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Concept
Precipitation types
Summary
In meteorology, the different types of precipitation often include the character, formation, or phase of the precipitation which is falling to ground level. There are three distinct ways that precipitation can occur. Convective precipitation is generally more intense, and of shorter duration, than stratiform precipitation. 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. Rain or drizzle which freezes on contact with a surface within a subfreezing air mass gains the preceding adjective "freezing", becoming the known freezing rain or freezing drizzle. Slush is a mixture of both liquid and solid precipitation. Frozen forms of precipitation include snow, ice crystals, ice pellets (sleet), hail, and graupel. Their respective intensities are classified either by rate of precipitation, or by visibility restriction.
Precipitation falls in many forms, or phases. They can be subdivided into:
Liquid precipitation:
Drizzle (DZ)
Rain (RA)
Cloudburst (CB)
Freezing/Mixed precipitation:
Freezing drizzle (FZDZ)
Freezing rain (FZRA)
Rain and snow mixed / Slush (RASN)
Drizzle and snow mixed / Slush (DZSN)
Frozen precipitation:
Snow (SN)
Snow grains (SG)
Ice crystals (IC)
Ice pellets / Sleet (PL)
Snow pellets / Graupel (GS)
Hail (GR)
Megacryometeors (MC)
The parenthesized letters are the shortened METAR codes for each phenomenon.
Precipitation occurs when evapotranspiration takes place and local air becomes saturated with water vapor, and so can no longer maintain the level of water vapor in gaseous form, which creates clouds. This occurs when less dense moist air cools, usually when an air mass rises through the atmosphere to higher and cooler altitudes. However, an air mass can also cool without a change in altitude (e.g. through radiative cooling, or ground contact with cold terrain).
Official source
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