Clouds
Clouds are formed when the temperature reaches the condensation point and water vapor in the air turns into liquid (or ice).
Clouds are usually classified in four main categories according to the level:
- High clouds: Cirrus, Cirrostratus and Cirrocumulus
- Middle clouds: Altocumulus and Altostratus
- Low clouds: Stratus, Nimbostratus and Stratocumulus
- Vertically growing clouds or multi-level clouds: Cumulus and Cumulonimbus
Other categories are:
Scud, Lenticular, Mammatus and Artificial or man made clouds (for exampel Jet contrails).

As with all human classification of natural phenomena one has to remember that there can be forms that will fall between given categories and forms that can fit into several classes.
High Clouds

Cirrostratus

Cirrus

Cirrus

Cirrocumulus
Middle Clouds

Altocumulus

Altocumulus

Dissolving Altocumulus

Low Clouds

Nimbostratus

Nimbostratus

Stratus

Stratocumulus
Multi-level Clouds

Cumulus

Cumulus

Cumulonimbus

Pictures of mixed types of clouds.

Cirrus, Cumulus, Artif.

Altocum, Cirrus

Cumulus, Altocum.

Stratocum, Altocum.

© J. Käld

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