LOCAL WIND FARMS INTERFERE WITH NWS DOPPLER RADAR

Written by: Brian Neudorff

It is a clear day, maybe just a few clouds yet no rain, but when you look at the radar, there appears to be some kind of storm sitting over the western and southern parts of Wyoming county, but it's not rain. What is it?

These bright reds, oranges and yellow colors displayed on a radar map are interference caused by wind farms that have recently been erected in Wyoming county.

These wind farms are 25 to 30 miles southeast of the National Weather service Doppler radar in Buffalo, New York. These turbines stand 265 feet tall, with blades extending an additional 123 feet (giving them a diameter of nearly 400 ft), because of their close proximity and elevation above the radar site they are with in the radar line of site (RLOS) of the NWS Doppler radar.

Here is what is happening, part of the radar beam that gets sent out from the NWS radar is being reflected back to the radar by the rotating turbines. The radar interprets this "returned energy" as an area of precipitation and plots it accordingly on the map. This contamination of the base reflectivity image as illustrated in the image above, has an effect on the radar software used to estimate rainfall and to detect certain storm characteristics. (You can learn more about how the Doppler Radar works here.)

Because a Doppler radar was designed to detect movement or velocities with in a storm the rotating turbines can produce erroneous data. Velocity data is used by radar operators and software with in the radar to detect certain storm characteristics such as rotating storms, possible development of a tornado, and the direction and speed of a particular storm or line of storms.

The Doppler radars used by the NWS have filters on them that allow them to cancel out the interference from terrain,buildings, and other structures that have no movement. Unfortunately, the radar sees the rotating wind turbine blades as targets having reflectivity and motion, displays them as weather on the map.

This interference is not limited to western New York, in fact there are several sites across the country where wind farms are being detected by local NWS Doppler radar. This interference can have several impact on how weather information and warnings are issued by the National Weather Service including:

• Thunderstorm or winter storm characteristics could be masked or misinterpreted, reducing warning effectiveness in the vicinity of, and downrange of the wind farm.
• False signatures contaminating Doppler velocity data in the vicinity and downrange of the wind energy facility could reduce forecaster's situational awareness, particularly during hazardous/severe weather events.
• Data masking or contamination if thunderstorms develop over the wind farm may negatively impact warning effectiveness.
• False precipitation estimates could negatively impact flash-flood warning effectiveness.

The National Weather Service Radar Operations Center (ROC) is working with the wind energy industry and developers to try and alleviate any future problems or interference by building future wind farms in locations that would not interfere with local NWS Doppler radar or keep them out of the radar line of site. The NWS ROC has published an extensive analysis on how wind turbines impact NEXRAD Doppler weather radar. The map below shows all the NEXRAD radar site (indicated by the red dot) and the yellow regions around the red dot are the areas where the radar beam is close enough to the ground that a wind turbine and wind farm could cause interference if they were built in those areas.



For more information on how wind turbines impact Doppler weather radar, check out the ROC website.