major cloud seeding test gives mixed results

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Remember those reports of people burning snow from last year? [You must be registered and logged in to see this link.]

Quote :: For the past six winters, meteorologists have sprayed silver iodide particles into storm clouds rolling over Wyoming’s mountains to see whether the technique can increase snowfall.

The experiment was one of the longest-running and most rigorous tests yet of ‘cloud seeding’. An independent team of scientists now says that it worked — sort of.
Seeding the clouds squeezed 5–15% more precipitation out of them, says Roy Rasmussen, a meteorologist at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, who led the evaluation team. But that statistic holds only if scientists eliminate parts of the test that went wrong, such as when the silver iodide spray did not completely cover the mountain range that the researchers were trying to seed.

Quote :: Over the course of six years, the team ended up with 118 cases of cloud seeding in one range or the other. Analysis of those alone was not enough to suggest that cloud seeding increased precipitation, Rasmussen says.
But then the team decided to drop some cases out of their data set. They eliminated the couple of times when silver iodide from the seeded mountain range had drifted as far as the unseeded control range, contaminating it. And they eliminated many cases where not all generators were turned on in the seeded range — for instance, because the winds were blowing in a direction that could have dumped extra snow on an important interstate highway.