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Precipitation (meteorology)

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Precipitation (meteorology)



 
 
In meteorology
Meteorology

Meteorology is the interdisciplinary scientific study of the Earth's atmosphere that focuses on weather processes and forecasting . Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the eighteenth century....
, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena) is any product of the condensation of atmospheric
Atmosphere

An atmosphere is a layer of gases that may surround a material body of sufficient mass, by the gravity of the body, and are retained for a longer duration if gravity is high and the atmosphere's temperature is low....
 water vapour
Water vapor

Water vapor or water vapour , also aqueous vapor, is the gas phase of water . Water vapor is one Phase of the water cycle within the hydrosphere....
 that is deposited on the earth's surface. It occurs when the atmosphere, a large gaseous solution
Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
, becomes saturated with water vapour and the water condenses and falls out of solution (i.e., precipitates
Precipitation (chemistry)

Precipitation is the formation of a solid in a solution during a chemical reaction. When the reaction occurs, the solid formed is called the precipitate, and the liquid remaining above the solid is called the supernate....
). Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapour to the air.






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In meteorology
Meteorology

Meteorology is the interdisciplinary scientific study of the Earth's atmosphere that focuses on weather processes and forecasting . Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the eighteenth century....
, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena) is any product of the condensation of atmospheric
Atmosphere

An atmosphere is a layer of gases that may surround a material body of sufficient mass, by the gravity of the body, and are retained for a longer duration if gravity is high and the atmosphere's temperature is low....
 water vapour
Water vapor

Water vapor or water vapour , also aqueous vapor, is the gas phase of water . Water vapor is one Phase of the water cycle within the hydrosphere....
 that is deposited on the earth's surface. It occurs when the atmosphere, a large gaseous solution
Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
, becomes saturated with water vapour and the water condenses and falls out of solution (i.e., precipitates
Precipitation (chemistry)

Precipitation is the formation of a solid in a solution during a chemical reaction. When the reaction occurs, the solid formed is called the precipitate, and the liquid remaining above the solid is called the supernate....
). Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapour to the air. Virga
Virga

In meteorology, virga is an observable streak or shaft of precipitation that falls from a cloud but evaporates before reaching the ground. At high altitudes the precipitation falls mainly as ice crystals before melting and finally evaporating; this is usually due to compressional heating, because the atmospheric pressure increases closer...
 is precipitation that begins falling to the earth but evaporates before reaching the surface; it is one of the ways air can become saturated. Precipitation forms via collision with other rain drops or ice crystals within a cloud
Cloud

A cloud is a visible mass of Drop or frozen crystals floating in the Celestial body atmosphere above the surface of the Earth or another planetary body....
.

Rain drops range in size from oblate, pancake-like shapes for larger drops, to small spheres for smaller drops. Rain drops are not shaped like tear drops, but rather like flattened pancakes. Precipitation that reaches the surface of the earth can occur in many different forms, including rain
Rain

Rain is liquid precipitation . On Earth, it is the condensation of atmospheric water vapor into droplet heavy enough to fall, often making it to the surface....
, freezing rain
Freezing rain

Freezing rain is a type of precipitation associated with a temperature inversion airmass in cold climates. It is described as 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 be...
, drizzle
Drizzle

Drizzle is light precipitation consisting of liquid water drops smaller than those of rain, and generally smaller than 0.5 mm in diameter. Drizzle is normally produced by low Stratus cloud clouds and Stratocumulus_cloud clouds....
, ice needles
Diamond dust

Diamond dust is a ground-level cloud composed of tiny ice crystals. This List of meteorological phenomena is also referred to simply as ice crystals and is reported in the METAR code as IC....
, snow
Snow

Snow is a type of precipitation in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. The process of this precipitation is called snowfall....
, ice pellets
Ice pellets

Ice pellets are a form of precipitation consisting of small, translucent ice balls. This form of precipitation is also known as sleet in the United States....
 or sleet, graupel and hail
Hail

Hail is a form of Precipitation which consists of balls or irregular lumps of ice . Hailstones on Earth usually consist mostly of ice and measure between 5 and 150 millimeters in diameter, with the larger stones coming from severe thunderstorms....
. While snow and ice pellets require temperatures to be near or below freezing, hail can occur during much warmer temperature regimes due to the process of its formation. Precipitation may occur on other celestial bodies, e.g. when it gets cold, Mars
MARS

In cryptography, MARS is a block cipher that was IBM's submission to the Advanced Encryption Standard process. MARS was selected as an AES finalist in August 1999, after the AES2 conference in March 1999, where it was voted as the fifth and last finalist algorithm....
 has precipitation which most likely takes the form of ice needles, rather than rain or snow.

Moisture overriding weather fronts is a major method of precipitation production. If enough moisture and upward motion is present, precipitation falls from convective clouds such as cumulonimbus and organize into narrow rainbands. Precipitation can also form due to forced ascent up the windward side of a mountain or mountain range. On the leeward side of mountains, desert climates can exist due to the dry air caused by compressional heating. The movement of the monsoon trough
Monsoon trough

The monsoon trough, also known as the Intertropical Convergence Zone , is depicted by a line on a weather map showing the locations of minimum sea level pressure within the monsoon region, and is a convergence zone between the wind patterns of the southern and northern hemispheres....
, or Intertropical convergence zone
Intertropical Convergence Zone

The 'Intertropical Convergence Zone' , also known as the 'Intertropical Front', 'Monsoon trough', or the 'Equatorial Convergence Zone', is a belt of low pressure area girdling Earth at the equator....
, brings rainy seasons
Wet season

Rainy season is the time of year, covering one or more months, when most of the average annual rainfall in a region falls. The term green season is also sometimes used as a euphemism by tourist authorities....
 to savannah
Savannah

Savannah or savanna is a type of grassland.It can also mean:...
 clime
Clime

The seven climes was a notion of dividing the Earth into zones in Classical Antiquity.The lists of klimata found in early geographers vary in their extension, but by convention, they numbered seven, counted from south to north....
s. Precipitation is a major component of the water cycle
Water cycle

The water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth....
, and is responsible for depositing most of the fresh water
Fresh Water

Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve....
 on the planet
Planet

A planet , as 2006 definition of planet by the International Astronomical Union , is a celestial body orbiting a star or Stellar evolution#Stellar remnants that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared the neighbourhood of planetesimals....
. Approximately 505,000 km3 (121,000 cu mi) of water falls as precipitation each year, 398,000 km3 (95,000 cu mi) of it over the ocean
Ocean

An ocean is a major body of Seawater, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a World Ocean that is customarily divided into several principal oceans and smaller seas....
s. Given the Earth
Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
's surface area, that means the globally-averaged annual precipitation is about , and the average annual precipitation over oceans is about .

Types


Precipitation is a major component of the water cycle
Water cycle

The water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth....
, and is responsible for depositing most of the fresh water
Fresh Water

Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve....
 on the planet
Planet

A planet , as 2006 definition of planet by the International Astronomical Union , is a celestial body orbiting a star or Stellar evolution#Stellar remnants that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared the neighbourhood of planetesimals....
. Approximately 505,000 km3 (121,000 cu mi) of water falls as precipitation each year, 398,000 km3 (95,000 cu mi) of it over the ocean
Ocean

An ocean is a major body of Seawater, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a World Ocean that is customarily divided into several principal oceans and smaller seas....
s. Given the Earth
Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
's surface area, that means the globally-averaged annual precipitation is about 1 m (39 in), and the average annual precipitation over oceans is about 1.1 m (43 in). 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.

How air becomes saturated


Cooling air to its dew point

Regnbyge
Air contains water vapour, measured in grams of water per kilogram of dry air (g/kg), but most commonly reported as a relative humidity
Relative humidity

Relative humidity is a term used to describe the amount of water vapor that exists in a gaseous mixture of air and water....
. How much water vapour a parcel of air can contain before it becomes saturated (100% relative humidity) depends on its temperature. Warmer air can contain more water vapour than cooler air before becoming saturated. Therefore, one way to saturate a parcel of air is to cool it. The dew point
Dew point

The dew point is the temperature to which a given parcel of air must be cooled, at constant barometric pressure, for water vapor to Condensation into water....
 is the temperature to which a parcel must be cooled in order to become saturated. Water vapor normally begins to condense on condensation nuclei
Cloud condensation nuclei

Cloud condensation nuclei or CCNs are small particles about which cloud droplets coalescence . Water requires a non-gaseous surface to make the transition from a vapour to a liquid....
 such as dust, ice, and salt in order to form clouds. An elevated portion of a frontal zone forces broad areas of lift, which form clouds decks such as altostratus or cirrostratus. Stratus
Stratus cloud

Stratus means layer or blanket in Latin. A stratus cloud is a cloud belonging to a class characterized by horizontal layering with a uniform base, as opposed to convective clouds that are as tall or taller than wide ....
 is a stable cloud deck which tends to form when a cool, stable air mass is trapped underneath a warm air mass. It can also form due to the lifting of advection fog during breezy conditions.

There are four main mechanisms for cooling the air to its dew point: adiabatic cooling, conductive cooling, radiational cooling, and evaporative cooling. Adiabatic cooling occurs when air rises and expands. The air can rise due to convection
Convection

Convection in the most general terms refers to the movement of molecules within fluids . Convection is one of the major modes of heat transfer and mass transfer....
, large-scale atmospheric motions, or a physical barrier such as a mountain (orographic lift
Orographic lift

Orographic lift occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain. As the air mass gains altitude it expands and cools Adiabatic cooling....
). Conductive cooling occurs when the air comes into contact with a colder surface, usually by being blown from one surface to another, for example from a liquid water surface to colder land. Radiational cooling occurs due to the emission of infrared radiation
Thermal radiation

Thermal radiation is electromagnetic radiation emitted from the surface of an object which is due to the object's temperature. Infrared radiation from a common household radiator or electric heater is an example of thermal radiation, as is the light emitted by a glowing incandescent light bulb....
, either by the air or by the surface underneath. Evaporative cooling occurs when moisture is added to the air through evaporation, which forces the air temperature to cool to its wet bulb temperature, or until it reaches saturation.

Adding moisture to the air

The main ways water vapour is added to the air are:

  • Wind convergence into areas of upward motion
  • Precipitation or virga falling from above
  • Daytime heating evaporating water from the surface of oceans, water bodies or wet land
  • Transpiration from plants
  • Cool, dry air moving over warmer water
  • Lifting air over mountains


Formation

Water Cycle

Coalescence and the Bergeron process

Coalescence
Coalescence (meteorology)

Coalescence is the process by which two or more droplets or particles merge during contact to form a single daughter droplet . It can take place in many processes, ranging from meteorology to astrophysics....
 occurs when water droplets fuse to create larger water droplets, or when water droplets freeze onto an ice crystal, which is known as the Bergeron process
Bergeron process

The Bergeron Findeisen Process , also known as the cold rain or ice crystal process, is the formation of Precipitation in the cold clouds of the mid and upper latitudes by ice crystal growth....
. 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. In clouds below freezing, when 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.

Raindrop characteristics

Raindrops have sizes ranging from to 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 of rainfall 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. Rain drops associated with melting hail tend to be larger than other rain drops.

Causes


Frontal activity

Stratiform or dynamic precipitation occurs as a consequence of slow ascent of air in synoptic systems (on the order of cm/s), such as over surface cold front
Cold front

A cold front is defined as the leading edge of a cooler and drier mass of air, replacing a warmer mass of air.Development of cold front...
s, and over and ahead of warm front
Warm front

A warm front is defined as the leading edge of an advancing Air mass of warm air; it separates warm air from the colder air ahead....
s. Similar ascent is seen around tropical cyclone
Tropical cyclone

A tropical cyclone is a storm characterized by a large low pressure system center and numerous thunderstorms that produce strong winds and flooding rain....
s outside of the eyewall
Eye (cyclone)

The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30?65 km in diameter....
, and in comma head precipitation patterns around mid-latitude cyclone
Mid-latitude cyclone

Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere . Cyclogenesis is an umbrella term for several different processes, all of which result in the development of some sort of cyclone....
s. A wide variety of weather can be found along 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. Precipitation may occur on other celestial bodies other than Earth. When it gets cold, Mars
MARS

In cryptography, MARS is a block cipher that was IBM's submission to the Advanced Encryption Standard process. MARS was selected as an AES finalist in August 1999, after the AES2 conference in March 1999, where it was voted as the fifth and last finalist algorithm....
 has precipitation which most likely takes the form of ice needles, rather than rain or snow.

Convection


Konvektionsregen
Convective 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
Tropics

The Tropics, seated in the equatorial regions of the world, are limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately 23?26' N latitude, and the Tropic of Capricorn in the southern hemisphere at 23?26' S latitude....
 appears to be convective; however, it has been suggested that stratiform precipitation also occurs. Graupel and hail
Hail

Hail is a form of Precipitation which consists of balls or irregular lumps of ice . Hailstones on Earth usually consist mostly of ice and measure between 5 and 150 millimeters in diameter, with the larger stones coming from severe thunderstorms....
 indicate convection. In mid-latitudes, convective precipitation in intermittent and often associated with baroclinic boundaries such as cold front
Cold front

A cold front is defined as the leading edge of a cooler and drier mass of air, replacing a warmer mass of air.Development of cold front...
s, squall line
Squall line

A squall line is a line of thunderstorms#Severe_thunderstorm that can form along and/or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front....
s, and warm fronts.

Orographic effects


Steigungsregen
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. In mountainous parts of the world subjected to relatively consistent winds (for example, the trade wind
Trade wind

The trade winds are the Prevailing winds of easterlies surface winds found in the tropics near the Earth's equator. The trade winds blow predominantly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere....
s), a more moist climate
Climate

Climate encompasses the temperatures, humidity, atmospheric pressure, winds, rainfall, atmospheric particle count and numerous other Meteorology elements in a given region over long periods of time, as opposed to the term weather, which refers to current activity of these same elements....
 usually prevails on the windward side of a mountain than on the leeward or downwind side. Moisture is removed by orographic lift, leaving drier air (see katabatic wind
Katabatic wind

File:Katabatic-wind hg.pngFile:Antarctic shelf ice hg.pngFile:Vent catabatique - Catabatic Wind.jpgFile:Sea ice by fruchtzwerg's world.jpgA katabatic wind, from the Greek language word katabatic meaning "going downhill", is the technical name for a drainage wind, a wind that carries high density air from a higher elevation down a slo...
) on the descending and generally warming, leeward side where a rain shadow
Rain shadow

For the Australian television series see Rain Shadow .A rain shadow or rainshadow, or more accurately, precipitation shadow, is a dry region of land that is leeward of a mountain range or other geographic feature, with respect to prevailing wind direction....
 is observed.

In Hawaii
Hawaii

File:Pahoehoe and Aa flows at Hawaii.jpgThe State of Hawaii is a U.S. state in the United States, located on an archipelago in the central Pacific Ocean southwest of the continental United States, southeast of Japan, and northeast of Australia....
, Mount Wai?ale?ale, on the island of Kauai, is notable for its extreme rainfall, as it has the second highest average annual rainfall on Earth, with . Storm systems affect the state with heavy rains between October and March. Local climates vary considerably on each island due to their topography, divisible into windward (Koolau) and leeward (Kona) regions based upon location relative to the higher mountains. Windward sides face the east to northeast trade winds and receive much more rainfall; leeward sides are drier and sunnier, with less rain and less cloud cover.

In South America, the Andes
Andes

The Andes form the world's longest exposed mountain range. They lie as a continuous chain of highland along the western coast of South America. The range is over 7,000 km long, 200-700 km wide , and of an average height of about 4,000 m ....
 mountain range blocks Pacific
Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. Its name is derived from the Latin name Mare Pacificum, "peaceful sea", bestowed upon it by the Portugal explorer Ferdinand Magellan....
 moisture that arrives in that continent, resulting in a desertlike climate just downwind across western Argentina. The Sierra Nevada range creates the same effect in North America forming the Great Basin
Great Basin

The Great Basin is a large, arid region of the western United States. Its boundaries depend on how it is defined. Its most common definition is the contiguous drainage basin, roughly between the Wasatch Mountains, in Utah and the Sierra Nevada , that has no natural outlet to the sea....
 and Mojave Desert
Mojave Desert

The Mojave Desert , , locally referred to as the High Desert, occupies a significant portion of southeastern California and smaller parts of central California, southern Nevada, and northwestern Arizona, in the United States....
s.

Within the tropics

The wet, or rainy, season is the time of year, covering one or more months, when most of the average annual rainfall in a region falls. The term green season is also sometimes used as a euphemism
Euphemism

A euphemism is a substitution of an agreeable or less offensive expression in place of one that may offend or suggest something unpleasant to the listener, or in the case of #Doublespeak, to make it less troublesome for the speaker....
 by tourist authorities. Areas with wet seasons are dispersed across portions of the tropics
Tropics

The Tropics, seated in the equatorial regions of the world, are limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately 23?26' N latitude, and the Tropic of Capricorn in the southern hemisphere at 23?26' S latitude....
 and subtropics
Subtropics

For information on the American literary journal, see Subtropics The subtropics are the Geographical zone of the Earth immediately north and south of the tropics zone, which is bounded by the Tropic of Cancer and the Tropic of Capricorn, at latitude 23.5? north and south....
. Savanna
Savanna

A savanna, or savannah, is a tropical, subtropical or temperate woodland ecosystem characterized by the trees being sufficiently small or widely spaced so that the Canopy does not close....
 climates and areas with monsoon
Monsoon

A monsoon is a seasonal prevailing wind that lasts for several months. The term was first used in English in India, Bangladesh, Pakistan, and neighboring countries to refer to the big seasonal winds blowing from the Indian Ocean and Arabian Sea in the southwest bringing heavy rainfall to the region....
 regimes have wet summers and dry winters. Tropical rainforests technically do not have dry or wet seasons, since their rainfall is equally distributed through the year. Some areas with pronounced rainy seasons will see a break in rainfall mid-season when the intertropical convergence zone
Intertropical Convergence Zone

The 'Intertropical Convergence Zone' , also known as the 'Intertropical Front', 'Monsoon trough', or the 'Equatorial Convergence Zone', is a belt of low pressure area girdling Earth at the equator....
 or monsoon trough
Monsoon trough

The monsoon trough, also known as the Intertropical Convergence Zone , is depicted by a line on a weather map showing the locations of minimum sea level pressure within the monsoon region, and is a convergence zone between the wind patterns of the southern and northern hemispheres....
 move poleward of their location during the middle of the warm season. When the wet season occurs during the warm season, or summer
Summer

Summer generally refers to the warmest and most humid season between spring and autumn, from the summer solstice to the autumnal equinox. In the Northern Hemisphere, this falls from the June solstice to the September equinox, while in the Southern Hemisphere it falls from the December solstice to the March equinox....
, rain falls mainly during the late afternoon and early evening hours. The wet season is a time when air quality improves, freshwater quality improves, and vegetation grows significantly. Soil
Soil

Soil is the naturally occurring, unconsolidated or loose covering on the Earth's surface. Soil is composed of particles of broken rock that have been altered by chemical and environmental processes including weathering and erosion....
 nutrients diminish and erosion increases. Animals have adaptation and survival strategies for the wetter regime. Unfortunately, the previous dry season leads to food shortages into the wet season, as the crops have yet to mature. Developing countries have noted that their populations show seasonal weight fluctuations due to food shortages seen before the first harvest, which occurs late in the wet season.

Tropical cyclones, a source of very heavy rainfall, consist of large air masses several hundred miles across with low pressure at the centre and with winds blowing inward towards the centre in either a clockwise direction (southern hemisphere) or counterclockwise (northern hemisphere). Although cyclone
Cyclone

In meteorology, a cyclone refers to an area of closed, circular fluid motion rotating in the same direction as the Earth's rotation. This is usually characterized by inward spiraling winds that rotate counter clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth....
s can take an enormous toll in lives and personal property, they may be important factors in the precipitation regimes of places they impact, as they may bring much-needed precipitation to otherwise dry regions. Areas in their path can receive a year's worth of rainfall from a tropical cyclone passage.

Measurement of precipitation



The standard way of measuring rainfall or snowfall is the standard rain gauge, which can be found in 100-mm (4-in) plastic and 200-mm (8-in) metal varieties. The inner cylinder is filled by 25 mm (1 in) 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 in) resolution, which metal gages will require use of a stick designed with the appropriate 0.25 mm (0.01 in) 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. Some add anti-freeze to their gage so they do not have to melt the snow or ice that falls into the gage. Once the snowfall/ice is finished accumulating, or as you approach 300 mm (12 in), 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.

Other types of gages include the popular wedge gage (the cheapest rain gage and most fragile), the tipping bucket rain gage, and the weighing rain gage. 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.

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 or GLOBE. If a network is not available in the area where one lives, the nearest local weather office will likely be interested in the measurement.

Return period

The likelihood or probability of an event with a specified intensity and duration, is called the return period
Return period

A return period also known as a recurrence interval is an estimate of the interval of time between events like an earthquake, flood or discharge of a certain intensity or size....
 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. 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 rain fall will be greater and the flooding will be worse than the worst storm one would expect in any single year. The term 1 in 100 year storm 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 rain fall will be extreme and flooding to be worse than a 1 in 10 year event. As with all probability events, it is possible to have multiple "1 in 100 Year Storms" in a single year.

Forecasting

The Quantitative Precipitation Forecast (abbreviated QPF) is the expected amount of liquid precipitation accumulated over a specified time period over a specified area. A QPF will be specified when a measurable precipitation type reaching a minimum threshold is forecast for any hour during a QPF valid period. Precipitation forecasts tend to be bound by synoptic hours such as 0000, 0600, 1200 and 1800 GMT. Terrain is considered in QPFs by use of topography or based upon climatological precipitation patterns from observations with fine detail. Starting in the mid to late 1990's, QPFs were used within hydrologic forecast models to simulate impact to rivers throughout the United States. Forecast models
Numerical weather prediction

Numerical weather prediction uses current weather conditions as input into mathematical models of the atmosphere to weather forecasting. While the first efforts to accomplish this were done in the 1920's, it wasn't until the advent of the computer that it was feasible to do in real-time....
 show significant sensitivity to humidity levels within the planetary boundary layer
Planetary boundary layer

The planetary boundary layer , also known as the atmospheric boundary layer , is the lowest part of the atmosphere and its behavior is directly influenced by its contact with a planetary surface....
, or in the lowest levels of the atmosphere, which decreases with height. QPF can be generated on a quantitative, forecasting amounts, or a qualitative, forecasting the probability of a specific amount, basis. Radar imagery forecasting techniques show higher skill
Forecast skill

Skill in Forecasting or is a scaled representation of forecast error that relates the forecast accuracy of a particular forecast model to some reference model....
 than model forecasts within 6 to 7 hours of the time of the radar image. The forecasts can be verified through use of rain gage measurements, weather radar
Weather radar

A weather radar is a type of radar used to locate precipitation , calculate its motion, estimate its type , and weather forecasting its future position and intensity....
 estimates, or a combination of both. Various skill scores can be determined to measure the value of the rainfall forecast.

See also


  • List of meteorology topics
    List of meteorology topics

    This is a list of meteorology topics. The terms relate to meteorology, the interdisciplinary scientific study of the Earth's atmosphere that focuses on weather processes and forecasting....
  • Mango showers
    Mango showers

    Mango showers are the pre-monsoon showers in the India states of Karnataka and Kerala that help in the ripening of mangoes. Also known as April rains or Summer showers, they are a result of Thunderstorm over the Bay of Bengal ....
    , pre-monsoon
    Monsoon

    A monsoon is a seasonal prevailing wind that lasts for several months. The term was first used in English in India, Bangladesh, Pakistan, and neighboring countries to refer to the big seasonal winds blowing from the Indian Ocean and Arabian Sea in the southwest bringing heavy rainfall to the region....
     showers in the Indian
    India

    India, officially the Republic of India , is a country in South Asia. It is the List of countries and outlying territories by total area country by geographical area, the List of countries by population country, and the most populous liberal democracy in the world....
     states of Karnataka
    Karnataka

    Karnataka is a States and territories of India in the southern part of India. It was Unification of Karnataka on November 1, 1956, with the passing of the States Reorganisation Act....
     and Kerala
    Kerala

    Kerala is a Indian Union States and territories of India located in the southwestern part of India. With an Arabian Sea coastline on the west, it is bordered on the north by Karnataka and by Tamil Nadu on the south and east....
     that help in the ripening of mangoes.
  • Steam
    Steam

    In physical chemistry, and in engineering, steam refers to vaporized water. It is a pure, completely invisible gaseous phase . At standard temperature and pressure, pure steam occupies about 1,600 times the volume of an equal mass of liquid water....
  • Sunshower
    Sunshower

    A sunshower is an unusual meteorological phenomenon in which rain falls while the sun is shining . These conditions often lead to the appearance of a rainbow, if the sun is at a low enough angle ....
    , an unusual meteorological phenomenon
    Meteorological phenomenon

    A meteorological phenomenon is a weather phenomenon which can be explained by the principles of meteorology.* Air mass* Anticyclone* Arctic cyclone...
     in which rain
    Rain

    Rain is liquid precipitation . On Earth, it is the condensation of atmospheric water vapor into droplet heavy enough to fall, often making it to the surface....
     falls while the sun is shining.
  • Umbrella
    Umbrella

    An umbrella or parasol is a canopy designed to protect against precipitation or sunlight. The term parasol usually refers to an item designed to protect from the sun, and umbrella refers to a device more suited to protect from rain....
  • United States rainfall climatology
    United States rainfall climatology

    The characteristics of United States rainfall climatology differ significantly across the United States and its possessions. Late summer and fall extratropical cyclones bring a majority of the precipitation which falls across western, southern, and southeast Alaska annually....
  • Wintry showers, an informal meteorological
    Meteorology

    Meteorology is the interdisciplinary scientific study of the Earth's atmosphere that focuses on weather processes and forecasting . Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the eighteenth century....
     term for various mixtures of rain
    Rain

    Rain is liquid precipitation . On Earth, it is the condensation of atmospheric water vapor into droplet heavy enough to fall, often making it to the surface....
    , freezing rain
    Freezing rain

    Freezing rain is a type of precipitation associated with a temperature inversion airmass in cold climates. It is described as 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 be...
    , sleet
    Sleet

    Sleet may refer to:*Rain and snow mixed, particularly in countries where British English is spoken*Ice pellets, mainly within the United States...
     and snow
    Snow

    Snow is a type of precipitation in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. The process of this precipitation is called snowfall....
    .


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