In meteorology, precipitation (also known as one class of hydrometeors, which are atmospheric water phenomena) is any product of the condensation of atmospheric water vapor that is deposited on the earth's surface. It occurs when the atmosphere (being a large gaseous solution) becomes saturated with water vapour and the water condenses and falls out of solution (i.e., precipitates).^[1] Air becomes saturated via two processes, cooling and adding moisture. // Meteorology (from Greek: μετέωρον, meteoron, high in the sky; and λόγος, logos, knowledge) is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting. ... For other uses, see Atmosphere (disambiguation). ... Water vapor or water vapour (see spelling differences), also aqueous vapor, is the gas phase of water. ... Making a saline water solution by dissolving table salt (NaCl) in water This article is about chemical solutions. ... Boundaries: Phase, Pressure, Temperature Evaporation/Sublimation Whenever a water molecule leaves a surface, it is said to have evaporated. ...

Precipitation that reaches the surface of the earth can occur in many different forms, including rain, freezing rain, drizzle, snow, sleet, and hail. Virga is precipitation that begins falling to the earth but evaporates before reaching the surface. Precipitation is a major component of the hydrologic cycle, and is responsible for depositing most of the fresh water on the planet. Approximately 505,000 km³ of water falls as precipitation each year, 398,000 km³ of it over the oceans.^[2] Given the Earth's surface area, that means the globally-averaged annual precipitation is about 1 m, and the average annual precipitation over oceans is about 1.1 m. This article is about precipitation. ... Freezing Rain is a type of precipitation that begins as snow at higher altitude, falling from a cloud towards earth, melts completely on its way down while passing through a layer of air above freezing temperature, and then encounters a layer below freezing at lower level to become supercooled. ... Drizzle is fairly steady, light precipitation. ... For other uses, see Snow (disambiguation). ... Sleet is a term used in a variety of ways to describe precipitation intermediate between rain and snow but distinct from hail. ... This article is about the precipitation. ... Nimbostratus virga In meteorology, virga is precipitation that falls from a cloud but evaporates before reaching the ground. ... The water cycle—technically known as the hydrologic cycle—is the circulation of water within the earths hydrosphere, involving changes in the physical state of water between liquid, solid, and gas phases. ... For the village on the Isle of Wight, see Freshwater, Isle of Wight. ... This article is about the astronomical term. ... Animated map exhibiting the worlds oceanic waters. ... This article is about Earth as a planet. ...

Types of precipitation

A distant storm producing rain

Precipitation that forms aloft is divided into three categories: Image File history File links Metadata Size of this preview: 800 × 600 pixelsFull resolution (2048 × 1536 pixels, file size: 1. ... Image File history File links Metadata Size of this preview: 800 × 600 pixelsFull resolution (2048 × 1536 pixels, file size: 1. ...

• Liquid precipitation;
• Freezing precipitation; and
• Frozen precipitation.

• Types of liquid precipitation:
  • Drizzle (DZ)
  • Rain (RA)

• Types of freezing precipitation:
  • Freezing drizzle (FZDZ)
  • Freezing rain/Sleet (FZRA)

• Types of frozen precipitation:
  • Snow (SN)
  • Snow pellets (SHGS)
  • Snow grains (SG)
  • Ice pellets/Sleet (PL)
  • Hail (SHGR)
  • Snow pellets/Graupel (GS)
  • Ice crystals (IC)

The code in the brackets is the METAR code for each phenomenon.^[3] Drizzle is fairly steady, light precipitation. ... This article is about precipitation. ... Freezing drizzle is drizzle that freezes on contact with the ground or an object at or near the surface. ... Freezing Rain is a type of precipitation that begins as snow at higher altitude, falling from a cloud towards earth, melts completely on its way down while passing through a layer of air above freezing temperature, and then encounters a layer below freezing at lower level to become supercooled. ... For other uses, see Snow (disambiguation). ... It has been suggested that this article or section be merged with Graupel. ... Snow grains are a form of precipitation characterized as: white, opaque grains of ice very small <1 mm, fairly flat or enlongated, unlike Snow pellets they dont bounce or breakup on impact, very small amounts fall, mostly from Stratus or Fog, Never in the form of a shower. ... Sleet can refer to at least two different forms of precipitation. ... This article is about the precipitation. ... Graupel can be any of the following types of solid-ice precipitation: hail - large chunks of ice such as from a strong or severe thunderstorm sleet - small pellets of raindrops that have frozen in mid-air, in winter or a thunderstorm snow pellets - when freezing fog forms 2-5mm balls... Diamond dust is the name commonly used to refer to a ground-level cloud composed of tiny ice crystals. ... METAR (for METeorological Aerodrome Report) is a format for reporting weather information. ...

How air becomes saturated

Air contains moisture, measured in grams of water per kilogram of dry air (g/kg), but most commonly reported as a relative humidity percentage. How much moisture a parcel of air can hold before it becomes saturated (100% relative humidity) depends on its temperature. Warmer air has a higher capacity for holding moisture than cooler air. Because of this property of the air, one way to saturate a parcel of air is to cool it. The dew point is the temperature that a parcel needs to be cooled to for saturation to occur. A hygrometer used to measure the humidity of air. ... The dew point (or dewpoint) is the temperature which a given parcel of air must be cooled, at constant barometric pressure, for water vapor to condense into water. ...

Late-summer rainstorm in Denmark

Some cooling mechanisms include: Image File history File linksMetadata Download high resolution version (859x600, 362 KB) En: Rain near the village Lunde, The north of Funen, Denmark Da: Regnbyge ved Lunde på Nordfyn, Danmark Date: 6. ... Image File history File linksMetadata Download high resolution version (859x600, 362 KB) En: Rain near the village Lunde, The north of Funen, Denmark Da: Regnbyge ved Lunde på Nordfyn, Danmark Date: 6. ... Rain falling Rain on an umbrella Rain is a form of precipitation, as are snow, sleet, hail, and dew. ...

• Lift (convective, mechanical, positive vorticity advection)
  • Conductive cooling (warm air moves over a cool surface)
  • Radiational cooling (heat radiates off into space at night)
  • Evaporative cooling (air temperature falls as liquid water uses the energy to change phase to vapour)

The other way to saturate an air parcel is to add moisture to it, by:

• Precipitation falling from above (stratus forming in the rain under a higher cloud)
• Daytime heating evaporating water from the surface of oceans/lakes
• Drier air moving over open water (snow streamers off the Great Lakes in winter)

The Great Lakes from space The Laurentian Great Lakes are a group of five large lakes in North America on or near the Canada-United States border. ...

How precipitation forms

Condensation and coalescence are important parts of the water cycle

Download high resolution version (860x589, 761 KB)Water cycle http://ga. ... Download high resolution version (860x589, 761 KB)Water cycle http://ga. ... The movement of water around, over, and through the Earth is called the water cycle. ...

Condensation

Precipitation begins forming when warm, moist air rises. As the air cools, water vapor begins to condense on condensation nuclei, forming clouds. After the water droplets grow large enough, two processes can occur to form precipitation. Aerosol pollution over Northern India and Bangladesh - NASA Cloud condensation nuclei or CCNs (also known as cloud seeds) are small particles (typically 0. ... See also drop (telecommunication). ...

Coalescence

Coalescence occurs when water droplets fuse to create larger water droplets, or when water droplets freeze onto an ice crystal. Air resistance typically causes the water droplets in a cloud to remain stationary. When air turbulence occurs, water droplets collide, producing larger droplets. As these larger water droplets descend, coalescence continues, so that drops become heavy enough to overcome air resistance and fall as rain. Coalescence generally happens most often in clouds above freezing Look up coalescence in Wiktionary, the free dictionary. ...

Bergeron process

The Bergeron process occurs when ice crystals acquire water molecules from nearby supercooled water droplets. As these ice crystals gain enough mass, they begin to fall. This generally requires more mass than coalescence when occurring between the crystal and neighboring water droplets. This process is temperature dependent, as supercooled water droplets only exist in a cloud that is below freezing. In addition, because of the great temperature difference between cloud and ground level, these ice crystals may melt as they fall and become rain. The Bergeron Findeisen Process is the formation of precipitation in the cold clouds of the mid and upper latitudes by ice crystal growth. ... Supercooling is the process of chilling a liquid below its freezing point, without its becoming solid. ...

Ways of precipitation

Frontal activity

Stratiform or dynamic precipitation occurs as a consequence of slow (cm/s) ascent of air in synoptic systems, such as along cold fronts, and in advance of warm fronts. Similar ascent is seen around tropical cyclones outside of the eyewall, and in comma head precipitation patterns around mid-latitude cyclones.^[4] In meteorology, a weather front is a boundary between two air masses with differing characteristics (e. ... Illustration of a warm front A warm front is defined as the leading edge of a mass of warm air. ... Cyclone Catarina, a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004 Hurricane and Typhoon redirect here. ... Eye of the storm redirects here. ... A mid-latitude cyclone or extratropical cyclone is a weather phenomenon associated with atmospheric low pressure that takes place in the temperate region between the tropical and polar regions. ...

Convection

Convective precipitation

Convection rain or showery precipitation occurs from convective clouds, e.g., cumulonimbus or cumulus congestus. It falls as showers with rapidly changing intensity. Convective precipitation falls over a certain area for a relatively short time, as convective clouds have limited horizontal extent. Most precipitation in the tropics appears to be convective; however, it has been suggested that stratiform precipitation also occurs.^[4][5] Graupel and hail always indicate convection. In mid-latitudes, convective precipitation is associated with cold fronts (often behind the front), squall lines, and warm fronts with significant available moisture. Image File history File links Konvektionsregen. ... Image File history File links Konvektionsregen. ... Convection rain is a type of rain which occurs in areas that intensely heated. ... Cumulonimbus cloud in central Oklahoma. ... Cumulus congestus clouds are characteristic of unstable areas of the atmosphere which are undergoing convection. ... A noontime scene from the Philippines on a day when the Sun is almost directly overhead. ... Graupel can be any of the following types of solid-ice precipitation: hail - large chunks of ice such as from a strong or severe thunderstorm sleet - small pellets of raindrops that have frozen in mid-air, in winter or a thunderstorm snow pellets - when freezing fog forms 2-5mm balls... This article is about the precipitation. ... In meteorology, a weather front is a boundary between two air masses with differing characteristics (e. ... A squall or squall line is a line of thunderstorms with a common leading convection line, or mesocyclone, which tends to create a powerful gust front. ...

Orographic effects

Main article: Orographic lift

Orographic precipitation

Orographic precipitation occurs on the windward side of mountains and is caused by the rising air motion of a large-scale flow of moist air across the mountain ridge, resulting in adiabatic cooling and condensation. This wave cloud pattern formed off of the ÃŽle Amsterdam in the far southern Indian Ocean, due to orographic lift of an airmass by the island, producing alternating bands of condensed and invisible humidity downwind of the island as the moist air moves in vertical waves and the moisture successively... Image File history File links Steigungsregen. ... Image File history File links Steigungsregen. ... Windward is the side of a boat into which the wind is blowing. ... The adiabatic lapse rate is the rate of temperature change that occurs in an atmosphere as a function of elevation, assuming that air behaves adiabatically. ...

In mountainous parts of the world subjected to relatively consistent winds (for example, the trade winds), a more moist climate usually prevails on the windward side of a mountain than on the leeward (downwind) side. Moisture is removed by orographic lift, leaving drier air (see katabatic wind) on the descending (generally warming), leeward side where a rain shadow is observed. Image:Atmospheric circulatlion. ... Leeward is the side of a boat away from the direction where the wind is coming (i. ... A katabatic wind, from the Greek word katabatikos meaning going downhill, is a wind that blows down a topographic incline such as a hill, mountain, or glacier. ... For the Australian television series see Rain Shadow (TV series). ...

Orographic precipitation is well known on oceanic islands, such as the Hawaiian Islands, where much of the rainfall received on an island is on the windward side, and the leeward side tends to be quite dry, almost desert-like, by comparison. This phenomenon results in substantial local gradients of average rainfall, with coastal areas receiving on the order of 500 to 750 mm per year (20 to 30 inches), and interior uplands receiving over 2.5 m per year (100 inches). Leeward coastal areas are especially dry 500 mm per year (20 inches)at Waikiki), and the tops of moderately high uplands are especially wet – ~12 m per year (~475 inches) at Wai'ale'ale on Kaua'i). Map of the Hawaiian Islands, a chain of islands that stretches 2,400 km in a northwesterly direction from the southern tip of the Island of Hawaii. ... For other uses, see Phenomena (disambiguation). ... WaikÄ«kÄ« seen from the top of Diamond Head or LÄ“ahi. ... Kauai (Hawaiian IPA pron. ...

In South America, the Andes mountain range blocks most of the Atlantic moisture that arrives in that continent, resulting in a desert-like climate on the Pacific coast of Peru and northern Chile, since the cold Humboldt Current ensures that the air off the Pacific is dry as well. On the leeward side of the Andes is the Atacama Desert of Chile. It is also blocked from moisture by mountains to its west as well. Not coincidentially, it is the driest place on earth.^[6] The Sierra Nevada range creates the same effect in North America forming the Great Basin desert, Mojave Desert and Sonoran Desert. This article is about the mountain system in South America. ... The Atlantic Ocean, not including Arctic and Antarctic regions. ... ... Atacama Desert The Atacama Desert is a virtually rainless plateau in South America, extending 966 km (600 mi) between the Andes mountains and the Pacific Ocean. ... This article is about the mountain range in the Western United States. ... Drainage map showing the Great Basin in orange Various Definitions of the Great Basin (NPS) Wheeler Peak in Great Basin National Park, Nevada. ... For the indigenous American tribe, see Mohave. ... Map of the Mojave and Sonoran deserts. ...

Tropical activity

Tropical activity in general consists of large air masses several hundred miles across with low pressure at the centre and with winds blowing around the centre in either a clockwise direction (southern hemisphere) or counterclockwise (northern hemisphere). Precipitation arises when a warm front is formed by an advancing mass of warm air, which moves up an inclined surface of retreating cold air and is chilled in the process of being lifted up resulting in rainfall.

The Great Sandy Desert has nearly all its rain during from monsoonal thunderstorms or the occasional tropical cyclone rain depression. Thunderstorms occur on an average of 20–30 days annually through most of the area.^[7] Although the desert has fairly high precipitation rates, due to the high rates of evaporation, this area remains an arid environment with vast areas of sands. Location of deserts in Australia This article is about the Australian desert. ... Cyclone Catarina, a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004 Hurricane and Typhoon redirect here. ...

Other areas of the world which see these rare precipitation events in deserts are northwest Mexico, the southwestern United States, and southwest Asia. In North America, the Sonoran and Chihuahuan Deserts have received some tropical rainfall in the last 10 years. Tropical activity is rare in all deserts, but what rain does arrive there is important to the existence of the delicate ecosystem. Regional definitions vary from source to source. ... Map of the Mojave and Sonoran deserts. ... Map of the Chihuahuan Desert. ...

Rainfall characteristics

Size and shape

Raindrops have sizes ranging from 0.1 to up to approximately 9 mm mean diameter, above which they tend to break up. Smaller drops are called cloud droplets, and their shape is spherical. As a raindrop increases in size, its shape becomes more oblate, with its largest cross-section facing the oncoming airflow. Contrary to the cartoon pictures of raindrops, their shape does not resemble a teardrop.

Intensity and duration

These are usually inversely related, i.e., high intensity storms are likely to be of short duration and low intensity storms can have a long duration.

Intensity and area

We can expect a less intense rainfall over a large area than we can over a small area.

Intensity and drop size

High intensity storms have a larger drop size than low intensity storms.

Measurement of precipitation

See also: Rain gauge, Disdrometer, and Snow gauge

The standard way of measuring rainfall or snowfall is the standard rain gauge, which can be found in 4-inch/100 mm plastic and 8-inch/200 mm metal varieties.^[8] The inner cylinder is filled by 25 mm/1 inch of rain, with overflow flowing into the outer cylinder. Plastic gages will have markings on the inner cylinder down to 0.25 mm/0.01" resolution, which metal gages will require use of a stick designed with the appropriate 0.25 mm/0.01" markings. After the inner cylinder is filled, the amount inside it is discarded, then filled with the remaining rainfall in the outer cylinder until all the fluid in the outer cylinder is gone, adding to the overall total until the outer cylinder is empty. These gages are winterized by removing the funnel and inner cylinder and allowing the snow/freezing rain to collect inside the outer cylinder. Once the snowfall/ice is finished accumulating, or as you approach 300 mm/12", one can either bring it inside to melt, or use luke warm water to fill the inner cylinder with in order to melt the frozen precipitation in the outer cylinder, keeping track of the warm fluid added, which is subsequently subtracted from the overall total once all the ice/snow is melted. Standard Rain Gauge Tipping Bucket Rain Gauge Recorder Close up of a Tipping Bucket Rain Gauge Recorder chart A rain gauge (also known as an udometer or a pluviometer[fluviograph] or a cup) is a type of instrument used by meteorologists and hydrologists to gather and measure the amount of... A disdrometer is an instrument used to measure the drop size distribution and velocity of falling precipitation. ... Snow Gauge A snow gauge is a meteorological instrument used to record the depth of snowfall at a specific location. ...

Other types of gages include the popular wedge gage (the cheapest rain gage and most fragile), the tipping bucket rain gage,^[9] and the weighing rain gage.^[10] The wedge and tipping bucket gages will have problems with snow. Attempts to compensate for snow/ice by warming the tipping bucket meet with limited success, since snow may sublimate if the gage is kept much above freezing. Weighing gages with antifreeze should do fine with snow, but again, the funnel needs to be removed before the event begins. For those looking to measure rainfall the most inexpensively, a can that is cylindrical with straight sides will act as a rain gage if left out in the open, but its accuracy will depend on what ruler you use to measure the rain with. Any of the above rain gages can be made at home, with enough know-how.^[11]

Once someone has a device to measure precipitation, various networks exist across the United States and elsewhere where rainfall measurements can be submitted through the internet, such as CoCoRAHS^[12] or GLOBE.^[13] If a network is not available in the area where one lives, the nearest local weather office will likely be interested in the measurement.^[14] An important use of precipitation data is for forecasting of river flows and river water quality using hydrological transport models such as SWMM, SHE or the DSSAM Model. River in Madagascar relatively free of sediment load An hydrological transport model is a mathematical model used to simulate river or stream flow and calculate water quality parameters. ... The US Environment Protection Agency Storm Water Management Model (SWMM) is a dynamic rainfall-runoff simulation model used for single event or long-term (continuous) simulation of runoff quantity and quality from primarily urban areas. ... Lake Tahoe, headwater sub-basin of the Truckee River watershed The DSSAM Model (Dynamic Stream Simulation and Assessment. ...

Return period

The likelihood or probability of an event with a specified intensity and duration, is called the return period or frequency. The intensity of a storm can be predicted for any return period and storm duration, from charts based on historic data for the location. A return period also known as a recurrence interval is an estimate of the liklihood of a flood or river discharge flow of a certain size. ...

Frequency of flooding

There is no way of telling when the next flood will arrive or how big it will be, but past flooding events can help provide some information as to what to expect.

1 in 10 year storm

The term “1 in 10 year storm” describes a rainfall event which is rare and is only likely to occur once every 10 years, so it has a 10% likelihood any given year. The amount of rain which will fall will be greater and cause the flooding to be worse than for a 1 in 1 year event.

1 in 100 year storm

The term “1 in 100 year storm” (see also 100-year flood) describes a rainfall event which is extremely rare and which will occur with a likelihood of only once in a century, so has a 1% likelihood in any given year. The amount of rain which will fall will be extreme and cause far greater flooding to be worse than for a 1 in 1 year event. A one-hundred year flood is calculated to be the maximum level of flood water expected to occur on average once every one hundred years. ...

As with all “probability” events, it is still possible to have two “1 in 100 Year Storms” in the same year.

See also

• Monsoon
• Steam
• Umbrella
• Rainfall patterns in the United States
• List of meteorology topics

For other uses, see Monsoon (disambiguation). ... For other uses, see Steam (disambiguation). ... An umbrella or parasol (sometimes colloquially, gamp, brolly, or bumbershoot) is a canopy designed to protect against precipitation or sunlight. ... // Major elements are prevailing westerly winds and ocean currents moving toward the equator. ... This page has a list of meteorology topics. ...

References

Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 331st day of the year (332nd in leap years) in the Gregorian calendar. ... ISSN, or International Standard Serial Number, is the unique eight-digit number applied to a periodical publication including electronic serials. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 331st day of the year (332nd in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 330th day of the year (331st in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 332nd day of the year (333rd in leap years) in the Gregorian calendar. ...

External links

• Collision/Coalescence; The Bergeron Process
• Report your local rainfall inside the United States at this site (CoCoRaHS)
• Report your local rainfall related to tropical cyclones worldwide at this site
• Global Precipitation Climatology Center GPCC
• Falling Rain Genomics
• Types of rainfall (BBC)