(a) Formation of Clouds.
Cloud is formed when the ground is heated by the sun resulting in evaporation and evapo-transpiration. The air is then forced to rise to a higher altitude. The cooling of air with altitude leading to saturation and condensation around the hygroscopic nuclei results in coalescence of particles to form clouds.
(b) Relief
This type of rainfall occurs in mountainous areas. It is common at the coastal areas where highlands lie at right angles I the coast. When moisture laden wind comes into contact with the highland, it is forced to rise. The rising air expands, cools and condenses. Clouds are formed and rain falls at the windward side. Cool dry winds descend at the leeward side and produce little or no rainfall. The leeward slope is also known as rain shadow.