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UNIT 4

Weather Causes (3)

SECTION 7. CLOUDS

1. General

Cloud types are classified by their method of formation, their com-position, and the
altitude at which they are found.
2. Cloud Types

a. Cumuliform (Cu). Cumuliform clouds are formed by vertical currents in unstable
air. They are called cumulus and are characterized by their rounded tops which are
pulled upward by the rising air currents. In some types, extensive vertical
developments, called towers, extend upward thousands of feet. The name
"cumulus" means accumulation.

Fair weather cumulus (Cu). cumulus clouds form in convective currents and are
characterized by relatively flat bases and rounded tops. Fair weather cumulus do not show
extensive vertical development, and do not produce precipitation. A cumulus may be the first
step in the development of cumulus-type storm clouds or cumulus-type rain clouds.

Figure 1