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Orographic precipitation occurs when moist air is forced upwards over rising terrain and condenses on the slope, such as a mountain. Precipitation can fall in either liquid or solid phases, is mixed with both, or transition between them at the freezing level. Liquid forms of precipitation include rain and drizzle and dew.
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. [1] The main forms of precipitation include drizzle , rain , sleet , snow , ice pellets , graupel and hail .
Precipitation can be divided into three categories, based on whether it falls as liquid water, liquid water that freezes on contact with the surface, or ice. Mixtures of different types of precipitation, including types in different categories, can fall simultaneously. Liquid forms of precipitation include rain and drizzle.
Liquid droplets of rain that become supercooled while falling through a sub-freezing air mass and then freeze upon impact with any surface they encounter; the resulting glaze ice can accumulate to a thickness of several centimeters. Unlike mixed rain and snow, ice pellets, and hail, freezing rain exists entirely as a liquid until it hits a surface.
The strength of the water cycle and its changes over time are of considerable interest, especially as the climate changes. [26] The hydrological cycle is a system whereby the evaporation of moisture in one place leads to precipitation (rain or snow) in another place. For example, evaporation always exceeds precipitation over the oceans.
Where freezing rain forms when frozen precipitation falls through a melting layer and turns liquid, freezing drizzle forms via the supercooled warm-rain process, in which cloud droplets coalesce until they become heavy enough to fall out of the cloud, but in subfreezing conditions. [2]
The lack of rain in the Northeast has been rather remarkable. New York City and Wilmington, Delaware, are just two cities where only a trace of rain has fallen for the entire month of October so far.
Lake-effect rain, or bay-effect rain, is the liquid equivalent of lake-effect snow, where the rising air results in a transfer of warm air and moisture from a lake into the predominant colder air, resulting in a fast buildup of clouds and rainfall downwind of the lake. [1]