Cumulonimbus (from

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power ...

''cumulus'', "heaped" and ''nimbus'', "rainstorm") is a dense, towering vertical

cloud In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may ...

, typically forming from

water vapor (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 J/( kg·K) , - , Heat of vaporization , 2.27 MJ/kg , - , Heat capacity , 1.864 kJ/(kg·K) Water vapor, water vapour or aqueous vapor is the gaseous p ...

condensing in the lower

troposphere The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From ...

that builds upward carried by powerful buoyant air currents. Above the lower portions of the cumulonimbus the water vapor becomes

ice crystal Ice crystals are solid ice exhibiting atomic ordering on various length scales and include hexagonal columns, hexagonal plates, dendritic crystals, and diamond dust. Formation The hugely symmetric shapes are due to depositional growth, na ...

s, such as

snow Snow comprises individual ice crystals that grow while suspended in the atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet ...

and

graupel Graupel (; ), also called soft hail, hominy snow, or snow pellets, is precipitation that forms when supercooled water droplets in air are collected and freeze on falling snowflakes, forming balls of crisp, opaque rime. Graupel is distinct fro ...

, the interaction of which can lead to

hail Hail is a form of solid precipitation. It is distinct from ice pellets (American English "sleet"), though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets generally fal ...

and to

lightning Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an average ...

formation, respectively. When occurring as a

thunderstorm A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are somet ...

these clouds may be referred to as thunderheads. Cumulonimbus can form alone, in clusters, or along

squall line A squall line, or more accurately a quasi-linear convective system (QLCS), is a line of thunderstorms, often forming along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front (which often are accompa ...

s. These clouds are capable of producing lightning and other dangerous

severe weather Severe weather is any dangerous meteorological phenomenon with the potential to cause damage, serious social disruption, or loss of human life. Types of severe weather phenomena vary, depending on the latitude, altitude, topography, and atmos ...

, such as

tornado A tornado is a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, alt ...

es, hazardous

wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ...

s, and large hailstones. Cumulonimbus progress from overdeveloped

cumulus congestus cloud Cumulus congestus clouds, also known as towering cumulus, are a form of cumulus that can be based in the low or middle height ranges. They achieve considerable vertical development in areas of deep, moist convection. They are an intermediate stage ...

s and may further develop as part of a

supercell A supercell is a thunderstorm characterized by the presence of a mesocyclone: a deep, persistently rotating updraft. Due to this, these storms are sometimes referred to as rotating thunderstorms. Of the four classifications of thunderstorms ...

. Cumulonimbus is abbreviated Cb.

Appearance

Towering cumulonimbus clouds are typically accompanied by smaller

cumulus Cumulus clouds are clouds which have flat bases and are often described as "puffy", "cotton-like" or "fluffy" in appearance. Their name derives from the Latin ''cumulo-'', meaning ''heap'' or ''pile''. Cumulus clouds are low-level clouds, gener ...

clouds. The cumulonimbus base may extend several kilometres (miles) across, or be as small as several tens of metres (yards) across, and occupy low to upper altitudes within the troposphere - formed at altitude from approximately . Peaks typically reach to as much as , with extreme instances as high as or more. Well-developed cumulonimbus clouds are characterized by a flat,

anvil An anvil is a metalworking tool consisting of a large block of metal (usually forged or cast steel), with a flattened top surface, upon which another object is struck (or "worked"). Anvils are as massive as practical, because the highe ...

-like top (anvil dome), caused by

wind shear Wind shear (or windshear), sometimes referred to as wind gradient, is a difference in wind speed and/or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical or horizon ...

inversion Inversion or inversions may refer to: Arts * , a French gay magazine (1924/1925) * ''Inversion'' (artwork), a 2005 temporary sculpture in Houston, Texas * Inversion (music), a term with various meanings in music theory and musical set theory * ...

at the

equilibrium level In meteorology, the equilibrium level (EL), or level of neutral buoyancy (LNB), or limit of convection (LOC), is the height at which a rising parcel of air is at the same temperature as its environment. This means that unstable air is now stable ...

near the

tropopause The tropopause is the atmospheric boundary that demarcates the troposphere from the stratosphere; which are two of the five layers of the atmosphere of Earth. The tropopause is a thermodynamic gradient-stratification layer, that marks the end of ...

. The shelf of the anvil may precede the main cloud's vertical component for many kilometres (miles), and be accompanied by lightning. Occasionally, rising air parcels surpass the equilibrium level (due to momentum) and form an

overshooting top An overshooting top (or penetrating top) is a dome-like protrusion shooting out of the top of the anvil of a thunderstorm and into the lower stratosphere. When an overshooting top is present for 10 minutes or longer, it is a strong indication th ...

culminating at the maximum parcel level. When vertically developed, this largest of all clouds usually extends through all three cloud regions. Even the smallest cumulonimbus cloud dwarfs its neighbors in comparison.

Species

* Cumulonimbus calvus: cloud with puffy top, similar to cumulus congestus which it develops from; under the correct conditions it can become a cumulonimbus capillatus. * Cumulonimbus capillatus: cloud with cirrus-like, fibrous-edged top. File:Wagga-Cumulonimbus.jpg, Cumulonimbus calvus Storm cloud.jpg, A clearly developed cumulonimbus fibrous-edged top capillatus File:Cloudwithlightning.jpg, A freeze-frame of a Cumulonimbus cloud in the distance exposing a flash of lightning

Types

* Cumulonimbus flammagenitus (pyrocumulonimbus): rapidly growing cloud forming from non-atmospheric heat and condensation nuclei sources such

wildfire A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identi ...

s and

volcanic eruption Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are ...

Willow Fire AZ 7 8 2004 SE burnout 035-001

Supplementary features

Accessory clouds

* Arcus (including roll and shelf clouds): low, horizontal cloud formation associated with the leading edge of thunderstorm

outflow Outflow may refer to: * Capital outflow, the capital leaving a particular economy * Bipolar outflow, in astronomy, two continuous flows of gas from the poles of a star * Outflow (hydrology), the discharge of a lake or other reservoir system *Outflo ...

. * Pannus: accompanied by a lower layer of fractus species cloud forming in precipitation. * Pileus (species calvus only): small cap-like cloud over parent cumulonimbus. *

Velum Velum may refer to: Human anatomy * Superior medullary velum, anterior medullary velum or valve of Vieussens, white matter, in the brain, which stretches between the superior cerebellar peduncles ** Frenulum of superior medullary velum, a slightl ...

: a thin horizontal sheet that forms around the middle of a cumulonimbus.

Supplementary features

Incus The ''incus'' (plural incudes) or anvil is a bone in the middle ear. The anvil-shaped small bone is one of three ossicles in the middle ear. The ''incus'' receives vibrations from the ''malleus'', to which it is connected laterally, and transmi ...

(species capillatus only): cumulonimbus with flat anvil-like cirriform top caused by wind shear where the rising air currents hit the

layer at the tropopause. * Mamma or mammatus: consisting of bubble-like protrusions on the underside. * Tuba: column hanging from the cloud base which can develop into a

funnel cloud A funnel cloud is a funnel-shaped cloud of condensed water droplets, associated with a rotating column of wind and extending from the base of a cloud (usually a cumulonimbus or towering cumulus cloud) but not reaching the ground or a water s ...

or tornado. They are known to drop very low, sometimes just above ground level. * Flanking line is a line of small cumulonimbus or cumulus generally associated with severe thunderstorms. * An

is a dome that rises above the thunderstorm; it is associated with severe weather.

Precipitation-based supplementary features

Rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water ...

: precipitation that reaches the ground as liquid, often in a precipitation shaft. *

Virga In meteorology, a virga, also called a dry storm, is an observable streak or shaft of precipitation falling from a cloud that evaporates or sublimates before reaching the ground. A shaft of precipitation that does not evaporate before reac ...

: precipitation that evaporates before reaching the ground. File:Rolling-thunder-cloud.jpg, Arcus cloud (shelf cloud) leading a thunderstorm File:Cumulus pileus.jpg, A cap (pileus) atop a congestus File:Fly00890 - Flickr - NOAA Photo Library.jpg, Incus with a velum edge File:Mammatus clouds regina sk june 2012.JPG, Mammatocumulus with drooping pouches File:Cumulonimbus tuba.jpg, A funnel cloud (tuba) over the Netherlands File:Anvil shaped cumulus panorama edit.jpg, Flanking line in front of a strong thunderstorm File:Cumulonimbus13 - NOAA.jpg, An overshooting top is a dome of clouds atop a cumulonimbus File:Sunnystormcloud.jpg, Cumulonimbus calvus against sunlight with rain falling beneath it as a rain shaft. File:Cb virga 1.JPG, Rain evaporating before reaching the ground (virga)

Effects

Cumulonimbus storm cells can produce torrential

rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water ...

of a

convective Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...

nature (often in the form of a rain shaft) and

flash flood A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, or tropical storm, or by meltwater from ice or snow flowing ...

ing, as well as

straight-line winds In meteorology, a downburst is a strong downward and outward gushing wind system that emanates from a point source above and blows radially, that is, in straight lines in all directions from the area of impact at surface level. Capable of pro ...

. Most storm cells die after about 20 minutes, when the

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hai ...

causes more

downdraft In meteorology, an updraft is a small-scale current of rising air, often within a cloud. Overview Localized regions of warm or cool air will exhibit vertical movement. A mass of warm air will typically be less dense than the surrounding regi ...

than

updraft In meteorology, an updraft is a small-scale current of rising air, often within a cloud. Overview Localized regions of warm or cool air will exhibit vertical movement. A mass of warm air will typically be less dense than the surrounding region ...

, causing the energy to dissipate. If there is sufficient instability and moisture in the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. ...

, however (on a hot summer day, for example), the outflowing moisture and gusts from one storm cell can lead to new cells forming just a few kilometres (miles) from the former one a few tens of minutes later or in some cases hundreds of kilometres (miles) away many hours later. This process cause thunderstorm formation (and decay) to last for several hours or even over multiple days. Cumulonimbus clouds can also occur as a dangerous winter storms called "

thundersnow Thundersnow, also known as a winter thunderstorm or a thundersnowstorm, is a kind of thunderstorm with snow falling as the primary precipitation instead of rain. It is considered a rare and unusual phenomenon. It typically falls in regions of s ...

" which are associated with particularly intense snowfall rates and with

blizzard A blizzard is a severe snowstorm characterized by strong sustained winds and low visibility, lasting for a prolonged period of time—typically at least three or four hours. A ground blizzard is a weather condition where snow is not falling ...

conditions when accompanied by strong winds that further reduce

visibility The visibility is the measure of the distance at which an object or light can be clearly discerned. In meteorology it depends on the transparency of the surrounding air and as such, it is unchanging no matter the ambient light level or time of ...

. However, cumulonimbus clouds are most common in

tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

regions and are also frequent in moist environments during the warm season in the

middle latitudes The middle latitudes (also called the mid-latitudes, sometimes midlatitudes, or moderate latitudes) are a spatial region on Earth located between the Tropic of Cancer (latitudes 23°26'22") to the Arctic Circle (66°33'39"), and Tropic of Capri ...

. A

dust storm A dust storm, also called a sandstorm, is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Fine particles are tra ...

caused by a cumulonimbus downburst is a

haboob A haboob ( ar, هَبوب, lit=blasting/drifting, translit=habūb) is a type of intense dust storm carried on an atmospheric gravity current, also known as a weather front. Haboobs occur regularly in dry land area regions throughout the world. ...

Hazards to aviation

Cumulonimbus are a notable hazard to aviation due most importantly to potent wind currents but also reduced visibility and lightning, as well as icing and hail if flying inside the cloud. Within and in the vicinity of thunderstorms there is significant

turbulence In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...

and

clear-air turbulence In meteorology, clear-air turbulence (CAT) is the turbulent movement of air masses in the absence of any visual clues, such as clouds, and is caused when bodies of air moving at widely different speeds meet. The atmospheric region most suscep ...

(particularly

downwind Windward () and leeward () are terms used to describe the direction of the wind. Windward is ''upwind'' from the point of reference, i.e. towards the direction from which the wind is coming; leeward is ''downwind'' from the point of reference ...

), respectively. Wind shear within and under a cumulonimbus is often intense with

downburst In meteorology, a downburst is a strong downward and outward gushing wind system that emanates from a point source above and blows radially, that is, in straight lines in all directions from the area of impact at surface level. Capable of pro ...

s being responsible for many accidents in earlier decades before training and technological

detection {{Unreferenced, date=March 2018 In general, detection is the action of accessing information without specific cooperation from with the sender. In the history of radio communications, the term "detector" was first used for a device that detected t ...

and nowcasting measures were implemented. A small form of downburst, the microburst, is the most often implicated in crashes because of their rapid onset and swift changes in wind and aerodynamic conditions over short distances. Most downbursts are associated with visible precipitation shafts, however, dry microbursts are generally invisible to the naked eye. At least one fatal commercial airline

accident An accident is an unintended, normally unwanted event that was not directly caused by humans. The term ''accident'' implies that nobody should be blamed, but the event may have been caused by unrecognized or unaddressed risks. Most researche ...

was associated with flying through a tornado.

Life cycle or stages

In general, cumulonimbus require moisture, an unstable

air mass In meteorology, an air mass is a volume of air defined by its temperature and humidity. Air masses cover many hundreds or thousands of square miles, and adapt to the characteristics of the surface below them. They are classified according to ...

, and a lifting force in order to form. Cumulonimbus typically go through three stages: the developing stage, the mature stage (where the main cloud may reach supercell status in favorable conditions), and the dissipation stage. The average thunderstorm has a diameter and a height of approximately . Depending on the conditions present in the atmosphere, these three stages take an average of 30 minutes to go through.

Cloud types

Clouds form when the

dew point The dew point is the temperature to which air must be cooled to become saturated with water vapor, assuming constant air pressure and water content. When cooled below the dew point, moisture capacity is reduced and airborne water vapor will c ...

temperature of water is reached in the presence of condensation nuclei in the troposphere. The atmosphere is a dynamic system, and the local conditions of turbulence, uplift, and other parameters give rise to many types of clouds. Various types of cloud occur frequently enough to have been categorized. Furthermore, some atmospheric processes can make the clouds organize in distinct patterns such as

wave cloud A wave cloud is a cloud form created by atmospheric internal waves. Formation The atmospheric internal waves that form wave clouds are created as stable air flows over a raised land feature such as a mountain range, and can form either dir ...

s or actinoform clouds. These are large-scale structures and are not always readily identifiable from a single point of view.

References

External links

Clouds-Online.com Cloud Atlas with many photos and description of the different cloud genera

MetOffice.gov.uk Learn about thunderstorms and how cumulonimbus clouds form
{{DEFAULTSORT:Cumulonimbus Cloud Cirrus Cumulus Severe weather and convection

Appearance

Species

Types

Supplementary features

Accessory clouds

Supplementary features

Precipitation-based supplementary features

Effects

Hazards to aviation

Life cycle or stages

Cloud types

See also

References

External links