Could a Long Island Offshore Windfarm Disrupt Weather Radars?

Above, A marks the spot of a wind farm in central Wisconsin that is disrupting weather radars, making forecasting all the more challenging. Image source: Google Maps.

Saw a great article in the Milwaukee Journal Sentinel recently about a large wind farm disrupting weather radar capabilities in central Wisconsin. We’ve talked a lot about the benefits of wind power, especially in rural areas, to generating clean electricity. Here is a demonstrated negative consequence of large wind farm installations.

The National Weather Service has issued a new kind of warning because of a Dodge County wind farm that is disrupting the agency's ability to monitor storms in southeastern Wisconsin.

The wind farm's giant turbines - each as wide as a football field and as tall as a 20-story building - are sending false storm signals to the government's weather radar system.

Weather service officials say they see no significant public safety threat, although they say the wind farm has caused radar interference and could confuse some storm watchers.

Meteorologist Marc Kavinsky said the approaching summer storm season will be the federal agency's first opportunity to gauge the wind farm's full impact.
"It'll be interesting," he said. "I'm hoping the effects will be minimal."
Located just outside the Dodge County community of Iron Ridge, the wind farm includes 36 turbines that began operating over the past few months, generating electricity for several surrounding communities.

The farm is about 30 miles north of the National Weather Service office in Sullivan, which provides radar coverage and severe weather alerts across a 125-mile radius that includes all of southeastern Wisconsin.

The meteorologist, Marc Kavinsky, who was quoted in the article has a great website demonstrating the effects of these tremendous blades on Doppler radar returns.

His key implications of the wind farms on radar returns were:

• Thunderstorm or winter storm characteristics could be masked or misinterpreted, reducing warning effectiveness in the vicinity of the wind farm.

• False signatures contaminating Doppler velocity data in the vicinity of the wind energy facility could reduce forecaster's situational awareness, particularly
during hazardous/severe weather events.

• False precipitation estimates could negatively impact flash-flood warning effectiveness.

To summarize the above, the false returns negatively affect the weather services’ ability to forecast for severe events, like thunderstorms, tornadoes and flooding rains. While this would be a major concern in the Midwest where severe weather associated with thunderstorms is common, how important would it be here in the New York region? Let’s try to anticipate the effects of a wind farm 10 miles off of the south coast of Long Island, as has previously been proposed.


The figure above shows how topography coupled with an extremely high wind farm affects weather radards. Source: National Weather Service.

The figure above shows why the wind farm in Wisconsin is so effective in disrupting the radar signals. The radar beam is tilted up, generally in the neighborhood of 0.5 to 3.5 degrees, and in this case the beam intersects the windfarm because the terrain is sloping upward along the beam path. If the ground was flat, the windfarm would go undetected by radar. How would this work in the New York region?

The NWS Doppler radar that serves the New York region is sited on Brookhaven National Lab on Long Island. A conservative estimate of the height of the Doppler radar is 250 feet above mean sea level. Using Google earth software I calculated the distance from the radar to Fire Island on the south shore of Long Island to be about 8.6 miles. Plan for the windfarm had it to be placed about 12 miles off shore, so let’s estimate the closest possible distance between windfarms and the Doppler radar to be 20 miles (even though in the planning stage the windfarm was located futher west, increasing the distance between radar and windfarm). Next step, figure out the height of the proposed windfarm. Taking the extreme of a 20 story windfarm at 15 feet a story, we come up with a height of 300 feet. With the lowest angle (0.5) of the radar, 20 miles away the beam would be about 528’ above where it started and with the highest angle (3.5) it would be 3696’ above the ground where it started. If you ignore radar beam broadening and throw in a ground elevation of somewhere near 250’ the beam would be 775’ to 4000’ above sea level by the time it reached the windfarm.

Bottom line, a wind farm 20 miles away from the Doppler Radar would require a height of at least 775’ to interfere with Doppler radars offshore in the New York region. While wind farm interference is a problem given the complicated topography of central Wisconsin, it will likely be not be an issue with an offshore farm in the New York region.