The main premise behind this process is that ice crystals and super-cooled liquid water droplets coexist in the higher part of the cloud. Heavy showers fall from cumuliform clouds because these clouds contain large and shifting convection currents and move quickly by. Steady precipitation falls from stratiform clouds because these cover a large area and have relatively small convection currents. Freezing rain consists of precipitation that falls through a cold layer of the atmosphere. If the cold layer is not thick enough to freeze the droplets, it will cause them to become super-cooled, allowing them to freeze immediately on contact with the ground or an object.
Sleet begins as a snowflake which falls through a warm layer of the atmosphere.
It partially melts, then falls through a thick cold layer and refreezes into a small pellet of ice, which is called sleet. Sleet is formed when a snowflakes falls through warm layer and melts, and then falls through a cold layer and refreezes. Hail is formed by updrafts in cumulonimbus clouds. These updrafts circulate frozen raindrops or graupel up into regions of super-cooled droplets. Each time the hailstone circulates through the cloud, it gains another layer of ice by accreting these droplets.