Top 10 Unusual but Fascinating Cloud Formations
Clouds can generally be classified by appearance – cumulus (heap), stratus (layer), cirrus (curl), nimbus (rain) – or by height of cloud base – high level, mid level, low level clouds and clouds with vertical development. I’ve gathered in this Top 10 list some of the strangest, most  beautiful cloud formations:
The Kelvin-Helmholtz Wave Cloud

The Kelvin-Helmholtz wave cloud looks like crashing ocean waves. These beautiful clouds are named after German physicist Hermann von Helmholtz and British physicist Lord Kelvin, because they form when two different layers of air are moving past each other at different speeds. The above layer is faster. Some parts of the boundary – a shearing layer – move down, and others move up.