Clouds vary in shape according to their height and temperature, and they contain minute drops of water or ice particles or a combination of both. And, of course, their formation is greatly affected by wind changes.
There are basically three groups of clouds: high clouds between 17,000 and 45,000 feet (cirrus, cirro-cumulus and cirro-stratus); middle clouds between 7,000 and 23,000 feet (alto-cumulus, alto-stratus and nimbo-stratus); and low clouds up to 7,000 feet (strato-cumulus, stratus, cumulus and cumulo-nimbus).
Their height and temperature decide how much pressure is exerted on them by the atmosphere. Finally, the shapes of clouds differ according to the time of day. Towards evening clouds tend to thin out, rise a little and flatten out.