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Clouds are classifies on a basis of their

form and height


high, white, thin


cloud masses that consist of rounded individual masses


sheets or layers that cover most or all of the sky

High clouds

cirrus, cirrostratus, cirrocumulus


flat layers of clouds


consist of fluffy masses

Middle Clouds

Altocumulus, Altostratus


consist of rounded masses

Altocumulus clouds differ from cirrocumulus clouds in that

altocumulus clouds are larger and denser


create a uniform white to gray sheet that covers most to all of the sky with the sun or moon as a visible bright spot.

Low clouds

stratus, stratocumulus, nimbostratus


have a scalloped bottom that appears to be long parallel rolls or broken rounded patches.


Main precipitation makers


a cloud with its base at or very near the ground.

Fog caused by cooling

As the air cools, it becomes denser and drains into low areas such as river valleys, where thick fog accumulations may occur.

Fog caused by evaporation

When cool air moves over warm water, enough moisture may evaporate from the water surface to produce saturation.

For precipitation to form

cloud droplets must grow in volume by roughly one million times

The Bergeron Process

A scientific theory that relates the formation of precipitation to supercooled clouds, freezing nuclei, and the different saturation levels of ice and liquid water.

Supercooled Water

is the condition of water droplets that remain in the liquid state at temperatures well below 0oC.

Supersaturated air

is the condition of air that is more concentrated than is normally possible under given temperature and pressure conditions.

Collision- coalescence process

a theory of raindrop formation in warm clouds (above 0oC) in which large cloud droplets collide and join together with smaller droplets to form a raindrop.

The type of precipitation that reaches Earth's surface depends on

the temperature profile in the lower few kilometers of the atmosphere.


drops of water that fall from a cloud with diameters of at least 0.5 mm.


At very low temperatures (when the moisture content of air is low) light fluffy snow made up of individual six-sided ice crystals forms.


the fall of clear to translucent ice

Hail is produced in

cumulonimbus clouds

Hailstones begin as

small ice pellets

Hailstones grow

by collecting supercooled water droplets as they fall through a cloud

100º C

Water's boiling and condensing point

0º C

Water's freezing and melting point

A psychrometer measures what in addition to relative humidity

dew point

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