Meteorology News

Wind turbines along the Buffalo Ridge in rural southwest Minnesota (2004)

A relatively new wind energy farm in central Wisconsin has created a newly-discovered, puzzling side effect:  interference with the local National Weather Service doppler radar.

The Butler Ridge wind farm was constructed in February of this year and contains a total of 36 wind turbines, each standing about 300 feet above ground level.  These windmills were build on a ridge line that is about 1100 feet above sea level, placing the turbines in an optimal location to benefit from the highest wind speeds in the region.  Coincidentally, the location is in the sight of the local doppler radar tower in Sullivan, WI that is approximately 30 miles south of the wind farm.

This image from April 1, 2009 displays the location and reflecdtivity of the wind farm 30 miles north of the radar site. Credit: NOAA

Doppler radar functions to detect atmospheric phenomena by sending out an electromagnetic signal and simultaneously “listening” for the signal to return if it is bounced off of an object.  Many objects will reflect the radar beam, most notably rain droplets, ice crystals, and snowflakes.  But as we reported earlier this year, doppler radar can also detect bats, birds, aircraft, surface traffic, and even tragedies like 9/11 and the Columbia disaster.  They are even believed to have the potential to alter the weather.

In the case of the Butler Ridge wind farm, the radar beam is being reflected by the large blades on the spinning turbines.  This electromagnetic energy is then reflected back to the radar dome and the radar detects the object.  The turbine blades then appear on the radar image.  This seemingly innocuous interference could have significant ramifications in the upcoming severe weather season though.

This image from the National Weather Service demonstrates how wind turbines can be mistaken for storms on doppler radar. Credit: NOAA

Doppler radar is arguably one of the most critical tools at the disposal of the National Weather Service when they look to provide timely watches and warnings of severe thunderstorms and tornadoes.  By examining the output of doppler radars, meteorologists are able to detect and forecast thunderstorms that may become severe and where they may track.  But if the radar image is masked by interference such as the wind turbines, it is feared that severe weather watches and warnings may be less robust.

The National Weather Service Radar Operations Center has enlisted the help of the wind energy industry to try to alleviate these problems in the future by locating the wind farms in places that would not interfere with such radar signals.  They have published an extensive analysis of the problem.  The map below displays the locations (in red) of the doppler radar sites that may be impacted.  The yellow regions are those in which the radar beam travels close enough to the ground that it could be impacted by windmills constructed in those regions.

This map displays the locations of all National Weather Service radar locations (red) and the regions in which the radar beam is low enough to the ground that it may be impacted by windmills (yellow). Credit: NOAA

Meteorologists may be able to write software code that is able to filter out this interference, but such work can be costly and time-consuming.  The primary concern is that filtering the data to remove such interference may also increase the risk of filtering out true radar echoes – those of actual storms that must be detected for public safety.

With the mushrooming popularity of wind energy around the country, this problem is one that is sure to warrant further study and creative mitigation attempts.