Management Society. It continues to contract with Ahlness' company for hail suppression in the Calgary area.
South Dakota began cloud seeding in 1971. But the program was stopped after being blamed both for the massive flash flood that killed 238 people in Rapid City in 1972, and for drought three years later, according to South Dakota School of Mines and Technology professor emeritus Paul Smith.
Weather modification has been a subject of experimentation -- and science fiction -- since the 1940s. It's widely used in China, where it was credited with diverting rain from the opening ceremonies of the 2008 Olympics. It's used in the western United States to create snow and water for irrigation and hydropower. The U.S. military used it in Vietnam to make travel along the Ho Chi Minh trail difficult for the North Vietnamese and, in 1977, the United Nations moved to prohibit its use in warfare.
In Minnesota's recent drought, the raw materials for rainmaking -- clouds 8,000 to 10,000 feet deep, a mile wide and with tops up to 30,000 feet-- have been rare. And in any case, it's unlikely the rain they might produce would alleviate the widespread dry conditions.
"Weather modification is a really rotten drought mitigation tool," Ahlness said.
Bill McAuliffe • 612-673-7646