Cirrus Clouds

Cirrus clouds over a winter landscape

Lisa Gardiner

Cirrus clouds are made of ice crystals and look like long, thin, wispy white streamers high in the sky. They are commonly known as "mare's tails" because they are shaped like the tail of a horse. Cirrus clouds are often seen during fair weather. But if they build up larger over time and are followed by cirrostratus clouds, there may be a warm front on the way.