Clouds that look like waves are rare and beautiful. These clouds – known as Kelvin-Helmholtz clouds, billow clouds, or shear-gravity clouds – might have been the inspiration for Van Gogh’s painting Starry Night. The next time you spot one of these remarkable wave clouds, capture a photograph and submit it to us!
Kelvin-Helmholtz clouds are named for Lord Kelvin and Hermann von Helmholtz, who studied the physics of the instability that leads to this type of cloud formation. A Kelvin-Helmholtz instability forms where there’s a velocity difference across the interface between two fluids: for example, wind blowing over water.
How to see Kelvin-Helmholtz clouds
When might you get to see these beautiful clouds? Your odds are better on windy days, when there’s a difference in densities of the air – for example, during a temperature inversion – when warm air flows over cooler air. You’re also more likely to see these clouds near sunrise or sunset, another time when the bottom of the clouds are cooler and the air above is warmer. The clouds take on this wave shape when the air above is moving more quickly than the air below, pushing over the tops of the clouds and creating the rolling wave appearance. As you might have guessed, Kelvin-Helmholtz clouds are a sign that aircraft in the area will be experiencing turbulence.
“Wave clouds” from the EarthSky community
Bottom line: Clouds that look like waves across the sky are known as Kelvin-Helmholtz clouds. These clouds form from winds moving at two different speeds.