Cirrus uncinus cloud

Cirrus uncinus is a type of cirrus cloud. Its name is derived from Latin, meaning curly hooks. Also known as mares' tails, these clouds are generally sparse in the sky, and very thin.

The clouds occur at very high altitudes, at a temperature of about minus 40-50 degrees Celsius. They are generally seen when a warm or occluded front is approaching. They are very high in the troposphere, and generally mean that precipitation, usually rain, is approaching.