The cloud formation process starts off when air parcels are forced to rise, cool and condense. Mostly, it is composed of a large number of tiny water droplets or ice crystals which are too light to fall. In warm clouds, droplets can form and grow precipitation through (1) condensation in a highly-saturated environment and (2) through colliding and coalescing with other cloud droplets. This process is known as collision-coalescence process. On the other hand, ice crystals can be form through a process known as the Bergeron process which only happens in cool and cold clouds. It needs water vapor, ice crystals and supercooled water drops that must be of equilibrium with the vapor. The ice crystals will gain water vapor from its neighboring droplets and grow to viable size for precipitation.