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the right shape for ice crystals to develop on them. Snowflakes, with their sixsides, are an expression of this hexagonal crystal form of ice.
Cloud types are based on location and shape. In terms of shape, they can be
cirriform, or wispy clouds, stratiform, or layered clouds, or cumuliform, or
clouds formed by rising air. High clouds are made of ice, not water, and are
usually found above 6000 meters. These are mostly cirrus, which are thin and
wispy cirriiform clouds. Cirrus clouds have very little water in them and do not
produce precipitation. Middle clouds are mostly between 2000 and 6000
meters and here it is warm enough for liquid water. Stratus clouds are often in
thick layers that can cover the whole sky. Altostratus are found at these
heights. Stratus can also be low clouds, found under 2000 m. At any height,
you may find cumuliform clouds, formed by rising air. Cumulus clouds are the
puffy, cotton-ball types. If conditions are right, these generate thunderstorms.
Nimbus is the term associated with rain, so cumulonimbus clouds are cumulus
clouds producing rain and nimbostratus are stratus clouds producing rain. Precipitation
Most water drops in clouds are small enough that they stay suspended in the air.
They have to grow a lot in order to be heavy enough to fall. Drops may run into
each other and coalesce into larger drops and this dominates rainfall in warm
clouds of the Tropics and sometimes in the mid-latitudes. In colder clouds,
though, snow forms by ice crystals gaining ice from the water vapor in the air Atmospheric Moisture:5
and by colliding with supersatura...
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- Fall '08