If you’ve ever looked up and seen the sky rippling like a stormy sea, you may have witnessed one of the most dramatic and rare cloud formations in the atmosphere: asperitas clouds.

With their dark, churning underbellies and wavelike appearance, asperitas (Latin for “roughness”) look like the atmosphere has turned upside-down.

Asperitas clouds were officially recognized as a distinct cloud type in 2017, making them one of the newest additions to the World Meteorological Organization’s International Cloud Atlas.

Weather in your inbox

Forecast Location

Sign Up

By signing up you agree to the Terms & Privacy Policy. Unsubscribe at any time.

While they can appear ominous and turbulent, asperitas are not necessarily a sign of severe weather. However, they do form most often ahead of a thunderstorm or when atmospheric instability is present.

The undulating, textured look of asperitas is likely shaped by wind shear and gravity waves, which are invisible oscillations in the atmosphere that can distort clouds into dramatic patterns. Their eerie, cinematic appearance has made them a favorite among storm photographers and skywatchers, often mistaken for the opening scene of a sci-fi film.

Though rare, asperitas clouds are a powerful reminder that the sky is constantly in motion.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.