List of cloud types


The list of cloud types groups the main genera as high, middle, multi-level, and low according to the altitude level or levels at which each cloud is normally found. Small cumulus are commonly grouped with the low clouds because they do not show significant vertical extent. Of the multi-level genus-types, those with the greatest convective activity are often grouped separately as towering vertical. The genus types all have Latin names.
The genera are also grouped into five physical forms. These are, in approximate ascending order of instability or convective activity: stratiform sheets; cirriform wisps and patches; stratocumuliform patches, rolls, and ripples; cumuliform heaps, and cumulonimbiform towers that often have complex structures. Most genera are divided into species with Latin names, some of which are common to more than one genus. Most genera and species can be subdivided into varieties, also with Latin names, some of which are common to more than one genus or species. 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. Very low stratiform clouds that touch the Earth's surface are given the common names, fog and mist, which are not included with the Latin nomenclature of clouds that form aloft in the troposphere.
Above the troposphere, stratospheric and mesospheric clouds have their own classifications with common names for the major types and alpha-numeric nomenclature for the subtypes. They are characterized by altitude as very high level and extreme level. Three of the five physical forms in the troposphere are also seen at these higher levels, stratiform, cirriform, and stratocumuliform, although the tops of very large cumulonimbiform clouds can penetrate the lower stratosphere.

Cloud identification and classification: Order of listed types

In section two of this page, height ranges are sorted in approximate descending order of altitude expressed in general terms. On the cross-classification table, forms and genus types are shown from left to right in approximate ascending order of instability.
In sections three to five, terrestrial clouds are listed in descending order of the altitude range of each atmospheric layer in which clouds can form:
In section six, the cloud types in the general lists and the mother clouds in the applicable classification table are sorted in alphabetical order except where noted. The species table shows these types sorted from left to right in approximate ascending order of the convective instability of each species. The table for supplementary features has them arranged in approximate descending order of frequency of occurrence.
In section seven, extraterrestrial clouds can be found in the atmospheres of other planets in our solar system and beyond. The planets with clouds are listed in order of their distance from the sun, and the clouds on each planet are in approximate descending order of altitude.

Cloud identification and classification throughout the homosphere

The table that follows is very broad in scope and draws from several methods of classification, both formal and informal, used in different levels of the homosphere by a number of authorities. Homospheric types are cross-classified as a whole by form and level to derive the ten tropospheric genera, the fog and mist that forms at surface level, and several additional major types above the troposphere. The cumulus genus includes four species as defined by vertical size and structure. It should therefore be seen as an illustration of how the various cloud types are related to each other at all altitudes from surface-level to the "edge of space", rather than as a strict classification per se.
Level/Form Stratiform
non-convective		 Cirriform
mostly non-convective		 Stratocumuliform
limited-convective		 Cumuliform
free-convective		 Cumulonimbiform
strong-convective
Extreme-levelPMC: Noctilucent veilsNoctilucent billows or whirlsNoctilucent bands
Very high-levelNitric acid & water PSCCirriform nacreous PSCLenticular nacreous PSC
High-levelCirrostratusCirrusCirrocumulus
Mid-levelAltostratusAltocumulus
Towering verticalCumulus congestusCumulonimbus
Multi-level or moderate verticalNimbostratusCumulus mediocris
Low-levelStratusStratocumulusCumulus humilis or fractus
Surface-levelFog or mist

Polar mesospheric cloud identification and classification

Clouds that form in the mesosphere have a generally cirriform structure, but are not given Latin names based on that characteristic. 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.

Extreme-level stratiform, stratocumuliform, and cirriform

s are thin clouds that come in a variety of forms based from about and occasionally seen in deep twilight after sunset and before sunrise.
;Type 1 : Veils, very tenuous stratiform; resembles cirrostratus or poorly defined cirrus.
;Type 2 : Long stratocumuliform bands, often in parallel groups or interwoven at small angles. More widely spaced than cirrocumulus bands.
;Type 3: Billows. Clearly spaced, fibrous cirriform, roughly parallel short streaks.
;Type 4 : Whirls. Partial cirriform rings with dark centers.

Polar stratospheric cloud identification and classification

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.

Very high-level stratiform

;Nitric acid and water polar stratospheric : Sometimes known as type 1, a thin sheet-like cloud resembling cirrostratus or haze. Contains supercooled nitric acid and water droplets; sometimes also contains supercooled sulfuric acid in ternary solution.

Very high-level cirriform and stratocumuliform

;Nacreous polar stratospheric cloud : Sometimes known as type 2, a thin usually cirriform or lenticular looking cloud based from about and seen most often between sunset and sunrise. Consists of ice crystals only.

Cloud identification and classification in the troposphere

Tropospheric clouds are divided into physical forms defined by structure, and levels defined by altitude range. These divisions are cross-classified to produce ten basic genus-types. They have Latin names as authorized by the World Meteorological Organization that indicate physical structure, altitude or étage, and process of formation

High-level cirriform, stratocumuliform, and stratiform

High clouds form in the highest and coldest region of the troposphere from about 5 to 12 km in temperate latitudes. At this altitude water almost always freezes so high clouds are generally composed of ice crystals or supercooled water droplets.

Genus cirrus

Abbreviation: Ci
Cirriform clouds tend to be wispy and are mostly transparent or translucent. Isolated cirrus do not bring rain; however, large amounts of cirrus 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:
Species
High clouds having the traditional "mare's tail" appearance. These clouds are long, fibrous, and curved, with no tufts or curls at the ends.
Filaments with up-turned hooks or curls.
Dense and opaque or mostly opaque patches.
A series of dense lumps, or "towers", connected by a thinner base.
Elements which take on a rounded appearance on the top, with the lower part appearing ragged.

Genus cirrocumulus

Abbreviation: Cc.
High-level stratocumuliform clouds of the genus cirrocumulus form when moist air at high tropospheric altitude reaches saturation, creating ice crystals or supercooled water droplets. Limited convective instability at the cloud level gives the cloud a rolled or rippled appearance. Despite the lack of a strato- prefix, layered cirrocumulus is physically a high stratocumuliform genus.
High stratocumuliform species
Sheets or relatively flat patches of cirrocumulus.
Lenticular, or lens-shaped high cloud.
Cirrocumulus layer with "towers", or turrets joined at the bases.
Very small white heaps with ragged bases and rounded tops.

Genus cirrostratus

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.
Species
Cirrostratus sheet with a fibrous appearance, but not as detached as cirrus.
Featureless, uniform sheet.

Mid-level stratocumuliform and stratiform

Middle cloud forms from 2 to 7 km in temperate latitudes, and may be composed of water droplets or ice crystals depending on the temperature profile at that altitude range.

Genus altocumulus

Abbreviation: Ac
Mid-level stratocumuliform 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. Layered forms of altocumulus are generally an indicator of limited convective instability, and are therefore mainly stratocumuliform in structure.
Mid-level stratocumuliform species
Sheets or relatively flat patches of altocumulus.
Lens-shaped middle cloud. Includes informal variant altocumulus Kelvin–Helmholtz cloud, lenticular spiral indicative of severe turbulence.
Turreted layer cloud.
Tufted stratocumuliform clouds with ragged bases.

Genus altostratus

Abbreviation: As
Stratiform clouds of the genus altostratus form when a large convectively stable airmass is lifted to condensation in the middle 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.
Species
Clouds with upward-growing vertical development usually form below, but can be based as high as in temperate climates, and often much higher in arid regions.

Genus cumulonimbus: Towering vertical

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.
Species
Cumulonimbus with high domed top.
Towering vertical cloud with high cirriform top.

Genus cumulus: Towering vertical

Abbreviations: Cu con or Tcu
Species

Genus nimbostratus: Multi-level

Abbreviation: Ns
Clouds of the genus nimbostratus tend to bring constant precipitation and low visibility. This cloud type normally forms above 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.
Species
Abbreviation: Cu
Moderate vertical cumulus is the product of free convective airmass instability. Continued upward growth suggests showers later in the day.
Species
Low cloud forms from near surface to ca. and are generally composed of water droplets.

Genus stratocumulus

Abbreviation: Sc
Clouds of the genus stratocumulus are lumpy, often forming in slightly unstable air, and they can produce very light rain or drizzle.
Species
Sheets or relatively flat patches of stratocumulus
Lens-shaped low cloud.
Elongated, low-level, tube shaped, horizontal stratocumuliform cloud.
Scattered or isolated stratocumulus tufts with domed tops and ragged bases.
Layer of turreted stratocumulus cloud with tower-like formations protruding upwards.

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.
Species
Ragged shreds of cumulus clouds.
"Fair weather clouds" with flat light grey bases and small white domed tops.

Genus stratus

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. Stratus that touches the Earth's surface is given the common name, fog, rather than a Latin name that applies only to clouds that form and remain aloft in the troposphere.
Species
Uniform fog-like low cloud.
Ragged shreds of stratus clouds usually under base of precipitation clouds.

Tropospheric cloud types with Latin etymologies where applicable

Cloud types are sorted in alphabetical order except where noted.

WMO genera

The division of genus types into species is as shown in the following table. The species are sorted from left to right in approximate ascending order of instability or vertical extent. =Stratiform types, =Cirriform types, =Stratocumuliform types, =Cumuliform types, =Cumulonimbiform types. The genus types are arranged from top to bottom in the left column in approximate descending order of average overall altitude range.

WMO varieties

Opacity-based
Pattern-based
The following table shows the cloud varieties arranged across the top of the chart from left to right in approximate descending order of frequency of appearance. The genus types associated with each variety are sorted from top to bottom in approximate descending order of average overall altitude range. Where applicable, the genera and varieties are cross-classified to show the species normally associated with each combination of genus and variety. The exceptions include altostratus that has varieties but no species, towering cumulus and cumulonimbus that have species but no varieties, and nimbostratus has no species or varieties.

WMO supplementary features

Precipitation-based supplementary features
Cloud-based supplementary features
Accessory clouds
The supplementary features are associated with particular genera as follows. They are sorted from left to right in approximate decreasing order of frequency of occurrence for each of three categories. The genus types are arranged from top to bottom in approximate descending order of average overall altitude range.

Genitus mother clouds

The possible combinations of genera and mother clouds can be seen in this table. The genitus and mutatus clouds are each sorted from left to right in alphabetical order. The genus types are arranged from top to bottom in approximate descending order of average overall altitude range.

Informal terms recently accepted for WMO classification with Latin nomenclature

[Venus]

Thick overcast clouds of sulfur dioxide and carbon dioxide in three main layers at altitudes of 45 to 65 km that obscure the planet's surface and can produce virga.

Stratiform

Overcast opaque clouds sheets.

Stratocumuliform

Wave clouds with clear gaps through which lower stratiform layers may be seen.

Cumuliform and cumulonimbiform

Embedded convective cells that can produce lightning.

[Mars]

Clouds resembling several terrestrial types can be seen over Mars and are believed to be composed of water-ice.

Extremely high cirriform

Noctilucent clouds are known to form near the poles at altitudes similar to or higher than the same type of clouds over Earth.

High cirriform

Thin scattered wispy cloud resembling cirrus through which the planet's surface can be seen.

High stratocumuliform

Thin scattered wave-cloud resembling cirrocumulus.

Low stratocumuliform

Wave-cloud resembling stratocumulus, especially as a polar cap cloud over the winter pole which is mostly composed of suspended frozen carbon dioxide.

Surface-based

Morning fog of water and/or carbon dioxide commonly forms in low areas of the planet.

[Jupiter] and [Saturn]

Cloud decks in parallel latitudinal bands at and below the tropopause alternatingly composed of ammonia crystals and ammonium hydrosulfate.

Cirriform

Bands of cloud resembling cirrus located mainly in the highest of three main layers that cover Jupiter.

Stratiform and Stratocumuliform

Wave and haze clouds that are seen mostly in the middle layer.

Cumuliform and cumulonimbiform

Convective clouds in the lowest layer that are capable of producing thunderstorms and may be composed at least partly of water droplets. an intermediate deck of ammonium hydrosulfide, and an inner deck of cumulus water clouds.

[Uranus] and [Neptune]

Clouds layers made mostly of methane gas.

Cirriform

High wispy formations resembling cirrus.

Stratiform

Layers of haze-cloud that lack any distinct features.

Cumuliform and cumulonimbiform

Lower-based convective clouds that can produce thunderstorms.