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Cirrus clouds
Cirrus clouds are thin, wispy clouds that usually
form above 18,000 feet. These clouds are blown by strong westerly winds aloft
into streamers known as "mares' tails" Cirrus clouds generally move
from west to east across the sky and usually "point" to fair weather.
Cirrus clouds form when water vapor undergoes
deposition and forms ice crystals. Cirrus clouds are thin because they form
in the higher levels of the atmosphere where little water vapor is present.
Cirrus clouds over Rockville, Md.
Cirrus clouds over Fort Worth, Texas
Cloud combinations with cirrus
- Cirrostratus: These sheet-like, thin clouds form
above 18,000 feet. Cirrostratus clouds are so thin that the sun and moon can
be seen clearly through the cloud. Sometimes these clouds are so thin that
the only clue to their presence is a halo around the sun or moon. Ice crystals
in cirrostratus clouds bend the light rays from the sun or moon as they pass
through the cloud, which forms the halo around the sun or moon. Thick cirrostratus
clouds give the sky a bright white appearance and often signal rain or snow
within 24 hours, especially if they are followed by mid-level clouds.
- Cirrocumulus: These clouds form above 18,000
feet and appear as small, rounded white puffs that are isolated or in long
rows. When the white puffs are in rows, they give the cloud a rippling appearance
that distinguishes it from a cirrus or a cirrostratus cloud. Cirrocumulus
clouds rarely cover the entire sky. The individual cloud elements that reflect
the red or yellow light of a setting sun make this one of the most beautiful
of all clouds. The small ripples in a cirrocumulus cloud resemble the scales
of a fish, which earned the nickname "mackerel sky".
Cirrocumulus clouds during a sunset in Laurel,
Md.
Photos copyrighted by H. Michael Mogil, HOW
THE WEATHERWORKS
By Chad Palmer, USA TODAY Weather team
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