Precipitation Processes and Types

Abstract

Two processes generate precipitation: Either liquid water droplets collide and coalesce with each other until they grow too large to be supported by gravity, or liquid water in the cloud evaporates, which in turn deposits onto ice, allowing droplet growth as snow, in the Wegener-Bergeron-Findeisen (aka: three-phase) process. In the three-phase process, the snow may remain in its original form all the way to the surface, or it may melt to become rain. It may also melt and refreeze before hitting the surface, to become sleet, or it may melt and refreeze only on contact with the surface (freezing rain). The formation process of hail in a cumulonimbus cloud is also explained. Changes in precipitation patterns are expected as the climate continues to change in the future.