List of cloud types

Clouds are formed in Earth's atmosphere when water evaporates into vapor from oceans, lakes, and ponds or by evapotranspiration 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 can be divided into three main categories with names based on 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. The other two categories are stratiform with clouds that are mostly sheet-like in structure, and cumuliform that appear heaped, rolled, and/or rippled.[1]

In the troposphere, nine of the ten genus types are derived by cross-classifying the three categories into four families defined by altitude range; high, middle, low, and moderate vertical. Each of these families includes one stratiform and one cumuliform genus. Cirriform clouds differ in that they are only found in the high altitude family as a third member, and therefore only constitute a single genus cirrus. High stratiform and cumuliform clouds carry the prefix cirro which yield the genera cirrostratus and cirrocumulus. Middle cloud genera have the prefix alto (altostratus and altocumulus) to distinguish them from the high clouds, while low altitude stratiform and cumuliform genera (stratus and stratocumulus) carry no height-related prefixes. The fourth family comprises stratiform and cumuliform genera of moderate vertical extent (nimbostratus and cumulus) that form in the low or middle altitude range. This group also has no height-related prefixes, but its stratiform genus carries the prefix nimbo to denote its ability to produce widespread precipitation.

A fifth family or sub-family of towering vertical clouds comprises only cumuliform types. One is cumulonimbus, the tenth genus type, and the other is cumulus congestus, a towering species of the genus cumulus whose other species belong to the family of moderate vertical clouds. All cloud genera except nimbostratus are divided into species and/or varieties based on specific physical characteristics of the clouds, but the cumulus genus is the only one that has species in two different altitude families.[2][3]

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 are 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. They are given the name Nacreous due to the mother-of-pearl colors that are typically seen, and are sub-classified alpha-numerically according to their 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.

Contents

Troposphere: genera, species, varieties, and supplementary features

High: base ca. 16,500 to ca. 40,000 ft /5 to 12  km in temperate latitudes

Genus cirrus

Cirrus clouds
Cirrus uncinus clouds

Abbreviation: Ci

Cirrus clouds form in the highest and coldest region of the troposphere. 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:

WMO species

Cirrus clouds having the traditional "mare's tail" appearance. These clouds are long, fibrous, and curved, with no tufts or curls at the ends.
Cirrus filaments with up-turned hooks or curls.
Cirrus in the form of dense and opaque or mostly opaque patches.
A series of dense lumps, or "towers" of cirrus, connected by a thinner base.
Cirrus with elements which take on a rounded appearance on the top, with the lower part appearing ragged.
Cirrus with elements arranged in the manner of a vertebrae or fish skeleton.

WMO varieties

  • Cirrus undulatus
Undulating cirrus.
Sheets of cirrus at different layers of the atmosphere, which may be connected at one or more points.
Cirrus clouds whose filaments are irregularly curved or tangled.
Large area of cirrus displaying horizontal bands that appear to converge at the horizon.

Non-WMO variant

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

Genus cirrocumulus

Cirrocumulus stratiformis
Cirrocumulus undulatus

Abbreviation: Cc[4]

Clouds of the genus cirrocumulus form when moist air at a high 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.[5]

WMO species

Cirrocumulus with "towers", or turrets.
Cirrocumulus in the form of tufts with ragged bases.
Lenticular, or lens-shaped cirrocumulus.
Sheets or relatively flat patches of cirrocumulus.

WMO varieties

undulating cirrocumulus.
Cirrocumulus with large clear holes.

WMO supplementary features

  • Cirrocumulus mamma
Cirrocumulus with bubble-like downward protuberances.
  • Cirrocumulus virga
Cirrocumulus producing light precipitation that evaporates well above ground level.

Genus cirrostratus

Cirrostratus

Abbreviation: Cs[4]

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 a high altitude, forming ice crystals.[7] 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 sheet with a fibrous appearance, but not as detached as cirrus.
Featureless, uniform cirrostratus.

WMO varieties

  • Cirrostratus duplicatus[8]
separate or semi-merged sheets of cirrostratus with one layer slightly above the other.
  • Cirrostratus undulatus[8]
Cirrostratus in undulating waves.

WMO supplementary features -none

Middle: base ca. 6,500 to ca. 23,000 ft /2 to 7  km in temperate latitudes

Genus altocumulus

Altocumulus
Altocumulus lenticularis
Altocumulus castellanus
Altocumulus undulatus

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, and is therefore more closely related to stratocumulus than to the more freely convectice cumulus genus.

WMO species

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

WMO varieties

  • Altocumulus lacunosus
Altocumulus with circular holes caused by localized downdrafts.
  • Altocumulus duplicatus
Altocumulus in closely spaced layers, one above the other.
  • altocumulus opacus
Opaque altocumulus that obscures the sun or moon.
  • Altocumulus translucidus
Translucent altocumulus through which the sun or moon can be seen.
  • Altocumulus perlucidus
Opaque altocumulus with translucent breaks.
  • Altocumulus radiatus
Altocumulus in rows that appear to converge at the horizon.
  • Altocumulus undulatus
Altocumulus with wavy undulating base.

WMO supplementary features

  • Altocumulus mamma
Altocumulus with downward facing bubble-like protuberances caused by localized downdrafts within the cloud.
  • Altocumulus virga
Altocumulus producing precipitation that evaporates before reaching the ground.

Genus altostratus

Altostratus
Cirrus and Altostratus undulatus clouds

Abbreviation: As

Clouds of the genus altostratus form when a large convectively stable airmass is lifted to condensation altitude, usually along a frontal system, and can bring rain or snow. If the precipitation becomes continuous, it may thicken into nimbostratus.

WMO species

  • No differentiated species.

WMO varieties

  • Altostratus opacus
Altostratus that completely blocks out the sun.
  • Altostratus translucidus
Altostratus through which the sun can be seen.
  • Altostratus duplicatus
Altostratus in closely spaced layers, one above the other.
  • Altostratus radiatus
Altostratus in bands that appear to converge at the horizon.
  • Altostratus undulatus
Altostratus with wavy undulating base.

WMO supplementary features

  • Altostratus mamma
Altostratus with downward facing bubble-like protuberances caused by localized downdrafts within the cloud.
  • Altostratus virga
Altostratus producing precipitation that evaporates before reaching the ground.
  • Altostratus praecipitatio
Altostratus producing precipitation that reaches the ground.
  • Altostratus pannus
Altostratus with ragged lower layer of fractus species clouds forming in precipitation.

Low: base near surface to ca. 6,500 ft /2  km in temperate latitudes

Genus stratocumulus

Stratocumulus cumulogenitus
Stratocumulus castellanus

Abbreviation: Sc

Clouds of the genus stratocumulus are lumpy, often forming in slightly unstable air following a cold front, and they can produce very light rain or drizzle.

WMO species

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

WMO varieties

  • Stratocumulus lacunosus
Stratocumulus with circular holes caused by localized downdrafts.
  • Stratocumulus duplicatus
Closely spaced layers of stratocumulus, one above the other.
  • stratocumulus opacus
Opaque stratocumulus clouds.
  • stratocumulus perlucidus
Opaque stratocumulus clouds with translucent breaks.
  • Stratocumulus radiatus
Stratocumulus clouds arranged in parallel waves that appear to converge on the horizon.
  • stratocumulus translucidus
Thin translucent stratocumulus through which the sun or moon can be seen.
  • Stratocumulus undulatus
Stratocumulus with wavy undulating base.

WMO supplementary features

  • Stratocumulus mamma
Stratocumulus with bubble-like protrusions on the underside.
  • Stratocumulus virga
Stratocumulus producing producing precipitation that evaporates before reaching the ground.
  • Stratocumulus praecipitatio
Stratocumulus clouds producing precipitation that reaches the ground.

Genus stratus

At level with some stratus 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 fractus
Ragged shreds of stratus clouds usually under base of precipitation clouds.
  • Stratus nebulosus
Uniform fog-like stratus.

WMO varieties

  • Stratus opacus
Opaque stratus that obscures the sun or moon.
  • Stratus translucidus
Thin translucent stratus.
  • Stratus undulatus
Stratus with wavy undulating base.

WMO supplementary features - none

Moderate vertical: low to middle base from near surface to ca. 10,000 ft /3  km; tops mostly middle level

Genus nimbostratus

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 from altostratus cloud but can thicken into the lower levels during the occurrence of precipitation.

WMO species

  • No differentiated species.

WMO varieties

  • No varieties.

WMO supplementary features

  • Nimbostratus pannus
Nimbostratus with lower layer of fractus species cloud forming in precipitation.
  • Nimbostratus praecipitatio
Nimbostratus producing precipitation that reaches the ground.
Nimbostratus producing precipitation that evaporates before reaching the ground.

Genus cumulus

Abbreviation: Cu

Cumulus humilis
Cumulus mediocris (from above)
Cumulus pileus

Small clouds of the genus cumulus are often associated with fair weather. However, they are the product of free convective airmass instability and can grow into more storm-like towering vertical buildups including cumulonimbus. Continued upward growth suggests showers later in the day. These clouds usually form below 6,500 feet but can be based as high as 10,000 feet under conditions of very low relative humidity.

WMO species

  • Cumulus fractus
Ragged shreds of cumulus clouds.
"Fair weather clouds" with flat light grey bases and small white domed tops.
Cumulus clouds with flat medium grey bases and higher tops than cumulus humilis.
Large cumulus clouds with flat dark grey bases and very tall tower-like formations. Also known informally as towering cumulus (TCU), especially in aviation circles.

WMO varieties

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

WMO supplementary features

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

Towering vertical: low to middle base from near surface to ca. 10,000 ft /3  km; tops mostly high level

Genus cumulonimbus

Cumulonimbus calvus
Single-cell Cumulonimbus incus
Cumulus congestus
Arcus

Abbreviation: Cb

Clouds of the genus cumulonimbus have very dark grey to nearly black flat bases and extremely high tops. 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 tornados at ground level.

WMO species

Cumulonimbus with high domed top.
  • Cumulonimbus capillatus
Cumulonimbus with high cirriform top.

WMO Varieties -none

WMO supplementary features

Cumulonimbus with flat anvil-like cirriform top caused by wind shear where the rising air currents hit the inversion layer at the tropopause.
  • Cumulonimbus pileus
Small cap-like cloud over parent cumulonimbus cloud.
  • Cumulonimbus mamma
Cumulonimbus with mammatus consisting of bubble-like protrusions on the underside caused by localized downdrafts.
  • Cumulonimbus arcus (including roll and shelf clouds)
Low, horizontal cloud formation associated with the leading edge of thunderstorm outflow.
  • Cumulonimbus virga
Cumulonimbus producing precipitation that evaporates before reaching the ground.
  • Cumulonimbus praecipitatio
Cumulonimbus clouds producing precipitation that reaches the ground.
  • Cumulonimbus tuba
Column hanging from the bottom of cumulonimbus cloud.
  • Cumulonimbus velum
Cumulonimbus with a thin horizontal sheet that forms around the middle.
  • Cumulonimbus pannus
Cumulonimbus with lower layer of fractus species cloud forming in precipitation.

Non-WMO informal term:

A tropical cumulonimbus cloud that penetrates the tropopause.

Above the troposphere: types and sub-types

Polar stratospheric (very high): base ca. 60,000 to ca. 100,000 ft /19 to 29 km

Nacreous (mother of pearl)

Stratospheric nacreous clouds over Antarctica

A thin usually cirriform-looking cloud seen most often between sunset and sunrise.

  • Type 1

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

Consists of ice crystals only.

Columnar Clouds - rare, column-shaped.

Polar mesospheric (extremely high): base ca. 165,000 to ca. 185,000 ft /51 to 56 km

Noctilucent

Noctilucent cloud over Estonia

A thin mostly cirriform-looking cloud seen most often 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 speaced 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 centres.

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.

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.

The meaning of tropospheric names

WMO stems and prefixes

  • Altus/alto – high in original meaning, but now applied to middle clouds.
  • Cirrus/cirro – wispy, -applied to high clouds.
  • Cumulus/cumulo – puffy, from Latin for stack.
  • Nimbus/nimbo – precipitation-bearing (Latin for "raincloud")
  • Stratus/strato – flat layer (Latin for "sheet").

Etymology of WMO genera

  • Altocumulus – altus and cumulus – high (middle) heap.
  • Altostratus – altus and stratus – high (middle) flat layer.
  • Cirrocumulus – cirrus and cumulus – thin, wispy and puffy.
  • Cirrostratus – cirrus and stratus – thin, wispy and spread into flat layer.
  • Cirrus – thin and wispy.
  • Cumulonimbus – cumulus and nimbus – rain-bearing heap. The cumulonimbus cloud can cause thunderstorms and tornados.
  • Cumulus – puffy.
  • Nimbostratus - nimbus and stratus - rain-bearing layer.
  • Stratocumulus, (Cumulostratus) - stratus and cumulus - heap spread into flat layer.
  • Stratus - flat layer.

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.
  • Lenticular cloud – 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
Fallstreak hole

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 – like a trumpet – 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 informal 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 uncus) - 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 species amd 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.
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 very narrow, long, sometimes meandering, cumulus cloud formation that is frequently 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.

Notes and references

  1. ^ NOAA
  2. ^ WMO International Cloud Atlas
  3. ^ "Definition of nimbus". Numen - The Latin Lexicon. http://latinlexicon.org/definition.php?p1=1010530. Retrieved 4 August 2011. 
  4. ^ a b Dunlop, Storm (2003-6-1). The Weather Identification Handbook, p.9. The Lyons Press; 1st edition, Guilford, CT. ISBN 1585748479.
  5. ^ Burroughs, William James; Crowder, Bob (January 2007). Weather, p.216. Fog City Press, San Francisco. ISBN 9781740895798.
  6. ^ a b c d e f Dunlop, Storm (2003-6-1). The Weather Identification Handbook, p.66-67. The Lyons Press; 1st edition, Guilford, CT. ISBN 1585748479.
  7. ^ Burroughs, William James; Crowder, Bob (January 2007). Weather, p.215. Fog City Press, San Francisco. ISBN 9781740895798.
  8. ^ a b c d Dunlop, Storm (2003-6-1). The Weather Identification Handbook, p.62-63. The Lyons Press; 1st edition, Guilford, CT. ISBN 1585748479.

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