LINCOLN, Ill. (WCIA) – As debate continues in Springfield over wind farms and the impacts they have, questions remain about how wind farms impact the National Weather Service’s radar sites, including the one just outside of Lincoln.

WCIA reached out to the National Weather Service Office in Lincoln about the issue.

Ed Shimon, the Warning Coordination Meteorologist for the National Weather Service Office in Lincoln said they were able to issue a tornado warning over twenty minutes ahead of the Maroa tornado.

That helped give people timely information to seek shelter from the danger.

They say that Storm Spotters are crucial in helping with that process.

“It’s always great to have spotters that are able to track those and give us ground truth as these things approach,” said Shimon.

The thunderstorm that produced five tornadoes as it tracked from Illiopolis to Gibson City was able to be detected by the doppler radar.

Map of eight confirmed tornadoes in Central Illinois on 1/3/23

But some of the data made available to meteorologists at the National Weather Service and the general public was contaminated by the presence of the wind farm.

“The data from the doppler radar on the lowest level of the storm was contaminated,” said Shimon.

“But that’s just one part of the total operations concept, where we use the environment, storm spotters and radar all together as a team.”

While sometimes storm circulations can be shallow and only a few thousand feet high, normally the radar can detect it at a higher level which allows them to provide a proper severe weather warning. And the presence of wind farms won’t change how the National Weather Service monitors storms.

“While we’re watching storms, as they approach and go through wind farms, we know where the wind farms are and we always use all the resources available,” said Shimon.

How Radar Works:

Each of the 159 National Weather Service Radars across the country scan multiple levels of the atmosphere as the radar rotates around.

The radar antenna emits extremely short bursts of radio waves, called pulses which are then reflected back as they hit targets in the atmosphere.

These targets are often rain, snow, sleet, ice or hail.

However, sometimes, these are able to detect non-meteorological targets, such as birds, insects, traffic on freeways, buildings and even wind farms.

Prior to the advancements in Doppler Radar technology, data was only collected at one scan level, measured in degrees based on the angle of the radar beam above the earth.

Today, the radar beam is able to sample multiple levels rapidly, allowing for data to be detected at many levels of the atmosphere.

Wind Farms and Radar: Not a New Problem

The detection of wind farms by doppler radar has led to questions about how wind farms impact the ability for tornadoes to be detected.

On December 1st, 2018, the National Weather Service in Central Illinois tracked a supercell thunderstorm that tracked through Taylorville, Illinois.

As that tornado moved through Taylorville and to the northwest, the National Weather Service states that at 6:11 p.m., strong rotation indicated a tornado was possible on a supercell thunderstorm just northwest of Decatur, Illinois.

By 6:30 p.m., radar did not show the presence of rotation, but an EF-1 tornado was present and ongoing at that time near Maroa.

The tornado occurred in a wind farm in northern Macon County which contaminated the data and obscured the tornado and the apparent rotation.

As the storm moved out of the wind farm, by 6:34 p.m., strong rotation again became evident on radar as the parent supercell thunderstorm exited the wind farm.

Graphic posted by National Weather Service in Lincoln about the 12/1/2018 Tornado Outbreak and a tornado in Macon County obscured by wind farms

“The Taylorville event, there was a bit more of a obscuration, a bit more contamination of the half degree slice,” said Shimon.

That’s the lowest angle that the radar beam samples, providing information about a storm in a section that is closest to the ground.

“But, even in that case, the slices above that were at least able to give us some picture of what was happening.”

It’s not the only time interference of doppler radar has occurred in the presence of wind farms.

In the most recent tornado outbreak that included two tornadoes in the Maroa area, the wind farms did impact the available data to the National Weather Service.

The data contamination was noticed by meteorologists at the National Weather Service Office in Lincoln on the lowest two levels of the radar.

As the tornadoes touched down, those lowest levels of radar data did not indicate the presence of very strong rotation. That data is sampled from the atmosphere at 1,200 and 2,000 feet above the ground, well above the physical height of the wind farms at that location.

“We were able to utilize data above the lowest two level scans to see rotation was present in that thunderstorm,” said Shimon.

Having spotter reports and reports of tornadoes outside the wind farm still allowed the National Weather Service to issue warnings in the affected area.

While the data was contaminated and did not clearly show the presence of the tornado in the lowest scans, other scans and confirmed reports on the ground helped their decision-making process.

“The wind farms do impact radar beams, but we have so many different scan strategy levels that we really make it almost a seamless process so that we don’t let the wind farms impact our decision making process during hazardous weather events,” said Shimon.

Even still, the National Weather Service does rely on those lower scans for the most accurate data. That’s closest to the ground where tornadoes occur. And, thunderstorms don’t always rotate with the same strength from the top of the storm to the bottom.

“The mesocyclone that was visible [on January 3rd] was a couple of slices above ground level. Sometimes that’s the case just based on the intensity of the mesocyclone. It’s not always a cone of constant rotation from the base of the storm to the top. And finding that peak rotation sometimes take a little bit of an effort to go through all the slices and make sure you’re seeing the full picture.”

And when spotters aren’t present and storms aren’t as visible due to weather conditions or time of day, that can lower their confidence, something where all those factors helped the decision-making for the tornado on January 3rd.

“We always were looking at the lowest four scans, or the scans that were going to be most effective for a particular day, depending on where storms are in relation to the radar. And we have multiple radars that we always look at,” said Shimon.

For different locations, different radar angles will lead to different outcomes in data. From the National Weather Service in Lincoln radar site, in Macon County, the lowest elevation scan will see between 1,000 and 1,500 feet above the ground. But the lowest elevation scan over Champaign Urbana measures around 4,500 feet above, and over Danville at over 8,000 feet up.

For meteorologists, storm spotters and emergency management officials, the lower level data provides the best sampling of the storm, as stronger rotation detected lower in the storm increases the confidence that a tornado could form.

Radar Beam affected by more than Wind Farms

“The radar is obviously susceptible to all sorts of environmental interferences. Ground clutter comes whether its a wind farm or not. We’ve had buildings, we’ve had a lot of things that come into play with radar images.

But the difference between many of those objects and wind farms lies in how those wind farms move, or spin.

The rotation of the turbines impact not only reflectivity data, but also velocity data based on how the windmills reflect pulse energy back to the radar and how the rotating turbines also impact velocity data.

Even on a clear day, interference by wind farms can be see on doppler radar. The radar will show false echoes indicating precipitation is present, even when there is no precipitation present.

“Most of the time, the beam of the radar is at the mercy of the atmosphere in the environment. Where are the inversions? How is the temperature changing with height that kind of controls where that beam goes instead of it normally curving up and away at a steady rate? Sometimes you get a little bit more of an inversion and it kind of hugs the ground a little more. That’s a key thing because sometimes on our radar, on a strong inversion day, we’ll see ground clutter all the way up to 150 miles away from the radar. It just depends,” said Shimon.

Radar imagery via Radar Scope showing contamination of radar data where a wind farm is present when no storms are around.

This normally happens in the lowest levels of the atmosphere where the radar beam scans the lowest in the atmosphere.

Those radar beams closest to the ground are arguably the most important radar beams to detecting rotation; if a storm is rotating closer to the ground, it can be more likely to produce a tornado.

In most situations, algorithms encoded in the process can help to filter out the wind turbines, but sometimes the contamination is too strong for the algorithms to process.

Because the rotating wind turbine blades are reflecting back pulse energy both by being present and having motion, these returns show up on doppler radar systems.

It’s the expertise at the National Weather Service that they train for these types of data contamination.

“People are going to think there is something is there that may not be there in terms of the wind farm. Most of the time, that’s usually what happens is people think there’s a storm on radar because there’s a return where a wind farm is. And in most cases, there’s nothing. A lot of times people that look at radar are not as adept to what ground clutter is. We can tell immediately where ground clutter is occurring so that we know what the situation is as the radar images come back to us, so we can make sure we’ve got the best picture to make our decisions for warnings,” said Shimon.

Research Center works to understand, lessen impacts from wind farms

The National Weather Service Radar Operations Center (ROC) provides guidance based on the possibility of interference with zones that are circled out away from doppler radar sites.

These zones are based on several factors, including the height of wind mills, elevation and more.

A no build zone exists around 2.5 miles around any given doppler radar site. This no-build area can severely impact the radar and even damage the wind turbine tower based on the energy being pulsed out from the radar site.

A mitigation zone exists up to 10 miles out. This zone is named as the ROC states that wind farms with a 524 foot (160 meter) high turbine this zone “have the potential for moderate to high impacts” and the ROC will work wit hthe developer to get detailed project information, do a thorough impact analysis and discuss mitigation solutions.

The latest proposed Logan County Wind Farms lie in this range, and a mitigation agreement that allows the National Weather Service to request shutting down the turbines during inclement weather was signed.

A consultation zone exists within 10 to 20 miles and a notification zone exists within 20 to 30 miles where developers are encouraged to work with NWS and the ROC, but impacts are expected to be lower, albeit still possible.

Bill Ward, a meteorologist with the Radar Operations Center says that they plan to work with developers to understand the impacts and how it could affect operations for the weather enterprise.

“We always want to talk to developers and analyze a wind farm proposal before it goes up. If it is likely to cause severe impacts we’ll request that they do not build. Then, we’ll start to look at the impacts beyond the no-build zone and see how it affects radar operations and make requests to help lessen impacts,” said Ward.

But as wind turbines grow taller and blades grow longer, questions still remain on how taller wind mills will impact doppler radar sites.

And as more tornadoes touch down in wind farm sites, the ROC will work with researchers, educational institutions and local National Weather Service offices to further understand how wind farms are affecting radar sites.

Wind Farms: An Evolving Discussion

With new guidance from the Federal Government promoting clean energy and pushing for a reduction in greenhouse gases, wind farms are a part of meeting that goal.

And that means more wind farms, especially in areas that are ideal for wind energy, including right here in Central Illinois.

As newer, taller wind farms are built, impacts will continue to be assessed, studied and seen on the local Doppler Radar site.

But regulations and control are limited in dealing with such potential impacts.

The Radar Operations Center’s guidance is just that, guidance that recommends what developers should do.

But without legislative or regulatory power, these wind farm mitigation efforts could sour quickly.

That’s the case in Logan County, where a proposed wind farm was passed in 2022.

Guidance from the ROC suggested that radar contamination from wind farms could not only occur in those areas where the wind farms were built, but also as far as 25 miles downstream from the wind farm.

That includes a sizeable portion of Central Illinois, and impacts thousands of residents, potentially lingering into Decatur, Illinois, a population of almost 70,000 residents with a history of tornadoes, including one on the same day as the Maroa tornadoes.

If data was contaminated further downstream from taller wind farms being built closer to doppler radar sites, that could pose safety problems for residents even well away from wind farm developments.

But the Logan County Board passed the wind farm proposal after an agreement was reached between the developer and the National Weather Service.

That agreement was a mitigation proposal that allows the National Weather Service Office to request a wind farm developer shut down wind farm turbines in the presence of severe weather.

Emily Davenport, Logan County Board President said there is no federal regulation present that prevents wind turbines from being built within a mitigation zone.

The role of contractual agreements signed between a National Weather Service Office and a wind farm developer remains uncertain without legal backing at the state or federal level or repercussions to a developer failing to adhere to the contract.

And the National Weather Service has no authority to tell developers to not build turbines based on their guidance.

“Our role is not to approve or disapprove of wind farm projects in the United States. Instead, we advise developers at early planning stages on strategic placement and mitigation to minimize impacts to radar data,” the National Weather Service said.

The Logan County Board included a provision fining the parent company $5,000 per incident if a violation occurred, a provision that was also used in De Witt County in a previous proposal.

As more wind farms are approved, the discussion will only continue, and the research will continue to account for these changes.