Cirrus clouds form at altitudes of about 6000m (20,000 ft) or more, heights where water droplets freeze form to ice crystals. These clouds are typically formed at the head (or leading edge) of a warm front. Cirrus clouds act as a warning of impending precipitation (warm front). These clouds can spread out for several thousands of kilometers, thus covering continents. Interestingly, other planets can also have cirrus type of clouds. Another interesting aspect of cirrus clouds is the shapes the clouds can attain. Some of the shapes attained by cirrus clouds include, finger-like, comma shaped, plates, columns, mixed shape, etc. Any cloud can convert to cirrus type, provided temperature and pressure conditions are conducive to formation of ice crystals and, indirectly, cirrus type clouds.
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