What are the four different cloud groups and how are they classified?

1. High clouds—composed almost entirely of ice crystals, the bases of these clouds start at 16,500 feet (5,032 meters) and reach 45,000 feet (13,725 meters).

2. Cirrus —thin feather-like crystal clouds in patches or narrow bands. The large ice crystals that often trail downward in well-defined wisps are called mare's tails.

3. Cirrostratusis—a thin, white cloud layer that resembles a veil or sheet. This layer can be striated or fibrous. Because of the ice content, these clouds are associated with the halos that surround the sun or moon.

4. Cirrocumulus—thin clouds that appear as small white flakes or cotton patches and may contain super-cooled water.