Rain is formed when warm, moist air rises and meets colder air high in
atmosphere. The water vapor condenses and forms precipitation
that falls to the ground causing rain.
Experiment: Try this out!
Pour about two inches of very hot water into a glass mayonnaise
or canning jar. Cover the jar with a plate and wait a few minutes.
Place some ice cubes
of the plate. The cold plate causes the moisture in the warm air which is
inside the jar to condense and form water droplets. This is the
same thing that happens
in the atmosphere causing rain.