Billow clouds look like ocean waves in the sky

By GRAHAMUK at the English language Wikipedia, CC BY-SA 3.0, Link

Kelvin-Helmholtz clouds, also known as  ‘billow clouds’, look like rolling ocean waves in the sky. The clouds often form on windy days, when two air currents of varying speeds meet in the atmosphere. It’s believed that this kind of clouds inspired the swirls in van Gogh’s ‘Starry Night‘.

Brocken Inaglory [CC BY-SA 3.0], via Wikimedia Commons

Brocken Inaglory [CC BY-SA 4.0], via Wikimedia Commons