Cloud Definition:

A cloud is a hydrometeor consisting of minute particles of liquid water or ice, or of both,suspended in the free air and usually not touching the ground. It may also include larger particles of liquid water or ice as well as non-aqueous liquid or solid particles such as those present in fumes, smoke or dust.

- (WMO-407 International Cloud Atlas)

Different processes in the atmosphere produce clouds in varying forms and are responsible for much of the weather we experience. Identifying the cloud types indicates what processes in the atmosphere are taking place, allowing an assessment of the present and expected weather to be made. An incorrect identification of cloud type can lead to an incorrect assessment of the weather situation. The observer's responsibility in this respect cannot be over emphasised.

Altocumulus catellanus
Altocumulus castellanus: the presence of this cloud is a sign of instability at its level. When it aquires a considerable vertical extent, it becomes Cumulus congestus, and sometimes Cumulonimbus (the cloud associated with thunderstorms).