it rains because the water droplets in the clouds increase too much and the water becomes too heavy...

8/2/2019 It Rains Because the Water Droplets in the Clouds Increase Too Much and the Water Becomes Too Heavy for the Cl

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it rains because the water droplets in the clouds increase too much and the water becomes too heavy for the

clouds and it falls out. the temperature must be over 31 degrees fernheight (i dont care if it is spelled wrong)for rain.

nmeteorology,precipitation (also known as one of the classes ofhydrometeors, which are atmosphericwater phenomena) is any product of the condensation ofatmosphericwater vaporthat falls under gravity.

[1]

The main forms of precipitation includedrizzle,rain,sleet,snow,graupelandhail. It occurs when a localportion of the atmosphere becomes saturated with water vapour and the water condenses.[2]Two processes,

possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapour to the air.

Generally, precipitation will fall to the surface; an exception isVirgawhich evaporates before reaching thesurface. Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals

within acloud. Rain drops range in size from oblate, pancake-like shapes for larger drops, to small spheres

for smaller drops. Unlike raindrops, snowflakes grow in a variety of different shapes and patterns,determined by thetemperatureandhumiditycharacteristics of the air the snowflake moves through on its

way to the ground. While snow and ice pellets require temperatures close to the ground to be near or below

freezing, hail can occur during much warmer temperature regimes due to the process of its formation.

Moisture overriding associated withweather frontsis an overall major method of precipitation production. Ifenough moisture and upward motion is present, precipitation falls from convective clouds such ascumulonimbusand can organize into narrowrainbands. Where relatively warm water bodies are present, for

example due to water evaporation from lakes,lake-effect snowfallbecomes a concern downwind of the

warm lakes within the coldcyclonicflow around the backside ofextratropical cyclones. Lake-effect snowfall

can be locally heavy.Thundersnowis possible within a cyclone'scomma headand within lake effectprecipitation bands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized

withinwindwardsides of the terrain at elevation. On the leeward side of mountains, desert climates can exist

due to the dry air caused by compressional heating. The movement of themonsoon trough, orintertropicalconvergence zone, bringsrainy seasonstosavannahclimes.

Precipitation is a major component of thewater cycle, and is responsible for depositing thefresh wateron theplanet. Approximately 505,000 cubic kilometres (121,000 cu mi) of water falls as precipitation each year;

398,000 cubic kilometres (95,000 cu mi) of it over theoceans.[3]

Given theEarth's surface area, that means

the globally averaged annual precipitation is 990 millimetres (39 in).Climateclassification systems such astheKppen climate classificationsystem use average annual rainfall to help differentiate between differing

climate regimes. Theurban heat islandeffect may lead to increased rainfall, both in amounts and intensity,

downwind of cities.Global warmingis also causing changes in the precipitation pattern globally.

Precipitation may occur on other celestial bodies, e.g. when it gets cold,Marshas precipitation which mostlikely takes the form of ice needles, rather than rain or snow.

Causes

[edit] Frontal activity

Main article:Weather fronts

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 surfacecold fronts, and over and ahead ofwarm fronts. Similar ascent is seenaroundtropical cyclonesoutside of theeyewall, and in comma-head precipitation patterns aroundmid-

latitude cyclones.[43]

A wide variety of weather can be found along an occluded front, with thunderstorms
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possible, but usually their passage is associated with a drying of the air mass. Occluded fronts usually form

around mature low-pressure areas.[44]

Precipitation may occur on celestial bodies other than Earth. When itgets cold,Marshas precipitation that most likely takes the form of ice needles, rather than rain or snow .[4]

[edit] Convection

Convective precipitation

Convective rain, or showery precipitation, occurs from convective clouds, e.g.,cumulonimbusorcumulus

congestus. It falls as showers with rapidly changing intensity. Convective precipitation falls over a certainarea for a relatively short time, as convective clouds have limited horizontal extent. Most precipitation in the

tropicsappears to be convective; however, it has been suggested that stratiform precipitation also

occurs.[25][43]

Graupelandhailindicate convection.[45]

In mid-latitudes, convective precipitation isintermittent and often associated with baroclinic boundaries such ascold fronts,squall lines, and warm

fronts.[46]

[edit] Orographic effects

See also:Orographic liftandPrecipitation types

Orographic precipitation

Orographic precipitation occurs on thewindwardside of mountains and is caused by the rising air motion ofa large-scale flow of moist air across the mountain ridge, resulting inadiabaticcooling and condensation. In

mountainous parts of the world subjected to relatively consistent winds (for example, thetrade winds), amore moistclimateusually prevails on the windward side of a mountain than on theleewardor downwind

side. Moisture is removed by orographic lift, leaving drier air (seekatabatic wind) on the descending and

generally warming, leeward side where arain shadowis observed.[21]

InHawaii,Mount Waialeale, on the island of Kauai, is notable for its extreme rainfall, as it has the secondhighest average annual rainfall on Earth, with 460 inches (12,000 mm).[47]Storm systems affect the state with

heavy rains between October and March. Local climates vary considerably on each island due to their
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topography, divisible into windward (Koolau) and leeward (Kona) regions based upon location relative to

the higher mountains. Windward sides face the east to northeasttrade windsand receive much more rainfall;leeward sides are drier and sunnier, with less rain and less cloud cover .[48]

In South America, theAndesmountain range blocks Pacific moisture that arrives in that continent, resultingin a desertlike climate just downwind across western Argentina.[49]TheSierra Nevadarange creates the same

effect in North America forming theGreat BasinandMojave Deserts.[50][51]

[edit] Snow

Main article:Snow

Lake-effect snow bands near theKorean Peninsula

Extratropical cyclonescan bring cold and dangerous conditions with heavy rain and snow with windsexceeding 119 km/h (74 mph),[52](sometimes referred to aswindstormsin Europe). The band of precipitation

that is associated with theirwarm frontis often extensive, forced by weak upward vertical motion of air over

the frontal boundary whichcondensesas it cools and produces precipitation within an elongated band,[53]

which is wide andstratiform, meaning falling out ofnimbostratusclouds.[54]When moist air tries to dislodge

an arctic air mass, overrunning snow can result within the poleward side of the elongated precipitation band.

In theNorthern Hemisphere, poleward is towards theNorth Pole, or north. Within theSouthern Hemisphere,poleward is towards theSouth Pole, or south.

Southwest of extratropical cyclones, curved cyclonic flow bringing cold air across the relatively warm waterbodies can lead to narrowlake-effect snowbands. Those bands bring strong localized snowfall which can be

understood as follows: Large water bodies such as lakes efficiently store heat that results in significant

temperature differences (larger than 13 C or 23 F) between the water surface and the air above .[55]

Because

of this temperature difference, warmth and moisture are transported upward, condensing into verticallyoriented clouds (see satellite picture) which produce snow showers. The temperature decrease with height

and cloud depth are directly affected by both the water temperature and the large-scale environment. The

stronger the temperature decrease with height, the deeper the clouds get, and the greater the precipitation rate

becomes.

[56]

In mountainous areas, heavy snowfall accumulates when air is forced to ascend the mountains and squeezeout precipitation along their windward slopes, which in cold conditions, falls in the form of snow. Because of

the ruggedness of terrain, forecasting the location of heavy snowfall remains a significant challenge.[57]

[edit] Within the tropics
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orea.jpghttp://en.wikipedia.org/wiki/File:Snow_Clouds_in_Korea.jpghttp://en.wikipedia.org/w/index.php?title=Precipitation_%28meteorology%29&action=edit&section=17http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-56http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-55http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-54http://en.wikipedia.org/wiki/Lake-effect_snowhttp://en.wikipedia.org/wiki/South_Polehttp://en.wikipedia.org/wiki/Southern_Hemispherehttp://en.wikipedia.org/wiki/North_Polehttp://en.wikipedia.org/wiki/Northern_Hemispherehttp://en.wikipedia.org/wiki/Rainbandhttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-53http://en.wikipedia.org/wiki/Nimbostratushttp://en.wikipedia.org/wiki/Precipitation_types_%28meteorology%29#Stratiformhttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-52http://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Warm_fronthttp://en.wikipedia.org/wiki/European_windstormhttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-MarinersWeatherLog-51http://en.wikipedia.org/wiki/Extratropical_cyclonehttp://en.wikipedia.org/wiki/Korean_Peninsulahttp://en.wikipedia.org/wiki/Snowhttp://en.wikipedia.org/w/index.php?title=Precipitation_%28meteorology%29&action=edit&section=16http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-49http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-49http://en.wikipedia.org/wiki/Mojave_Deserthttp://en.wikipedia.org/wiki/Great_Basinhttp://en.wikipedia.org/wiki/Sierra_Nevada_%28U.S.%29http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-48http://en.wikipedia.org/wiki/Andeshttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-47http://en.wikipedia.org/wiki/Trade_winds


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Rainfall distribution by month inCairnsshowing the extent of the wet season at that locationSee also:MonsoonandTropical cyclone

Main article:Wet season

The wet, or rainy, season is the time of year, covering one or more months, when most of the average annual

rainfallin a region falls.[58]

The term green season is also sometimes used as aeuphemismby tourist

authorities.[59]

Areas with wet seasons are dispersed across portions of thetropicsandsubtropics.[60]

Savanna

climates and areas withmonsoonregimes have wet summers and dry winters. Tropical rainforests technicallydo not have dry or wet seasons, since their rainfall is equally distributed through the year .

[61]Some areas with

pronounced rainy seasons will see a break in rainfall mid-season when the intertropical convergence zoneormonsoon troughmove poleward of their location during the middle of the warm season.[24]When the wet

season occurs during the warm season, orsummer, rain falls mainly during the late afternoon and early

evening hours. The wet season is a time whenair qualityimproves,[62]

freshwater quality improves,[63][64]

and

vegetation grows significantly.Soilnutrients diminish and erosion increases.[24]

Animals have adaptation andsurvival strategies for the wetter regime. 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 .[65]

Tropical cyclones, a source of very heavy rainfall, consist of large air masses several hundred miles acrosswith low pressure at the centre and with winds blowing inward towards the centre in either a clockwisedirection (southern hemisphere) or counterclockwise (northern hemisphere).[66]Althoughcyclonescan 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.[67]

Areas in their

path can receive a year's worth of rainfall from a tropical cyclone passage.[68]

[edit] Large-scale geographical distribution

See also:Earth rainfall climatology

On the large scale, the highest precipitation amounts outside topography fall in the tropics, closely tied to theIntertropical Convergence Zone, itself the ascending branch of theHadley cell. Mountainous locales near the

equator in Colombia are amongst the wettest places on Earth.[69]

North and south of this are regions of

descending air that formsubtropical ridgeswhere precipitation is low;[70]

the land surface underneath isusually arid, which forms most of the Earth's deserts.[71]An exception to this rule is in Hawaii, where upslopeflow due to thetrade windslead to one of the wettest locations on Earth.[72]Otherwise, the flow of the

Westerliesinto the Rocky Mountains lead to the wettest, and at elevation snowiest,[73]

locations withinNorth

America. InAsiaduring the wet season, the flow of moist air into theHimalayasleads to some of thegreatest rainfall amounts measured on Earth in northeastIndia.
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ia.org/wiki/Earth_rainfall_climatologyhttp://en.wikipedia.org/wiki/Earth_rainfall_climatologyhttp://en.wikipedia.org/wiki/Earth_rainfall_climatologyhttp://en.wikipedia.org/wiki/Intertropical_Convergence_Zonehttp://en.wikipedia.org/wiki/Intertropical_Convergence_Zonehttp://en.wikipedia.org/wiki/Hadley_cellhttp://en.wikipedia.org/wiki/Hadley_cellhttp://en.wikipedia.org/wiki/Hadley_cellhttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-NCDCxrain-68http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-NCDCxrain-68http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-NCDCxrain-68http://en.wikipedia.org/wiki/Subtropical_ridgehttp://en.wikipedia.org/wiki/Subtropical_ridgehttp://en.wikipedia.org/wiki/Subtropical_ridgehttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-69http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-69http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-69http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-70http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-70http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-70http://en.wikipedia.org/wiki/Trade_windhttp://en.wikipedia.org/wiki/Trade_windhttp://en.wikipedia.org/wiki/Trade_windhttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-71http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-71http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-71http://en.wikipedia.org/wiki/Westerlieshttp://en.wikipedia.org/wiki/Westerlieshttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-72http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-72http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-72http://en.wikipedia.org/wiki/North_Americahttp://en.wikipedia.org/wiki/North_Americahttp://en.wikipedia.org/wiki/North_Americahttp://en.wikipedia.org/wiki/North_Americahttp://en.wikipedia.org/wiki/Asiahttp://en.wikipedia.org/wiki/Asiahttp://en.wikipedia.org/wiki/Asiahttp://en.wikipedia.org/wiki/Himalayashttp://en.wikipedia.org/wiki/Himalayashttp://en.wikipedia.org/wiki/Himalayashttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/File:Cairns_climate.svghttp://en.wikipedia.org/wiki/File:Cairns_climate.svghttp://en.wikipedia.org/wiki/File:Cairns_climate.svghttp://en.wikipedia.org/wiki/File:Cairns_climate.svghttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Himalayashttp://en.wikipedia.org/wiki/Asiahttp://en.wikipedia.org/wiki/North_Americahttp://en.wikipedia.org/wiki/North_Americahttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-72http://en.wikipedia.org/wiki/Westerlieshttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-71http://en.wikipedia.org/wiki/Trade_windhttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-70http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-69http://en.wikipedia.org/wiki/Subtropical_ridgehttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-NCDCxrain-68http://en.wikipedia.org/wiki/Hadley_cellhttp://en.wikipedia.org/wiki/Intertropical_Convergence_Zonehttp://en.wikipedia.org/wiki/Earth_rainfall_climatologyhttp://en.wikipedia.org/w/index.php?title=Precipitation_%28meteorology%29&action=edit&section=18http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-67http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-2005_EPac_outlook-66http://en.wikipedia.org/wiki/Cyclonehttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-65http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-Marti_J._Van_Liere.2C_Eric-Alain_D._Ategbo.2C_Jan_Hoorweg.2C_Adel_P._Den_Hartog.2C_and_Joseph_G._A._J._Hautvast_1994_479.E2.80.93488-64http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-JS-23http://en.wikipedia.org/wiki/Soilhttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-62http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-62http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-61http://en.wikipedia.org/wiki/Air_qualityhttp://en.wikipedia.org/wiki/Summerhttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-JS-23http://en.wikipedia.org/wiki/Monsoon_troughhttp://en.wikipedia.org/wiki/Intertropical_convergence_zonehttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-Hyde-60http://en.wikipedia.org/wiki/Monsoonhttp://en.wikipedia.org/wiki/Savannahttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-59http://en.wikipedia.org/wiki/Subtropicshttp://en.wikipedia.org/wiki/Tropicshttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-58http://en.wikipedia.org/wiki/Euphemismhttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%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[edit] Measurement

Standard rain gaugeSee also:Rain gauge,Disdrometer, andSnow gauge

The standard way of measuring rainfall or snowfall is the standard rain gauge, which can be found in100 mm (4 in) plastic and 200 mm (8 in) metal varieties.[74]The inner cylinder is filled by 25 mm (1 in) of

rain, with overflow flowing into the outer cylinder. Plastic gauges have markings on the inner cylinder down

to 0.25 mm (0.01 in) resolution, while metal gauges require use of a stick designed with the appropriate0.25 mm (0.01 in) markings. After the inner cylinder is filled, the amount inside it is discarded, then filledwith 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 gauges are used in the winter by removing the funnel

and inner cylinder and allowing snow and freezing rain to collect inside the outer cylinder. Some add anti-freeze to their gauge so they do not have to melt the snow or ice that falls into the gauge.[75]Once the

snowfall/ice is finished accumulating, or as 300 mm (12 in) is approached, one can either bring it inside to

melt, or use lukewarm water to fill the inner cylinder with in order to melt the frozen precipitation in theouter cylinder, keeping track of the warm fluid added, which is subsequently subtracted from the overall total

once all the ice/snow is melted.[76]

Other types of gauges include the popular wedge gauge (the cheapest rain gauge and most fragile), thetipping bucket rain gauge, and the weighing rain gauge.[77]The wedge and tipping bucket gauges 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 gauge is kept much above freezing. Weighing gauges withantifreeze 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 gauge if left out in the open, but its accuracy will depend on what ruler is used to measure the rainwith. Any of the above rain gauges can be made at home, with enough know-how.[78]
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When a precipitation measurement is made, various networks exist across the United States and elsewhere

where rainfall measurements can be submitted through the Internet, such asCoCoRAHSor GLOBE.[79][80]

Ifa network is not available in the area where one lives, the nearest local weather office will likely be interested

in the measurement.[81]

[edit] Return period

See also:100-year flood

The likelihood or probability of an event with a specified intensity and duration, is called thereturn periodorfrequency.

[82]The intensity of a storm can be predicted for any return period and storm duration, from charts

based on historic data for the location.[83]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 percent likelihood any given year. The rainfall

will be greater and the flooding will be worse than the worst storm expected 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 ofonly once in a century, so has a 1 percent likelihood in any given year. The rainfall 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.[84]

[edit] Role in Kppen climate classification

Updated Kppen-Geiger climate map[85]

Af

Am

Aw

BWh

BWk

BShBSk

Csa

Csb

Cwa

Cwb

Cfa

Cfb

Cfc

Dsa

Dsb

DscDsd

Dwa

Dwb

DwcDwd

Dfa

Dfb

DfcDfd

ET

EF

Main article:Kppen climate classification

The Kppen classification depends on average monthly values of temperature and precipitation. The mostcommonly used form of the Kppen classification has five primary types labeled A through E. Specifically,

the primary types are A, tropical; B, dry; C, mild mid-latitude; D, cold mid-latitude; and E, polar. The five

primary classifications can be further divided into secondary classifications such asrain forest,monsoon,tropical savanna,humid subtropical,humid continental,oceanic climate,Mediterranean climate,steppe,

subarctic climate,tundra,polar ice cap, anddesert.
http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-77http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-77http://en.wikipedia.org/wiki/Community_Collaborative_Rain,_Hail_and_Snow_networkhttp://en.wikipedia.org/wiki/Community_Collaborative_Rain,_Hail_and_Snow_networkhttp://en.wikipedia.org/wiki/Community_Collaborative_Rain,_Hail_and_Snow_networkhttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-78http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-78http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-78http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-80http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-80http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-80http://en.wikipedia.org/w/index.php?title=Precipitation_%28meteorology%29&action=edit&section=20http://en.wikipedia.org/wiki/100-year_floodhttp://en.wikipedia.org/wiki/100-year_floodhttp://en.wikipedia.org/wiki/100-year_floodhttp://en.wikipedia.org/wiki/Return_periodhttp://en.wikipedia.org/wiki/Return_periodhttp://en.wikipedia.org/wiki/Return_periodhttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-81http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-81http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-81http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-82http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-82http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-82http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-83http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-83http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-83http://en.wikipedia.org/w/index.php?title=Precipitation_%28meteorology%29&action=edit&section=21http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-84http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-84http://en.wikipedia.org/wiki/Equatorial_climatehttp://en.wikipedia.org/wiki/Equatorial_climatehttp://en.wikipedia.org/wiki/Monsoonhttp://en.wikipedia.org/wiki/Monsoonhttp://en.wikipedia.org/wiki/Tropical_savanna_climatehttp://en.wikipedia.org/wiki/Tropical_savanna_climatehttp://en.wikipedia.org/wiki/Desert_climatehttp://en.wikipedia.org/wiki/Desert_climatehttp://en.wikipedia.org/wiki/Desert_climatehttp://en.wikipedia.org/wiki/Desert_climatehttp://en.wikipedia.org/wiki/Semi-arid_climatehttp://en.wikipedia.org/wiki/Semi-arid_climatehttp://en.wikipedia.org/wiki/Semi-arid_climatehttp://en.wikipedia.org/wiki/Semi-arid_climatehttp://en.wikipedia.org/wiki/Mediterranean_climatehttp://en.wikipedia.org/wiki/Mediterranean_climatehttp://en.wikipedia.org/wiki/Mediterranean_climatehttp://en.wikipedia.org/wiki/Mediterranean_climatehttp://en.wikipedia.org/wiki/Humid_subtropical_climatehttp://en.wikipedia.org/wiki/Humid_subtropical_climatehttp://en.wikipedia.org/wiki/Oceanic_climatehttp://en.wikipedia.org/wiki/Oceanic_climatehttp://en.wikipedia.org/wiki/Humid_subtropical_climatehttp://en.wikipedia.org/wiki/Humid_subtropical_climatehttp://en.wikipedia.org/wiki/Oceanic_climatehttp://en.wikipedia.org/wiki/Oceanic_climatehttp://en.wikipedia.org/wiki/Oceanic_climatehttp://en.wikipedia.org/wiki/Oceanic_climatehttp://en.wikipedia.org/wiki/Continental_climatehttp://en.wikipedia.org/wiki/Continental_climatehttp://en.wikipedia.org/wiki/Continental_climatehttp://en.wikipedia.org/wiki/Continental_climatehttp://en.wikipedia.org/wiki/Continental_climatehttp://en.wikipedia.org/wiki/Continental_climatehttp://en.wikipedia.org/wiki/Continental_climatehttp://en.wikipedia.org/wiki/Continental_climatehttp://en.wikipedia.org/wiki/Humid_continental_climatehttp://en.wikipedia.org/wiki/Humid_continental_climatehttp://en.wikipedia.org/wiki/Humid_continental_climatehttp://en.wikipedia.org/wiki/Humid_continental_climatehttp://en.wikipedia.org/wiki/Subarctic_climatehttp://en.wikipedia.org/wiki/Subarctic_climatehttp://en.wikipedia.org/wiki/Subarctic_climatehttp://en.wikipedia.org/wiki/Subarctic_climatehttp://en.wikipedia.org/wiki/Humid_continental_climatehttp://en.wikipedia.org/wiki/Humid_continental_climatehttp://en.wikipedia.org/wiki/Humid_continental_climatehttp://en.wikipedia.org/wiki/Humid_continental_climatehttp://en.wikipedia.org/wiki/Subarctic_climatehttp://en.wikipedia.org/wiki/Subarctic_climatehttp://en.wikipedia.org/wiki/Subarctic_climatehttp://en.wikipedia.org/wiki/Subarctic_climatehttp://en.wikipedia.org/wiki/Tundra_climatehttp://en.wikipedia.org/wiki/Tundra_climatehttp://en.wikipedia.org/wiki/Ice_cap_climatehttp://en.wikipedia.org/wiki/Ice_cap_climatehttp://en.wikipedia.org/wiki/K%C3%B6ppen_climate_classificationhttp://en.wikipedia.org/wiki/K%C3%B6ppen_climate_classificationhttp://en.wikipedia.org/wiki/K%C3%B6ppen_climate_classificationhttp://en.wikipedia.org/wiki/Rain_foresthttp://en.wikipedia.org/wiki/Rain_foresthttp://en.wikipedia.org/wiki/Rain_foresthttp://en.wikipedia.org/wiki/Monsoonhttp://en.wikipedia.org/wiki/Monsoonhttp://en.wikipedia.org/wiki/Monsoonhttp://en.wikipedia.org/wiki/Tropical_savannahttp://en.wikipedia.org/wiki/Tropical_savannahttp://en.wikipedia.org/wiki/Humid_subtropicalhttp://en.wikipedia.org/wiki/Humid_subtropicalhttp://en.wikipedia.org/wiki/Humid_subtropicalhttp://en.wikipedia.org/wiki/Humid_continentalhttp://en.wikipedia.org/wiki/Humid_continentalhttp://en.wikipedia.org/wiki/Humid_continentalhttp://en.wikipedia.org/wiki/Oceanic_climatehttp://en.wikipedia.org/wiki/Oceanic_climatehttp://en.wikipedia.org/wiki/Oceanic_climatehttp://en.wikipedia.org/wiki/Mediterranean_climatehttp://en.wikipedia.org/wiki/Mediterranean_climatehttp://en.wikipedia.org/wiki/Mediterranean_climatehttp://en.wikipedia.org/wiki/Steppehttp://en.wikipedia.org/wiki/Steppehttp://en.wikipedia.org/wiki/Steppehttp://en.wikipedia.org/wiki/Subarctic_climatehttp://en.wikipedia.org/wiki/Subarctic_climatehttp://en.wikipedia.org/wiki/Tundrahttp://en.wikipedia.org/wiki/Tundrahttp://en.wikipedia.org/wiki/Tundrahttp://en.wikipedia.org/wiki/Polar_ice_caphttp://en.wikipedia.org/wiki/Polar_ice_caphttp://en.wikipedia.org/wiki/Polar_ice_caphttp://en.wikipedia.org/wiki/Deserthttp://en.wikipedia.org/wiki/Deserthttp://en.wikipedia.org/wiki/Deserthttp://en.wikipedia.org/wiki/File:World_Koppen_Map.pnghttp://en.wikipedia.org/wiki/File:World_Koppen_Map.pnghttp://en.wikipedia.org/wiki/File:World_Koppen_Map.pnghttp://en.wikipedia.org/wiki/File:World_Koppen_Map.pnghttp://en.wikipedia.org/wiki/Deserthttp://en.wikipedia.org/wiki/Polar_ice_caphttp://en.wikipedia.org/wiki/Tundrahttp://en.wikipedia.org/wiki/Subarctic_climatehttp://en.wikipedia.org/wiki/Steppehttp://en.wikipedia.org/wiki/Mediterranean_climatehttp://en.wikipedia.org/wiki/Oceanic_climatehttp://en.wikipedia.org/wiki/Humid_continentalhttp://en.wikipedia.org/wiki/Humid_subtropicalhttp://en.wikipedia.org/wiki/Tropical_savannahttp://en.wikipedia.org/wiki/Monsoonhttp://en.wikipedia.org/wiki/Rain_foresthttp://en.wikipedia.org/wiki/K%C3%B6ppen_climate_classificationhttp://en.wikipedia.org/wiki/Ice_cap_climatehttp://en.wikipedia.org/wiki/Tundra_climatehttp://en.wikipedia.org/wiki/Subarctic_climatehttp://en.wikipedia.org/wiki/Subarctic_climatehttp://en.wikipedia.org/wiki/Humid_continental_climatehttp://en.wikipedia.org/wiki/Humid_continental_climatehttp://en.wikipedia.org/wiki/Subarctic_climatehttp://en.wikipedia.org/wiki/Subarctic_climatehttp://en.wikipedia.org/wiki/Humid_continental_climatehttp://en.wikipedia.org/wiki/Humid_continental_climatehttp://en.wikipedia.org/wiki/Continental_climatehttp://en.wikipedia.org/wiki/Continental_climatehttp://en.wikipedia.org/wiki/Continental_climatehttp://en.wikipedia.org/wiki/Continental_climatehttp://en.wikipedia.org/wiki/Oceanic_climatehttp://en.wikipedia.org/wiki/Oceanic_climatehttp://en.wikipedia.org/wiki/Humid_subtropical_climatehttp://en.wikipedia.org/wiki/Oceanic_climatehttp://en.wikipedia.org/wiki/Humid_subtropical_climatehttp://en.wikipedia.org/wiki/Mediterranean_climatehttp://en.wikipedia.org/wiki/Mediterranean_climatehttp://en.wikipedia.org/wiki/Semi-arid_climatehttp://en.wikipedia.org/wiki/Semi-arid_climatehttp://en.wikipedia.org/wiki/Desert_climatehttp://en.wikipedia.org/wiki/Desert_climatehttp://en.wikipedia.org/wiki/Tropical_savanna_climatehttp://en.wikipedia.org/wiki/Monsoonhttp://en.wikipedia.org/wiki/Equatorial_climatehttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-84http://en.wikipedia.org/w/index.php?title=Precipitation_%28meteorology%29&action=edit&section=21http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-83http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-82http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-81http://en.wikipedia.org/wiki/Return_periodhttp://en.wikipedia.org/wiki/100-year_floodhttp://en.wikipedia.org/w/index.php?title=Precipitation_%28meteorology%29&action=edit&section=20http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-80http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-78http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29#cite_note-78http://en.wikipedia.org/wiki/Community_Collaborative_Rain,_Hail_and_Snow_network


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Rain forests are characterized by highrainfall, with definitions setting minimum normal annual rainfall

between 1,750 millimetres (69 in) and 2,000 millimetres (79 in).[86]

A tropical savanna is agrasslandbiomelocated insemi-aridto semi-humidclimate regions ofsubtropicalandtropicallatitudes, with rainfall between

750 millimetres (30 in) and 1,270 millimetres (50 in) a year. They are widespread on Africa, and are also

found in India, the northern parts of South America,Malaysia, and Australia.[87]

The humid subtropicalclimate zone where winter rainfall (and sometimessnowfall) is associated with largestormsthat the

westerliessteer from west to east. Most summer rainfall occurs duringthunderstormsand from occasional

tropical cyclones.

[88]

Humid subtropical climates lie on the east side continents, roughly betweenlatitudes20 and 40 degrees away from the equator.[89]

An oceanic (or maritime) climate is typically found along the west coasts at the middle latitudes of all theworld's continents, bordering cool oceans, as well as southeastern Australia, and is accompanied by plentiful

precipitation year round.[90]The Mediterranean climate regime resembles the climate of the lands in the

Mediterranean Basin, parts of western North America, parts ofWesternandSouth Australia, in southwesternSouth Africaand in parts of centralChile. The climate is characterized by hot, dry summers and cool, wet

winters.[91]A steppe is a drygrassland.[92]Subarctic climates are cold with continuouspermafrostand little

precipitation.[93]

[edit] Effect on agriculture

Rainfall estimates for southern Japan and the surrounding region from July 20 to 27, 2009.

Precipitation, especially rain, has a dramatic effect onagriculture. Allplantsneed at least some water tosurvive, therefore rain (being the most effective means of watering) is important toagriculture. While aregular rain pattern is usually vital to healthyplants, too much or too little rainfall can be harmful, even

devastating tocrops.Droughtcan kill crops and increase erosion,[94]

while overly wet weather can cause

harmfulfungusgrowth.[95]

Plantsneed varying amounts of rainfall to survive. For example, certaincactirequire small amounts of water,[96]while tropical plants may need up to hundreds of inches of rain per year to

survive.

In areas with wet and dry seasons,soilnutrients diminish and erosion increases during the wet season.[24]Animals have adaptation and survival strategies for the wetter regime. The previous dry season leads to food

shortages into the wet season, as the crops have yet to mature.[97]

Developing countries have noted that their

populations show seasonal weight fluctuations due to food shortages seen before the first harvest, whichoccurs late in the wet season.[65]

[edit] Changes due to global warming

See also:Global warming
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Increasing temperatures tend to increase evaporation which leads to more precipitation. Precipitation has

generally increased over land north of 30N from 1900 through 2005 but has declined over the tropics sincethe 1970s. Globally there has been no statistically significant overall trend in precipitation over the past

century, although trends have varied widely by region and over time. Eastern portions of North and South

America, northern Europe, and northern and central Asia have become wetter. The Sahel, the Mediterranean,southern Africa and parts of southern Asia have become drier. There has been an increase in the number of

heavy precipitation events over many areas during the past century, as well as an increase since the 1970s in

the prevalence of droughts

especially in the tropics and subtropics. Changes in precipitation andevaporation over the oceans are suggested by the decreased salinity of mid- and high-latitude waters(implying more precipitation), along with increased salinity in lower latitudes (implying less precipitation,

more evaporation, or both). Over the contiguous United States, total annual precipitation increased at an

average rate of 6.1 percent per century since 1900, with the greatest increases within the East North Centralclimate region (11.6 percent per century) and the South (11.1 percent). Hawaii was the only region to show a

decrease (-9.25 percent).[98]

[edit] Changes due to urban heat island

Image ofAtlanta, Georgia, showing temperature distribution, with hot areas appearing white

See also:Urban heat island

The urban heat island warms cities 0.6 C (1.1 F) to 5.6 C (10.1 F) above surrounding suburbs and rural

areas. This extra heat leads to greater upward motion, which can induce additional shower and thunderstorm

activity. Rainfall rates downwind of cities are increased between 48% and 116%. Partly as a result of thiswarming, monthly rainfall is about 28% greater between 20 miles (32 km) to 40 miles (64 km) downwind of

cities, compared with upwind.[99]

Some cities induce a total precipitation increase of 51%.[100]

[edit] Forecasting

Main article:Quantitative precipitation forecast

Example of a five day rainfall forecast from theHydrometeorological Prediction Center
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The Quantitative Precipitation Forecast (abbreviated QPF) is the expected amount of liquid precipitation

accumulated over a specified time period over a specified area.[101]

A QPF will be specified when ameasurable 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 fromobservations with fine detail.[102]Starting in the mid to late 1990s, QPFs were used within hydrologic

forecast models to simulate impact to rivers throughout the United States.[103]Forecast modelsshow

significant sensitivity to humidity levels within theplanetary boundary layer, or in the lowest levels of theatmosphere, which decreases with height.[104]

QPF can be generated on a quantitative, forecasting amounts,or a qualitative, forecasting theprobability of a specific amount, basis.[105]Radar imagery forecasting

techniques show higherskillthan model forecasts within six to seven hours of the time of the radar image.

The forecasts can be verified through use ofrain gaugemeasurements,weather radarestimates, or acombination of both. Various skill scores can be determined to measure the value of the rainfall forecast .[106]

Rain is liquidprecipitation, as opposed to non-liquid kinds of precipitation such assnow,hailandsleet. Rain

requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of

water near and above the Earth's surface. On Earth, it is the condensationof atmosphericwater vaporinto

dropsofwaterheavy enough to fall, often making it to the surface. Two processes, possibly acting together,

can lead to air becoming saturated leading to rainfall: cooling the air or adding water vapor to the air. Virgais 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. Rain drops range in size from oblate, pancake-like shapes for larger drops, to small spheres for smallerdrops.

Moisture moving along three-dimensional zones of temperature and moisture contrasts known asweatherfrontsis the major method of rain production. If enough moisture and upward motion is present, precipitation

falls from convective clouds (those with strong upward vertical motion) such ascumulonimbus

(thunderstorms) which can organize into narrowrainbands. In mountainous areas, heavy precipitation ispossible whereupslope flowis maximized withinwindwardsides of theterrainat elevation which forces

moist air to condense and fall out as rainfall along the sides of mountains. On the leeward side of mountains,desert climates can exist due to the dry air caused by downslope flow which causes heating and drying of the

air mass. The movement of themonsoon trough, orintertropical convergence zone, bringsrainy seasonstosavannahclimes. Rain is the primary source of freshwater for most areas of the world, providing suitable

conditions for diverseecosystems, as well as water forhydroelectric power plantsand cropirrigation.

Rainfall is measured through the use ofrain gauges. Rainfall amounts are estimated actively byweather radarand passively byweather satellites.

Theurban heat islandeffect leads to increased rainfall, both in amounts and intensity, downwind of cities.Global warmingis also causing changes in the precipitation pattern globally, including wetter conditions

across easternNorth Americaand drier conditions in the tropics. Precipitation is a major component of the

water cycle, and is responsible for depositing most of thefresh wateron theplanet. The globally averaged

annual precipitation is 990 millimetres (39 in).Climateclassification systems such as theKppen climateclassificationsystem use average annual rainfall to help differentiate between differing climate regimes.

Antarctica is the Earth's driest continent. Rain is also known or suspected on other worlds, composed of

methane,iron,neon, andsulfuric acidrather than water.
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it rains because the water droplets in the clouds increase too much and the water becomes too heavy...

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