Refer to figure.
Coalescence theory describes the process of precipitation formation in clouds above 0ºC. Initially, water droplets form uniformly during condensation. Updrafts within the cloud lift these droplets, causing them to collide and merge with others. These collisions lead to the droplets growing larger until they become too heavy to remain suspended and fall as precipitation. During their descent, further collisions may cause them to increase in size. The final size of the precipitation droplets depends on the strength of the upward air currents within the cloud: stronger uplift results in larger droplets.