In 2008, Danish scientists followed strange white trails behind offshore wind turbines to understand what caused them. 18 years later, the research showed that blade-driven air mixing can contribute to shallow fog formation in winter

On February 12, 2008, an unusual sight appeared behind turbines at Denmark’s Horns Rev 1 offshore wind farm. Long white trails stretched behind the machines, prompting scientists to investigate what was happening in the air around the rotating blades. The answer was surprisingly atmospheric. Under particular winter conditions, turbine blades can mix layers of air with different temperatures and moisture levels strongly enough to help shallow fog form, as per a report by Eco News.

But the same turbines can also make existing fog disappear. The effect depends heavily on the weather and conditions at the site.

What created the strange white trails?

At Horns Rev 1, researchers found that cold, humid air was already close to the point where it could condense into fog. As the turbines rotated, their wakes moved warmer, moisture-rich air upward and cooler air downward. That vertical mixing helped the already-saturated air condense, creating visible ribbons of fog behind the rows of turbines.

The conditions were unusually specific. Wind speeds were close to the turbines’ minimum operating threshold, meaning most of the machines were producing relatively little power. The photographs were striking, but the research did not establish that turbine-generated fog happens routinely.

The phenomenon is better understood as a result of atmospheric mixing rather than turbines simply producing fog on demand.

Can offshore wind turbines also clear fog?

A later observation at Horns Rev 2 on January 25, 2016, produced almost the opposite result. In that case, warm, moist air had traveled over cold seawater and formed a shallow layer of advection fog. Turbine-driven mixing then brought warmer, drier air from higher in the atmosphere down into the wake.

Instead of creating more visible fog, that mixing helped disperse it farther downwind. That is why describing offshore turbines as “fog machines” would be misleading. Their blades act more like enormous atmospheric mixers, with the result depending on temperature, humidity, wind speed, sea-surface conditions and the stability of the air before the turbines begin disturbing it.

How does turbine-driven mixing change fog?

Fog develops when air that is nearly saturated cools enough for water vapor to condense into tiny droplets. The turbine wake can alter that process by moving different layers of air around. If it cools and lifts already moist air, fog can become more visible. If it introduces warmer or drier air, the same mixing can weaken or disperse the fog.

The Deltares report cited by Dutch authorities describes the turbines simply as “wind turbines are mixers of the atmosphere,” emphasizing wake turbulence and vertical movement between air layers rather than a straightforward pressure-drop effect behind the blades.

The distinction matters because the effect is highly dependent on local atmospheric conditions.

Why are shipping authorities watching the issue?

The potential impact matters because offshore wind farms are expanding into waters used by commercial and other vessels.

Rijkswaterstaat says offshore wind farms may be associated with faster mist and fog formation, unexpected turbulence and changes in currents or waves near installations.

KNMI and Rijkswaterstaat operate sensors in wind farms, while the Dutch MOSWOZ safety program is examining whether improved forecasts, additional warnings and real-time weather and water information could help reduce risks for vessels.

The scale of the offshore wind buildout makes understanding these conditions increasingly important. A 2025 Dutch policy assessment said the Dutch North Sea had around 700 wind turbines, with approximately 1,700 expected by 2032. Offshore wind areas already covered about 1,470 square miles, or more than 6% of the Dutch sector.

Is fog the biggest danger for ships?

Not necessarily. The documented evidence does not show a widespread pattern of ships suddenly encountering dense fog created from otherwise clear air around offshore wind farms.

Dutch officials have instead highlighted the broader navigational challenge created by expanding turbine arrays. More installations can reduce the space available for ships to maneuver, particularly during bad weather or equipment failures.

Risk analyses cited in the 2025 policy report estimated one to two ship-turbine collisions annually by 2032.

A 2025 MOSWOZ simulator study found no evidence that wind farms inherently harmed crews’ situational awareness. However, traffic density, tighter navigation space, nighttime lighting and narrow passages for smaller vessels presented practical challenges.

The researchers also stressed that the simulator work was exploratory and that more quantitative research is needed before broader conclusions can be drawn.

Could scientists predict when turbines will create fog?

A useful warning system would need considerably more information than a simple humidity reading.

The documented cases suggest that forecasts would need to consider atmospheric stability, air and sea temperatures, wind direction and speed, turbine operation and the depth of any moist atmospheric layer.

Those factors can determine whether a turbine wake is likely to create, intensify or disperse shallow fog.

The scale of turbine wakes is also being studied. A May 2026 satellite study analyzed 7,122 Sentinel-1 radar images and found near-surface wind-speed wake signatures extending more than 60 miles under favorable conditions.

That finding, however, refers to aerodynamic wakes. It does not mean that fog banks extended 60 miles behind turbines.

What does the research tell us?

The clearest conclusion is a cautious one. Offshore wind turbines can influence shallow fog under exceptional conditions, but the available evidence does not show that ships routinely face dense new fog banks produced by turbines from clear skies.

The 2008 Horns Rev observation remains an important example of how turbine wakes can interact with a very specific combination of cold, humid and stable atmospheric conditions. The 2016 case demonstrates that the same basic mixing process can also disperse fog.

As offshore wind farms continue expanding, understanding these local effects becomes increasingly useful for shipping safety.

The issue is therefore less about choosing between renewable energy and safe navigation and more about understanding the microclimate around growing offshore wind installations well enough to provide captains with useful warnings when visibility conditions change.

FAQs

Can wind turbines create fog?
Yes, but only under specific atmospheric conditions.

Can turbines clear fog too?
Yes. Their air mixing can also disperse shallow fog.