Clouds form when water vapor condenses into tiny water droplets or ice crystals. The process begins when warm air rises and cools. As the air cools, it can hold less water vapor. The excess water vapor condenses into tiny water droplets or ice crystals, forming clouds.

Clouds are associated with rain when the water droplets within the clouds become too heavy to stay suspended. This can happen when the water droplets collide and merge with each other, or when they are weighed down by ice crystals. When the water droplets become heavy enough, they fall from the sky as rain.

The type of rain that falls depends on the temperature of the air and the cloud. When the air is warm, rain can fall as a steady drizzle or as heavy showers. When the air is cold, rain can fall as sleet, hail, or snow.