Parts of the Front Range were treated to a rare meteorological sight on Sunday evening.
Clouds that took on the shape of rolling ocean waves were visible from the Denver metro area just before sunset.
The clouds are known scientifically as Kelvin-Helmholtz clouds, named after the two scientists who studied them in the 1800s.
These "wave cloud" formations develop when there's strong wind shear present between two air streams. Basically, what we have is wind that is blowing much stronger in the upper levels than in the lower levels of the atmosphere. Faster wind on top of the clouds gives the visual of breaking waves in the sky, or a billowing wave pattern.
The clouds usually form on windy days, when the atmosphere is more unstable. It's also a sign to pilots of turbulent skies.