List of cloud types

Clouds are formed in Earth's atmosphere when water evaporates into vapor from oceans, lakes, ponds, and even streams and rivers; and by evaporation or transpiration over moist areas of Earth's land surface. The vapor rises up into colder areas of the atmosphere due to convective, orographic, or frontal lifting. The water vapor attaches itself to condensation nuclei which could be anything from dust to microscopic particles of salt and debris. Once the vapor has been cooled to saturation, the cloud becomes visible. All weather-producing clouds form in the troposphere, the lowest major layer of the atmosphere. However very small amounts of water vapor can be found higher up in the stratosphere and mesosphere and may condense into very thin clouds if the air temperatures are sufficiently cold. One branch of meteorology is focused on the study of nephology or cloud physics.

Tropospheric clouds are divided into physical categories with names based upon Latin root words that indicate physical structure and process of formation. Clouds of the cirriform category are generally thin and occur mostly in the form of filaments. Two other basic categories are stratiform with clouds that are mostly sheet-like in structure, and cumuliform that appear heaped, rolled, or rippled. Two additional categories derived from the cumuliform group are stratocumuliform which are cumuliform with stratiform characteristics (rolled or rippled), and cumulonimbiform, towering cumuliform clouds often with complex structures that include cirriform tops and multiple accessory clouds.

In the troposphere, ten genus types are derived by cross-classifying the physical categories into families defined by altitude range; high, middle, low, and vertical (with low to middle cloud base). The last of these can be subdivided into two sub-families or groups to distinguish between moderate and towering vertical types. Most cloud genera are divided into species, varieties, or both, based on specific physical characteristics of the clouds.

Cirriform category clouds are only found in the high-altitude family and therefore constitute a single genus cirrus. High stratiform and stratocumuliform types carry the prefix cirro- which yield the genus names cirrostratus and cirrocumulus. Clouds of the middle-altitude family have the prefix alto- (altostratus and altocumulus) to distinguish them from the high clouds. Strato- is dropped from high and middle stratocumuliform genus names to avoid double-prefixing. Low altitude stratiform, stratocumuliform, and cumuliform genera (stratus, stratocumulus, and small cumulus) carry no height-related prefixes.

The family of vertical clouds includes thick stratiform, cumuliform, and cumulonimbiform genera, all of which can produce precipitation of significant intensity. Within this family, the group of moderate vertical clouds comprise nimbostratus and cumulus mediocris that form in the low or middle altitude range. These genus types also have no height-related prefixes, but its stratiform genus carries the prefix nimbo- to denote its ability to produce widespread precipitation. The towering vertical group has no stratiform types, but rather comprises the genus cumulonimbus, and the species cumulus congestus, a towering variant of the genus cumulus whose other species belong to the group of moderate vertical clouds.

The essentials of the modern nomenclature system for tropospheric clouds were proposed by Luke Howard, a British manufacturing chemist and an amateur meteorologist with broad interests in science, in an 1802 presentation to the Askesian Society. Since 1890, clouds have been classified and illustrated in cloud atlases.

Clouds that form above the troposphere have a generally cirriform structure, but are not given Latin names based on that characteristic. Polar stratospheric clouds form at very high altitudes in polar regions of the stratosphere. Those that show mother-of-pearl colors are given the name nacreous. Both these and non-nacreous types are classified alpha-numerically according to their physical state and chemical makeup. Polar mesospheric clouds are the highest in the atmosphere and are given the Latin name noctilucent which refers to their illumination during deep twilight. They are sub-classified alpha-numerically according to specific details of their cirriform physical structure.

Mesospheric, stratospheric, and tropospheric classes are listed on this page in descending order of altitude range. Within the troposphere, families of non-vertical clouds are also listed in descending order of altitude. The genus types within each family are arranged in descending order of average cloud base height. Their constituent species, varieties, and supplementary features are arranged in approximate order of frequency of occurrence. Vertical cloud groups and their constituent genera and species are listed in ascending order of average altitude of cloud tops. Their varieties and supplementary features are arranged in order of approximate frequency of occurrence.

Polar mesospheric class: types and subtypes

Extremely high cirriform

Noctilucent

Noctilucent cloud over Estonia

A thin mostly cirriform-looking cloud based from about 264,000 to 280,000 feet (80–85 km) and occasionally seen in deep twilight after sunset and before sunrise.

Type 1 

Very tenuous resembling cirrus.

Type 2 

Bands — long streaks often in groups parallel or interwoven at small angles.

Subtypes

2A 

Streaks with diffuse, blurred edges.

2B 

Streaks with sharply defined edges.

Type 3

Billows — clearly spaced roughly parallel short streaks.

Subtypes

3A 

Short, straight narrow streaks.

3B 

Wave-like structure with undulations.

Type 4 

Whirls — partial or rarely complete rings with dark centers.

Subtypes

4A 

Whirls of small angular radius of curvature, sometimes resembling light ripples on a water surface.

4B 

Simple curve of medium angular radius with one or more bands.

4C 

Whirls with large scale ring structure.

Polar stratospheric class: types and subtypes

Very high cirriform

Nacreous (mother of pearl) and non-nacreous

Stratospheric nacreous clouds over Antarctica

A thin usually cirriform-looking cloud based from about 60,000 to 100,000 feet (18–30 km) and seen most often between sunset and sunrise.

Type 1 (non-nacreouis) 

Contains supercooled nitric acid and water droplets.

Subtypes

1A 

Crystals of nitric acid and water.

1B 

Additionally contains supercooled sulfuric acid in ternary solution.

Type 2 (nacreous) 

Consists of ice crystals only.

Columnar clouds – rare, column-shaped.

Tropospheric class: families, genera, species, varieties, and supplementary features

High cirriform, stratocumuliform, and stratiform

Genus cirrus

Cirrus spissatus undulatus clouds

Cirrus uncinus clouds

Abbreviation: Ci

Cirrus clouds form in the highest and coldest region of the troposphere from about 16,500 to 40,000 ft (5 to 12 km) in temperate latitudes. At this altitude water almost always freezes so clouds are composed of ice crystals. The clouds tend to be wispy, and are often transparent. Isolated cirrus clouds often do not bring rain, however, large amounts of cirrus clouds can indicate an approaching storm system eventually followed by fair weather.

There are several variations of clouds of the cirrus genus based on species and varieties:

World Meteorological Organization (WMO) species:

• Cirrus fibratus
  High clouds having the traditional "mare's tail" appearance. These clouds are long, fibrous, and curved, with no tufts or curls at the ends.
• Cirrus uncinus
  Filaments with up-turned hooks or curls.
• Cirrus spissatus
  Dense and opaque or mostly opaque patches.
• Cirrus castellanus
  A series of dense lumps, or "towers", connected by a thinner base.
• Cirrus floccus
  Elements which take on a rounded appearance on the top, with the lower part appearing ragged.

WMO varieties; opacity-based:

• None (always translucent).

WMO varieties; fibratus pattern-based:

• Cirrus intortus
  Irregularly curved or tangled filaments.
• Cirrus vertebratus
  Elements arranged in the manner of a vertebrae or fish skeleton.

WMO varieties; fibratus and uncinus pattern-based:

• Cirrus radiatus
  Large horizontal bands that appear to converge at the horizon.
• Cirrus duplicatus
  Sheets at different layers of the upper troposphere, which may be connected at one or more points.
• Varieties are not commonly associated with Ci species spissatus, castellanus, or floccus.

Non-WMO variant:

• Cirrus aviaticus
  Persistent condensation trails (contrails) formed by ice crystals originating from water vapor emitted by aircraft engines.

Genus cirrocumulus

A large field of cirrocumulus stratiformis

Cirrus fibratus radiatus

Abbreviation: Cc

Clouds of the genus cirrocumulus form when moist air at high tropospheric altitude reaches saturation, creating ice crystals. Limited convective instability at the cloud level gives the cloud a rolled or rippled appearance. Despite the lack of a strato- prefix, cirrocumulus is physically more closely related to stratocumulus than the more freely convective cumulus genus.

WMO species:

• Cirrocumulus stratiformis
  Sheets or relatively flat patches of cirrocumulus.
• Cirrocumulus lenticularis
  Lenticular, or lens-shaped high cloud.
• Cirrocumulus castellanus
  Cirrocumulus with "towers", or turrets.
• Cirrocumulus floccus
  Tufts with ragged bases.

WMO varieties; opacity-based:

• None (always translucent)

WMO variety; stratiformis and lenticularis pattern-based:

• Cirrocumulus undulatus
  Undulating base.

WMO variety; stratiformis, castellanus, and floccus pattern-based:

• Cirrocumulus lacunosus
  High cloud with large clear holes.

WMO supplementary features:

• Cirrocumulus mamma
  Bubble-like downward protuberances.
• Cirrocumulus virga
  Light precipitation that evaporates well above ground level.

Genus cirrostratus

Cirrostratus nebulosus merging into darker altostratus translucidus

Abbreviation: Cs

Clouds of the genus cirrostratus consist of mostly continuous, wide sheets of cloud that covers a large area of the sky. It is formed when convectively stable moist air cools to saturation at high altitude, forming ice crystals. Frontal cirrostratus is a precursor to rain or snow if it thickens into mid-level altostratus and eventually nimbostratus as the weather front moves closer to the observer.

WMO species:

• Cirrostratus fibratus
  Cirrostratus sheet with a fibrous appearance, but not as detached as cirrus.
• Cirrostratus nebulosus
  Featureless, uniform sheet.

WMO varieties; opacity-based:

• None (always translucent)

WMO varieties; fibratus pattern-based:

• Cirrostratus duplicatus
  Separate or semi-merged sheets with one layer slightly above the other.
• Cirrostratus undulatus
  Undulating waves.

Varieties are not commonly associated with Cs species nebulosus.

WMO supplementary features:

• No supplementary features.

Middle stratocumuliform and stratiform

Genus altocumulus

Altocumulus floccus

Altocumulus lenticularis duplicatus

Altocumulus castellanus

Altocumulus stratiformis translucidus undulatus

Fallstreak hole -altocumulus stratiformis translucidus lacunosus

Abbreviation: Ac

Clouds of the genus altocumulus are not always associated with a weather front but can still bring precipitation, usually in the form of virga which does not reach the ground. This genus is generally an indicator of limited convective instability at the altitude of its formation from 6,500 to about 23,000 ft (2 to 7 km) in temperate latitudes, and is therefore more closely related to stratocumulus than to the more freely convectice cumulus genus.

WMO species:

• Altocumulus stratiformis
  Sheets or relatively flat patches of altocumulus.
• Altocumulus lenticularis
  Lens-shaped middle cloud. Includes informal variant altocumulus Kelvin–Helmholtz cloud, lenticular spiral indicative of severe turbulence.
• Altocumulus castellanus
  Turreted middle cloud.
• Altocumulus floccus
  Tufted middle clouds with ragged bases.

WMO varieties; stratiformis opacity-based:

• Altocumulus translucidus
  Translucent altocumulus through which the sun or moon can be seen.
• Altocumulus perlucidus
  Opaque middle clouds with translucent breaks.
• Altocumulus opacus
  Opaque altocumulus that obscures the sun or moon.

WMO variety; stratiformis pattern-based:

• Altocumulus radiatus
  Rows that appear to converge at the horizon.

WMO varieties; stratiformis and lenticularis pattern-based:

• Altocumulus duplicatus
  Altocumulus in closely spaced layers, one above the other.
• Altocumulus undulatus
  Altocumulus with wavy undulating base.

WMO variety; stratiformis, castellanus, and floccus pattern-based:

• Altocumulus lacunosus
  Middle cloud with circular holes caused by localized downdrafts.

WMO precipitation-based supplementary feature:

• Altocumulus virga
  Altocumulus producing precipitation that evaporates before reaching the ground.

WMO accessory cloud:

• Altocumulus mamma
  Altocumulus with downward facing bubble-like protuberances caused by localized downdrafts within the cloud.

Genus altostratus

Altostratus translucidus near top of photo merging into altostratus opacus near bottom

Altocumulus stratiformis perlucidus undulatus clouds merging into altostratus opacus, with higher layer of cirrus fibratus

Abbreviation: As

Clouds of the genus altostratus form when a large convectively stable airmass is lifted to condensation in the mid-altitude level of the troposphere, usually along a frontal system. Altostratus can bring light rain or snow. If the precipitation becomes continuous, it may thicken into nimbostratus which can bring precipitation of moderate to heavy intensity.

WMO species:

• No differentiated species (always nebulous).

WMO varieties; opacity-based:

• Altostratus translucidus
  Altostratus through which the sun can be seen.
• Altostratus opacus
  Altostratus that completely blocks out the sun.

WMO varieties; pattern-based:

• Altostratus radiatus
  Bands that appear to converge at the horizon.
• Altostratus duplicatus
  Altostratus in closely spaced layers, one above the other.
• Altostratus undulatus
  Altostratus with wavy undulating base.

WMO precipitation-based supplementary features:

• Altostratus virga
  Accompanied by precipitation that evaporates before reaching the ground.
• Altostratus praecipitatio
  Produces precipitation that reaches the ground.

WMO accessory clouds:

• Altostratus pannus
  Accompanied by ragged lower layer of fractus species clouds forming in precipitation.
• Altostratus mamma
  Altostratus with downward facing bubble-like protuberances caused by localized downdrafts within the cloud.

Low stratocumuliform, stratiform, and cumuliform

Genus stratocumulus

Stratocumulus cumulogenitus with higher layer of altocumulus stratiformis

Stratocumulus castellanus

Abbreviation: Sc

Clouds of the genus stratocumulus are lumpy, often forming in slightly unstable air from near surface to ca. 6,500 feet (2.0 km), and they can produce very light rain or drizzle.

WMO species:

• Stratocumulus stratiformis
  Sheets or relatively flat patches of stratocumulus
• Stratocumulus lenticularis
  Lens-shaped low cloud.
• Stratocumulus castellanus
  Layer of turreted stratocumulus cloud with tower-like formations protruding upwards.

WMO varieties; stratiformis opacity-based:

• Stratocumulus translucidus
  Thin translucent stratocumulus through which the sun or moon can be seen.
• Stratocumulus perlucidus
  Opaque low clouds with translucent breaks.
• Stratocumulus opacus
  Opaque stratocumulus clouds.

WMO variety; stratiformis pattern-based:

• Stratocumulus radiatus
  Low clouds arranged in parallel waves that appear to converge on the horizon.

WMO varieties; stratiformis and lenticularis pattern-based:

• Stratocumulus duplicatus
  Closely spaced layers of low cloud, one above the other.
• Stratocumulus undulatus
  Stratocumulus with wavy undulating base.

WMO variety; stratiformis and castellanus pattern-based:

• Stratocumulus lacunosus
  Low cloud with circular holes caused by localized downdrafts.

WMO precipitation-based supplementary features:

• Stratocumulus virga
  Low cloud producing precipitation that evaporates before reaching the ground.
• Stratocumulus praecipitatio
  Stratocumulus clouds producing precipitation that reaches the ground.

WMO accessory cloud:

• Stratocumulus mamma
  Bubble-like protrusions on the underside.

Genus stratus

At level with stratus nebulosus clouds

Stratus fractus cloud

Abbreviation: St

Clouds of the genus stratus form in low horizontal layers having a ragged or uniform base. Ragged stratus often forms in precipitation while more uniform stratus forms in maritime or other moist stable air mass conditions. The latter often produces drizzle.

WMO species:

• Stratus nebulosus
  Uniform fog-like low cloud.
• Stratus fractus
  Ragged shreds of stratus clouds usually under base of precipitation clouds.

WMO varieties; nebulosus opacity-based:

• Stratus translucidus
  Thin translucent stratus.
• Stratus opacus
  Opaque stratus that obscures the sun or moon.

WMO variety; nebulosus pattern-based:

• Stratus undulatus
  Wavy undulating base.

• Varieties are not commonly associated with St species fractus.

WMO precipitation-based supplementary feature:

• Stratus praecipitatio
  Stratus producing precipitation.

Genus cumulus (little vertical extent)

Abbreviation: Cu

These are fair weather cumuliform clouds of limited convection that do not grow vertically. The vertical height from base to top is generally less than the width of the cloud base. They appear similar to stratocumulus but the elements are generally more detached and less wide at the base.

WMO species

• Cumulus fractus
  Ragged shreds of cumulus clouds.
• Cumulus humilis
  "Fair weather clouds" with flat light grey bases and small white domed tops.

WMO varieties; opacity-based:

• None (always opaque except species fractus which is always translucent).

WMO variety; humilis pattern-based:

• Cumulus radiatus
  Cumulus clouds arranged in parallel lines that appear to converge at the horizon.

WMO supplementary features:

• Not commonly seen with cumulus fractus or humilis.

Vertical cumuliform, stratiform, and cumulonimbiform (low to middle cloud base)

Genus cumulus: Moderate vertical

Cumulus humilis

Cumulus mediocris (from above)

Cumulus mediocris pileus

Cumulus arcus

Abbreviation: Cu

These clouds of moderate vertical development are the product of free convective airmass instability. Continued upward growth suggests showers later in the day. These clouds usually form below 6,500 feet (2.0 km) but can be based as high as 8,000 feet (2.4 km) in temperate climates, and often much higher in arid regions.

WMO species

• Cumulus mediocris

Moderate vertical clouds with flat medium grey bases and higher tops than cumulus humilis.

WMO varieties; opacity-based:

• None (always opaque)

WMO variety; pattern-based:

• Cumulus radiatus
  Cumulus clouds arranged in parallel lines that appear to converge at the horizon.

WMO precipitation-based supplementary features:

• Cumulus virga
  Accompanied by precipitation that evaporates before reaching the ground.
• Cumulus praecipitatio
  Produces precipitation that reaches the ground.

WMO accessory clouds:

• Cumulus pannus
  Accompanied by a lower layer of fractus species cloud forming in precipitation.
• Cumulus mamma
  Downward facing bubble-like protuberances caused by localized downdrafts within the cloud.
• Cumulus pileus
  Small cap-like cloud over parent cumulus cloud.
• Cumulus velum
  A thin horizontal sheet that forms around the middle of a cumulus cloud.
• Cumulus arcus (including roll and shelf clouds)
  Low horizontal cloud formation associated with the leading edge of a thunderstorm outflow.
• Cumulus tuba
  Column hanging from the cloud base which can develop into a small funnel cloud.

Genus nimbostratus: Moderate vertical

Nimbostratus virga

Abbreviation: Ns

Clouds of the genus nimbostratus tend to bring constant precipitation and low visibility. This cloud type normally forms above 6,500 feet (2.0 km) from altostratus cloud but tends to thicken into the lower levels during the occurrence of precipitation. The top of a nimbostratus deck is usually in the middle level of the troposphere.

WMO species:

• No differentiated species (always nebulous).

WMO varieties:

• No varieties (always opaque and never forms in patterns).

WMO precipitation-based supplementary features:

• Nimbostratus virga
  Accompanied by precipitation that evaporates before reaching the ground.
• Nimbostratus praecipitatio
  Produces precipitation that reaches the ground.

WMO accessory cloud:

• Nimbostratus pannus
  Nimbostratus with lower layer of fractus species cloud forming in precipitation.

Genus cumulus: Towering vertical

Abbreviation: Tcu (towering cumulus)

WMO species:

• Cumulus congestus

These large cumulus clouds have flat dark grey bases and very tall tower-like formations with tops mostly in the high level of the troposphere. The International Civil Aviation Organization (ICAO) designates this species as towering cumulus (Tcu).

WMO varieties; opacity-based:

• None (always opaque).

WMO variety; pattern-based:

• Cumulus congestus radiatus
  Towering cumulus arranged in parallel lines that appear to converge at the horizon.

WMO accessory clouds and other supplementary features:

• Supplementary features for cumulus congestus are the same as for smaller cumulus species listed under sub-family of moderate vertical clouds.

Genus cumulonimbus: Towering vertical

Cumulus congestus

Cumulonimbus calvus

Single-cell Cumulonimbus capillatus incus

Abbreviation: Cb

Clouds of the genus cumulonimbus have very dark gray to nearly black flat bases and very high tops that can penetrate the tropopause. They develop from cumulus when the airmass is convectively highly unstable. They generally produce thunderstorms, rain or showers, and sometimes hail, strong outflow winds, and/or tornadoes at ground level.

WMO species:

• Cumulonimbus calvus
  Cumulonimbus with high domed top.
• Cumulonimbus capillatus
  Towering vertical cloud with high cirriform top.

WMO varieties:

• No varieties (always opaque and never forms in patterns).

WMO precipitation-based supplementary features:

• Cumulonimbus virga
  Accompanied by precipitation that evaporates before reaching the ground.
• Cumulonimbus praecipitatio
  Cumulonimbus producing precipitation that reaches the ground.

WMO accessory clouds:

• Cumulonimbus pannus
  Accompanied by a lower layer of fractus species cloud forming in precipitation.
• Cumulonimbus incus
  Cumulonimbus with flat anvil-like cirriform top caused by wind shear where the rising air currents hit the inversion layer at the tropopause.
• Cumulonimbus mamma
  Mammatus consisting of bubble-like protrusions on the underside caused by localized downdrafts.
• Cumulonimbus pileus
  Small cap-like cloud over parent cumulonimbus.
• Cumulonimbus velum
  A thin horizontal sheet that forms around the middle of a cumulonimbus.
• Cumulonimbus arcus (including roll and shelf clouds)
  Low, horizontal cloud formation associated with the leading edge of thunderstorm outflow.
• Cumulonimbus tuba
  Column hanging from the cloud base which can develop into a funnel cloud or tornado.

Non-WMO informal term:

• Hot tower
  A tropical cumulonimbus cloud that penetrates the tropopause.

Alphabetical list of WMO tropospheric genera

Latin etymologies

• Altocumulus – altus and cumulus – high heap; now applied to middle stratocumuliform.
• Altostratus – altus and stratus – high sheet; now applied to middle stratiform.
• Cirrocumulus – cirrus and cumulus – thin, wispy heap; applied to high stratocumuliform.
• Cirrostratus – cirrus and stratus – thin, wispy sheet; applied to high stratiform.
• Cirrus – thin and wispy; applied to high cirriform.
• Cumulonimbus – cumulus and nimbus (Latin for "raincloud") – precipitation-bearing heap; applied to vertical cumulonimbiform.
• Cumulus – Latin for "heap"; applied to low or vertical cumuliform.
• Nimbostratus – nimbus and stratus – precipitation-bearing sheet; applied to deep stratiform with vertical extent.
• Stratocumulus – stratus and cumulus – heap partly spread into a sheet; applied to low stratocumuliform.
• Stratus – Latin for "sheet"; applied to low mostly shallow stratiform.

Alphabetical list WMO tropospheric species

• Castellanus – castle-like with a series of turret shapes – indicates air mass instability.
• Congestus – great verticsal development and heaped into cauliflower shapes – indicates considerable airmass instability and strong upcurrents.
• Fibratus – thin filament type clouds, can be straight or slightly curved.
• Floccus – looking like a tuft of wool – indicates some mid and/or high level instability.
• Fractus – irregular shredded appearance – forms in precipitation and/or gusty winds.
• Humilis – small, low, flattened cumulus – indicates relatively slight airmass instability.
• Lenticularis – having a lens-like appearance – formed by standing waves of wind passing over mountains or hills.
• Mediocris – medium size cumulus with bulges at the top – indicates moderate instability and upcurrents.
• Nebulosus – indistinct cloud without features – indicates light wind if any and stable air mass.
• Spissatus – thick cirrus with a grey appearance – indicates some upward movement of air in the upper troposphere.
• Stratiformis – horizontal cloud sheet of flattened cumuliform cloud – indicates very slight airmass instability.
• Uncinus – cirrus with a hook shape at the top – indicates a nearby backside of a weather system.

Alphabetical list of tropospheric varieties, supplementary features, and processes of formation

A translucent wave cloud -altocumulus lenticularis

WMO terms

• Arcus – arch or a bow – mostly attached to cumulus, thick with ragged edges.
• Cumulogenitus – formed by the spreading out of cumulus clouds.
• Cumulonimbogenitus – formed by the spreading out of cumulonimbus clouds.
• Duplicatus – double – partly merged layers of cloud.
• Incus – anvil – top part of Cb cloud, anvil-shaped.
• Intortus – twisted – curved and tangled cirrus.

Mammatus over Squaw Valley

• Mammatus (WMO term mamma) – breast cloud – round pouches on under-surface of cloud.
• Lacunosus – full of holes – thin cloud distinguished by holes (sometimes known as fallstreak holes) and ragged edges.
• Opacus – thick and shadowy – an opaque sheet of cloud.
• Pannus – shredded cloth – shredded sections attached to main cloud.
• Perlucidus – translucent – sheet of cloud with small spaces between elements.
• Pileus – capped – hood-shaped cumulus cloud.
• Praecipitatio – falling – cloud whose precipitation reaches the ground.
• Radiatus – radiant – clouds in parallel lines converging at a central point near the horizon.
• Tuba – shaped like a tuba – column hanging from the bottom of cumulus.
• Translucidus – transparent – translucent patch or sheet.
• Undulatus – wavy – cloud displaying an undulating pattern.
• Velum – a ship's sail – sail-like in appearance.
• Vertebratus – skeletal and bone-like – cirrus arranged to look like bones, a skeleton or calcium.

Informal terms

• Fallstreak hole – see lacunosus.
• Pyrocumulus – cumulus clouds formed by quickly generated ground heat; including forest fires, volcanic eruptions and low level nuclear detonation, generally of the WMO species mediocris or congestus.

Alphabetical list of WMO and other tropospheric storm associated genera, species, varieties, and supplementary features

• Accessory cloud (WMO term supplementary feature) – cloud that is attached to and develops on body of main cloud.
• Anvil (WMO supplementary feature incus) – the top flatter part of a cumulonimbus cloud.
• Anvil dome (WMO supplementary feature incus) – the overshooting top on a Cb that is often present on a supercell.
• Anvil rollover – (slang) circular protrusion attached to underside of anvil.
• Arcus cloud (WMO supplementary feature) – arch or a bow shape, attached to cumulus, thick with ragged edges.
• Backsheared anvil – (slang) anvil that spreads upwind, indicative of extreme weather.
• Clear slot or dry slot (informal term) – an evaporation of clouds as a rear flank downdraft descends and dries out cloud and occludes around a mesocyclone.
• Cloud tags (WMO species fractus) – ragged detached portions of cloud.
• Collar cloud (WMO supplementary feature velum) – ring shape surrounding upper part of wall cloud.
• Condensation funnel (informal term) – the cloud of a funnel cloud aloft or a tornado.
• Altocumulus castellanus (WMO genus and species) – castle crenellation-shaped altocumulus clouds.
• Cumulus (WMO genus) – heaped clouds.
• Cumulus castellanus – (informal variation of WMO genus and species cumulus congestus) cumulus with tops shaped like castle crenellations.
• Cumulus congestus (WMO genus and species) – considerable vertical development and heaped into cauliflower shapes.
• Cumulus fractus (WMO genus and species) – ragged detached portions of cumulus cloud.
• Cumulus humilis (WMO genus and species) – small, low, flattened cumulus, early development.
• Cumulus mediocris (WMO genus and species) – medium-sized cumulus with bulges at the top.
• Cumulus pileus (WMO genus and supplementary feature) – capped, hood-shaped cumulus cloud.
• Cumulus praecipitatio (WMO genus and supplementary feature) – cumulus whose precipitation reaches the ground.
• Cumulus radiatus (WMO genus and variety) – cumulus arranged in parallel lines that appear to converge near the horizon.
• Cumulus tuba (WMO genus and supplementary feature) – column hanging from the bottom of cumulus.
• Cumulus undulatus (WMO genus and variety) – cumulus displaying an undulating pattern.
• Cumulonimbus (WMO genus) – heaped towering rain-bearing clouds that stretch to the upper levels of the troposphere.
• Cumulonimbus calvus (WMO genus and species) – cumulonimbus with round tops like cumulus congestus.
• Cumulonimbus capillatus (WMO genus and species) – Cb with cirriform top.
• Cumulonimbus incus (WMO genus and supplementary feature) – Cb with anvil top.
• Cumulonimbus mamma (WMO genus and supplementary feature) – Cb with pouch-like protrusions that hang from under anvil or cloud base.
• Cumulonimbus pannus (WMO genus and supplementary feature) – shredded sections attached to main Cb cloud.
• Cumulonimbus pileus (WMO genus and supplementary feature) – capped, hood-shaped cumulonimbus cloud.
• Cumulonimbus praecipitatio (WMO genus and supplementary feature) – Cb whose precipitation reaches the ground.
• Cumulonimbus tuba (WMO genus and supplementary feature) – column hanging from the bottom of cumulonimbus.
• Debris cloud (informal term) – rotating "cloud" of debris found at base of tornado.
• Hail fog (informal term) – a shallow surface layer of fog that sometimes forms in vicinity of deep hail accumulation, can be very dense.
• Inflow band (informal term) – a laminar band marking inflow to a Cb, can occur at lower or mid levels of the cloud.
• Inverted cumulus (informal variation of WMO supplementary feature mamma) – cumulus which has transferred momentum from an exceptionally intense Cb tower and is convectively growing on the underside of an anvil.
• Funnel cloud (informal term) – rotating funnel of cloud hanging from under Cb, not making contact with ground.
• Knuckles (informal variation of WMO supplementary feature mamma) – lumpy protrusion that hangs from edge or underside of anvil.

Cumulus arcus roll cloud over Wisconsin

• Roll cloud (may be informal term for WMO genus stratocumulus or supplementary feature arcus) – elongated, low-level, tube shaped, horizontal cloud.
• Rope – (slang) narrow, sometimes twisted funnel type cloud seen after a tornado dissipates.
• Rope cloud (informal term) – A narrow, long, elongated lines of cumulus cloud formation that develop at the leading edge of an advancing cold front or weather fronts that is often visible in satellite imagery.
• Scud cloud (informal term for WMO species fractus) – ragged detached portions of cloud.
• Shelf cloud (informal term for WMO supplementary feature arcus) – wedge-shaped cloud often attached to the underside of Cb.
• Stratus fractus (WMO genus and species) – ragged detached portions of stratus cloud.
• Striations (informal term for WMO supplementary feature velum) – a groove or band of clouds encircling an updraft tower, indicative of rotation.
• Tail cloud (informal term) – an area of condensation consisting of laminar band and cloud tags extending from a wall cloud towards a precipitation core.
• Towering cumulus (TCu) (aviation term for WMO genus and species cumulus congestus) – a large cumulus cloud with great vertical development, usually with a cauliflower-like appearance, but lacking the characteristic anvil of a Cb.
• Wall cloud (informal term) – distinctive fairly large lowering of the rain-free base of a Cb, often rotating.

Other planets

Venus

Thick overcast mostly stratiform clouds of sulfur dioxide that obscure the planet's surface.

Mars

High thin scattered mostly cirriform clouds of water ice through which the planet's surface can be seen. Morning fog of water and/or carbon dioxide commonly forms in low areas of the planet. There is also a polar cap cloud over the winter pole which is mostly suspended frozen carbon dioxide.

Jupiter and Saturn

Overcast mostly stratiform cloud decks in parallel latitudinal bands at the tropopause alternatingly composed of ammonia crystals and ammonium hydrosulfate. Lower layer with some cumuliform water cloud can create thunderstorms.

Uranus and Neptune

Clouds layers made mostly of methane gas.

External links

• http://nephology.eu International Cloud Atlas online

• Cloud Classification (National Weather Service)
• Skywatcher Chart (National Weather Service)
• S'COOL Cloud Types Tutorial
• Cloud Appreciation Society
• Texas A&M Cloud Glossary
• Cloud-identification site
• UK Met Office cloud classification page
• Cloud Atlas (Atlas Chmur) (in Polish)
• NOAA