Any time the droplets in clouds grow and come together to form drops that are large enough to create a speed of falling that is greater than the speed at which the cloud is blowing upward, then they head downward, and if they make it down without evaporating, people on the ground experience them as rain or snow. Sometimes rain evaporates again and heads back up into the clouds. The greater the amount of water vapor under the cloud and the stronger the winds on the updraft, the more likely precipitation becomes