(Yellowstone National Park)

This week, the National Weather Service (in Boulder) and National Park Service (in Yellowstone) captured wonderful examples of the sky doing its best impression of the ocean. They photographed rare atmospheric wave clouds, forming from a phenomenon known as Kelvin Helmholtz instability.

The instability arises from a difference in the density of air in adjacent layers and the resulting wind shear. These clouds are extremely short-lived, and break in the same fashion as a wave on a shore – the bottom layer of water moves slower than the top layer, and the top billows over and crashes.