Primary objective of this lecture is to present on Formation of Clouds. Clouds are formed when air containing water vapor is cooled below a critical temperature called the dew point and the resulting moisture condenses into droplets on microscopic dust particles (condensation nuclei) in the atmosphere. Clouds are formed in four process: Cirrus; Stratus; Cumulus and Nimbus. Two basic ways precipitation forms: Collision” process (warm clouds) and “Ice Crystal” process (cold clouds).