Rain an occluded front, with thunderstorms possible, but usually their passage is associated with a drying of the air mass. Occluded fronts usually form around mature low-pressure areas. What separates rainfall from other precipitation types, such as ice pellets and snow, is the presence of a thick layer of air aloft which is above the melting point of water, which melts the frozen precipitation well before it reaches the ground. If there is a shallow near surface layer that is below freezing, freezing rain (rain which freezes on contact with surfaces in subfreezing environments) will result. Hail becomes an increasingly infrequent
Ice pellets a solid mass unless mixed with freezing rain. The METAR code for ice pellets is PL (PE before November 1998). Ice pellets are known as sleet in the United States, the official term used by the U.S. National Weather Service. However, the term sleet refers to a mixture of rain and snow in most Commonwealth countries, including Canada. Because of this, Environment Canada never uses the term "sleet", and uses the terms "ice pellets" or "wet snow" instead. Ice pellets form when a layer of above-freezing air is located between above the ground, with sub-freezing air both above and below