Cloud Type: Kelvin-Helmholtz Instability Wave Clouds
Look like: Wave silhouettes
They form when: Air flows in the same direction but at two different velocities with a cloud present.
Why they're so rare: They're normally invisible unless the right temperature and moisture combination is present. This makes wave clouds a big catch for cloud spotters.
Chance of spotting in a year: Slim to noneShare this on Facebook?