Cumulonimbus () 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 Water vapor, water vapour, or aqueous vapor is the gaseous phase of Properties of water, water. It is one Phase (matter), state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from th ...

condensing in the lower

troposphere The troposphere is the lowest layer of the atmosphere of Earth. It contains 80% of the total mass of the Atmosphere, planetary atmosphere and 99% of the total mass of water vapor and aerosols, and is where most weather phenomena occur. From the ...

that builds upward carried by powerful buoyant air currents. Above the lower portions of the cumulonimbus the water vapor becomes ice crystals, such as

snow Snow consists of individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water througho ...

and

graupel Graupel (; ), also called soft hail or hominy snow or granular 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. Gra ...

, the interaction of which can lead to

hail Hail is a form of solid Precipitation (meteorology), 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 hailsto ...

and to

lightning Lightning is a natural phenomenon consisting of electrostatic discharges occurring through the atmosphere between two electrically charged regions. One or both regions are within the atmosphere, with the second region sometimes occurring on ...

formation, respectively. When causing

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

s, these clouds may be called thunderheads. Cumulonimbus can form alone, in clusters, or along squall lines. 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. These vary depending on the latitude, altitude, topography, and atmospheric conditions. High ...

, such as

tornado A tornado is a violently rotating column of air that is in contact with the surface of 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, although the ...

es, hazardous

wind Wind is the natural movement of atmosphere of Earth, air or other gases relative to a planetary surface, planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heatin ...

s, and large hailstones. Cumulonimbus progress from overdeveloped

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

s and may further develop as part of a supercell. Cumulonimbus is abbreviated as Cb.

Description

Towering cumulonimbus clouds are typically accompanied by smaller

cumulus cloud Cumulus clouds are clouds that have flat cloud base, bases and are often described as puffy, cotton-like, or fluffy in appearance. Their name derives from the Latin , meaning "heap" or "pile". Cumulus clouds are low-level clouds, generally less ...

s. 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 . Normal peaks usually reach to as much as , with unusually high ones typically topping out around and extreme instances claimed to be 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 Forging, forged or Steel casting, cast steel), with a flattened top surface, upon which another object is struck (or "worked"). Anvils are massive because the hi ...

shaped top (anvil dome), caused by wind shear or inversion at the equilibrium level near the tropopause. 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 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.

Subtypes

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

Types

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

wildfire A wildfire, forest fire, or a bushfire is an unplanned and uncontrolled fire in an area of Combustibility and flammability, combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identified as a ...

s and

volcanic eruption A volcanic eruption occurs when material is expelled from a volcanic vent or fissure. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior h ...

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

=Supplementary features

= *

Incus The ''incus'' (: incudes) or anvil in the ear is one of three small bones (ossicles) in the middle ear. The incus receives vibrations from the malleus, to which it is connected laterally, and transmits these to the stapes medially. The incus i ...

(species capillatus only): cumulonimbus with flat anvil-like cirriform top caused by wind shear where the rising air currents hit the inversion 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 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 overshooting top is a dome that rises above the thunderstorm; it is associated with severe weather.

=Precipitation-based supplementary features

= *

Rain Rain is a form of precipitation where water drop (liquid), droplets that have condensation, condensed from Water vapor#In Earth's atmosphere, atmospheric water vapor fall under gravity. Rain is a major component of the water cycle and is res ...

: precipitation that reaches the ground as liquid, often in a precipitation shaft. * Virga: precipitation that evaporates before reaching the ground. File:Rolling-thunder-cloud.jpg, Arcus cloud (shelf cloud) leading a thunderstorm 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:Cb virga 1.JPG, Rain evaporating before reaching the ground (virga)

Effects

Cumulonimbus storm cells can produce torrential

rain Rain is a form of precipitation where water drop (liquid), droplets that have condensation, condensed from Water vapor#In Earth's atmosphere, atmospheric water vapor fall under gravity. Rain is a major component of the water cycle and is res ...

of a convective nature (often in the form of a rain shaft) and flash flooding, as well as straight-line winds. 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 from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...

causes more downdraft than

updraft In meteorology, an updraft (British English: ''up-draught'') is a small-scale air current, current of rising air, often within a cloud. Overview Vertical drafts, known as updrafts or downdrafts, are localized regions of warm or cool air that mov ...

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

atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

, 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 dangerous winter storms called "

thundersnow Thundersnow, also known as a winter thunderstorm or a thundersnow storm, is a thunderstorm in which snow falls as the primary precipitation instead of rain. It is considered a rare phenomenon. It typically falls in regions of strong upward moti ...

" which are associated with particularly intense snowfall rates and with

blizzard A blizzard is a severe Winter storm, 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 th ...

conditions when accompanied by strong winds that further reduce visibility. However, cumulonimbus clouds are most common in

tropical The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

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 spelled midlatitudes) or moderate latitudes, are spatial regions on either Hemispheres of Earth, hemisphere of Earth, located between the Tropic of Cancer (latitude ) and the Arctic ...

. 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 transpo ...

caused by a cumulonimbus downburst is a

haboob A haboob () is a type of intense dust storm carried by the wind of a weather front or thunderstorm. Haboobs occur regularly in arid, dry land area regions throughout the world, including off-Earth, and can be dangerous. Formation and charac ...

Aviation

Cumulonimbus are a notable hazard to aviation mostly due to potent wind currents but also reduced visibility and lightning, as well as atmospheric 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 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 turbulence, 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 mos ...

(particularly downwind), respectively. Wind shear within and under a cumulonimbus is often intense with downbursts being responsible for many accidents in earlier decades before training and technological detection 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 deliberately caused by humans. The term ''accident'' implies that the event may have been caused by Risk assessment, unrecognized or unaddressed risks. Many researchers, insurers ...

was associated with flying through a tornado.

Life cycle or stages

In general, cumulonimbus require moisture, an

unstable In dynamical systems instability means that some of the outputs or internal state (controls), states increase with time, without bounds. Not all systems that are not Stability theory, stable are unstable; systems can also be marginal stability ...

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.

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