As more water condenses onto existing water droplets in the cloud, the droplets expand. Even with internal updrafts, they eventually become too heavy to remain suspended in the cloud and descend to Earth as rain. Ice crystals form in clouds when the temperature is below freezing (32 °F or 0 °C); snow is created when the temperature is below freezing all the way to the ground. However, you get other types of precipitation if the atmospheric layers within the cloud and between the cloud and the ground vary between warmer than freezing and colder than freezing.
For instance, if a snowflake falls through a warmer region of the cloud, it may become wet and then become frozen again as it is thrown back into a colder region. It may continue indefinitely, accumulating ever-increasing layers of fresh ice. Hail is what ultimately falls when it is too heavy to stay up. The hail stones can get rather large if the updrafts in a thunder cloud are powerful enough before they become too heavy to stay up.
As the carriers of water from one location on Earth to another, clouds are a crucial component of the water cycle. The amount of energy absorbed and trapped in the atmosphere is likewise dependent on these factors. Thus, they play a critical role in modifying the Earth's surface and atmosphere's temperature. More water can be held in the air the warmer it is.
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