Wind farms stir up trouble

SIOUX FALLS, S.D. | Wind farms have been blamed for disrupting the lives of birds, bats and, most recently, the land-bound sage grouse.

Now the weatherman?

The massive spinning blades affixed to towers 200 feet high can appear on Doppler radar like a violent storm or even a tornado.

The phenomenon has affected several National Weather Service radar sites in different parts of the country, even leading to a false tornado alert near Dodge City, Kan., in the heart of Tornado Alley. In Des Moines, Iowa, the weather service received a frantic warning from an emergency worker who had access to Doppler radar images.

The alert was quickly called off in Kansas, and meteorologists calmed down the emergency worker, but with a major push toward alternative energy and enough wind turbines going up last year to power more than 6 million homes, more false alerts seem inevitable.

New installations are concentrated, understandably, in windy states, including Texas, Oklahoma, Kansas, Colorado and Iowa, all part of Tornado Alley.

Texas, which has more tornadoes than any other state, has the most wind-power capacity.

Dave Zaff, science and operations officer with the National Weather Service office in Buffalo, N.Y., describes the wind farms 20 to 35 miles to the southeast as “more of a pimple or a blotch on your face” that 99 percent of the time will not pose a problem.

But what about those busy, high-stress periods when a meteorologist is tasked with making quick decisions as storms grow violent? In a worst-case scenario, a forecaster could disregard a real storm for turbine interference but more likely would err on the side of caution, Mr. Zaff said.

“If you take a glance and then all of the sudden you see red, you might issue an incorrect warning as a result,” he said.

Problems began to surface about three years ago and seem to occur where a wind farm is built within about 11 miles of a Doppler site, said Tim Crum of the weather service’s Radar Operations Center in Norman, Okla.

That could become a bigger problem because the same terrain is attractive for both weather radar and wind farms.

“They want to be out in relatively exposed areas, high terrain, those sorts of things,” Mr. Crum said. “So we sometimes are looking for the same ground, although we’re already there.”

Software can easily filter out buildings, cell towers and mountain ridges on radar screens. Yet because weather radar seeks motion to warn of storms, there’s no way to filter out the spinning blades.

Microwave radio signals are beamed toward a particular point, and meteorologists listen for the “reflection.” Experts can pick out the shape of a storm or a tornado.

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