List of cloud types
Encyclopedia
Cloud
s are formed in Earth
's atmosphere when water
evaporates into vapor
from ocean
s, lake
s, 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.
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.
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 atlas
es.
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 color
s 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.
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
WMO varieties
Non-WMO variant
Abbreviation: Cc
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.
WMO species
WMO varieties
WMO supplementary features
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. 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
WMO varieties
WMO supplementary features -none
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
WMO varieties
WMO supplementary features
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
WMO varieties
WMO supplementary features
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
WMO varieties
WMO supplementary features
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
WMO varieties
WMO supplementary features - none
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
WMO varieties
WMO supplementary features
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
WMO varieties
WMO supplementary features
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
wind
s, and/or tornados at ground level.
WMO species
WMO Varieties -none
WMO supplementary features
Non-WMO informal term:
Nacreous
A thin usually cirriform-looking cloud seen most often between sunset
and sunrise
.
Contains supercooled nitric acid
and water droplets.
Subtypes
Consists of ice crystals only.
Columnar Clouds - rare, column-shaped.
Noctilucent
A thin mostly cirriform-looking cloud seen most often after sunset and before sunrise.
Very tenuous resembling cirrus.
Long streaks often in groups parallel or interwoven at small angles.
Subtypes
Clearly speaced roughly parallel short streaks.
Subtypes
Partial or rarely complete rings with dark centres.
Subtypes
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
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.
Cloud
A cloud is a visible mass of liquid droplets or frozen crystals made of water and/or various chemicals suspended in the atmosphere above the surface of a planetary body. They are also known as aerosols. Clouds in Earth's atmosphere are studied in the cloud physics branch of meteorology...
s are formed in Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
's atmosphere when water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
evaporates into vapor
Vapor
A vapor or vapour is a substance in the gas phase at a temperature lower than its critical point....
from ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
s, lake
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
s, and ponds or by evapotranspiration
Evapotranspiration
Evapotranspiration is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies...
over moist areas of Earth's land surface. The vapor rises up into colder areas of the atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
due to convective, orographic, or frontal lifting. The water vapor attaches itself to condensation
Condensation
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....
nuclei which could be anything from dust to microscopic particles of salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
and debris. Once the vapor has been cooled to saturation
Saturation
Saturation or saturated may refer to:- Meteorology :* Dew point, which is a temperature that occurs when atmospheric humidity reaches 100% and the air is saturated with moisture- Physics :...
, the cloud becomes visible. All weather producing clouds form in the troposphere
Troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....
, the lowest major layer of the atmosphere. However very small amounts of water vapor can be found higher up in the stratosphere
Stratosphere
The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...
and mesosphere
Mesosphere
The mesosphere is the layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere. In the mesosphere temperature decreases with increasing height. The upper boundary of the mesosphere is the mesopause, which can be the coldest naturally occurring...
and may condense into very thin clouds if the air temperatures are sufficiently cold. One branch of meteorology
Meteorology
Meteorology is the interdisciplinary scientific study of the atmosphere. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw breakthroughs occur after observing networks developed across several countries...
is focused on the study of nephology
Nephology
Nephology is the study of clouds and cloud formation. British meteorologist Luke Howard was a major researcher within this field, establishing a cloud classification system....
or cloud physics
Cloud physics
Cloud physics is the study of the physical processes that lead to the formation, growth and precipitation of clouds. Cloud formations are composed of microscopic droplets of liquid water , tiny crystals of ice , or both...
.
Tropospheric clouds can be divided into three main categories with names based on Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
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.
In the troposphere, nine of the ten genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
types are derived by cross-classifying the three categories into four families defined by altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
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
Cirrus cloud
Cirrus clouds are atmospheric clouds generally characterized by thin, wispy strands, giving them their name from the Latin word cirrus meaning a ringlet or curling lock of hair...
. High stratiform and cumuliform clouds carry the prefix cirro which yield the genera cirrostratus
Cirrostratus cloud
Cirrostratus clouds are thin, generally uniform clouds, composed of ice-crystals. They are difficult to detect and if capable of forming halos the cloud takes the form of thin cirrostratus nebulosus. The cloud has a fibrous texture with no haloes if it is thicker cirrostratus fibratus. On the...
and cirrocumulus
Cirrocumulus cloud
Cirrocumulus clouds are one of the three main types of high-altitude clouds, which also includes cirrus clouds and cirrostratus clouds. They usually occur at an altitude of to . Like other cumulus clouds, cirrocumulus clouds signify convection. Unlike other cirrus clouds, cirrocumulus include a...
. Middle cloud genera have the prefix alto (altostratus
Altostratus cloud
Altostratus is a cloud belonging to a class characterized by a generally uniform gray to bluish-gray sheet or layer, lighter in color than nimbostratus and darker than cirrostratus. The sun can be seen through thin altostratus, but thicker layers can be quite opaque...
and altocumulus
Altocumulus cloud
Altocumulus is a cloud belonging to a class characterized by globular masses or rolls in layers or patches, the individual elements being larger and darker than those of cirrocumulus and smaller than those of stratocumulus. Like other cumulus clouds, altocumulus signifies convection...
) to distinguish them from the high clouds, while low altitude stratiform and cumuliform genera (stratus
Stratus cloud
A stratus cloud is a cloud belonging to a class characterized by horizontal layering with a uniform base, as opposed to convective clouds that are as tall or taller than wide . More specifically, the term stratus is used to describe flat, hazy, featureless clouds of low altitude varying in color...
and stratocumulus
Stratocumulus cloud
A Stratocumulus cloud belongs to a class of clouds characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in altocumuli, and the whole being at a lower altitude, usually below 2,400 m...
) carry no height-related prefixes. The fourth family comprises stratiform and cumuliform genera of moderate vertical extent (nimbostratus
Nimbostratus cloud
A Nimbostratus cloud is characterized by a formless cloud layer that is almost uniformly dark gray. "Nimbo" is from the Latin word "nimbus", which denotes precipitation. It is generally a stratiform cloud of moderate vertical development that produces precipitation, developing cloud bases between...
and cumulus
Cumulus cloud
Cumulus clouds are a type of cloud with noticeable vertical development and clearly defined edges. Cumulus means "heap" or "pile" in Latin. They are often described as "puffy" or "cotton-like" in appearance. Cumulus clouds may appear alone, in lines, or in clusters...
) 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
Cumulonimbus cloud
Cumulonimbus is a towering vertical cloud that is very tall, dense, and involved in thunderstorms and other inclement weather. Cumulonimbus originates from Latin: Cumulus "Heap" and nimbus "rain". It is a result of atmospheric instability. These clouds can form alone, in clusters, or along a cold...
, 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.
The essentials of the modern nomenclature system for tropospheric clouds were proposed by Luke Howard
Luke Howard
Luke Howard FRS was a British manufacturing chemist and an amateur meteorologist with broad interests in science...
, a British
British people
The British are citizens of the United Kingdom, of the Isle of Man, any of the Channel Islands, or of any of the British overseas territories, and their descendants...
manufacturing chemist
Chemist
A chemist is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties such as density and acidity. Chemists carefully describe the properties they study in terms of quantities, with detail on the level of molecules and their component atoms...
and an amateur
Amateur
An amateur is generally considered a person attached to a particular pursuit, study, or science, without pay and often without formal training....
meteorologist with broad interests in science
Science
Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...
, in an 1802 presentation to the Askesian Society
Askesian Society
The Askesian Society was a debating club for scientific thinkers, established in 1796 in London. The name was taken from the Greek term Askesis, meaning 'training' or 'application'. It was founded by William Allen, who allowed the use of his laboratory at No...
. Since 1890, clouds are classified and illustrated in cloud atlas
Cloud atlas
A cloud atlas is a pictorial key to the nomenclature of clouds. Early cloud atlases were an important element in the training of meteorologists and in weather forecasting, and the author of a 1923 atlas stated that "increasing use of the air as a means of transportation will require and lead to a...
es.
Clouds that form above the troposphere have a generally cirriform structure, but are not given Latin names based on that characteristic. Polar
Polar
- Science, technology, and mathematics :*Polar , a satellite launched by NASA in 1996*Polar , a strongly magnetic cataclysmic variable star system...
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 color
Color
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...
s 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
Noctilucent cloud
Night clouds or Noctilucent clouds are tenuous cloud-like phenomena that are the "ragged-edge" of a much brighter and pervasive polar cloud layer called polar mesospheric clouds in the upper atmosphere, visible in a deep twilight. They are made of crystals of water ice. The name means roughly night...
which refers to their illumination during deep twilight
Twilight
Twilight is the time between dawn and sunrise or between sunset and dusk, during which sunlight scattering in the upper atmosphere illuminates the lower atmosphere, and the surface of the earth is neither completely lit nor completely dark. The sun itself is not directly visible because it is below...
. They are sub-classified alpha-numerically according to specific details of their cirriform physical structure.
Genus cirrus
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
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
, however, large amounts of cirrus clouds can indicate an approaching storm
Storm
A storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather...
system eventually followed by fair weather
Weather
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...
.
There are several variations of clouds of the cirrus genus based on species and varieties:
WMO species
- Cirrus fibratusCirrus fibratusCirrus fibratus is a type of cirrus cloud. The name cirrus fibratus is derived from Latin, meaning "fibrous". These clouds are similar to Cirrus uncinus, commonly known as "mares' tails"; however, fibratus clouds do not have tufts or hooks at the end. The filiments are usually separate from one...
- 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 uncinusCirrus uncinus cloudCirrus uncinus is a type of cirrus cloud. The name cirrus uncinus is derived from Latin, meaning "curly hooks". Also known as mares' tails, these clouds are generally sparse in the sky, and very thin....
- Cirrus uncinus
- Cirrus filaments with up-turned hooks or curls.
- Cirrus spissatusCirrus spissatus cloudCirrus spissatus clouds are the highest of the main cloud genera, and may sometimes even occur in the lower stratosphere. The characteristic features of cirrus clouds are fine threads or wisps of ice crystals, generally white, but appearing grey when dense and seen against the light. No...
- Cirrus spissatus
- Cirrus in the form of dense and opaque or mostly opaque patches.
- Cirrus castellanusCirrus castellanus cloudCirrus castellanus is a type of cirrus cloud. Its name comes from the word castellanus, which means "of a fort, of a castle" in Latin. Like all cirrus clouds, the clouds occur at high altitudes. They appear as separate turrets rising from a lower-level cloud base. Often these cloud turrets form in...
- Cirrus castellanus
- A series of dense lumps, or "towers" of cirrus, connected by a thinner base.
- Cirrus floccusCirrus floccusCirrus floccus is a type of cirrus cloud. The name cirrus floccus is derived from Latin, meaning "a lock of wool". Cirrus floccus occurs as small tufts of cloud, usually with a ragged base. The cloud can have virga falling from it, but the precipitation does not reach the ground. The individual...
- Cirrus floccus
- Cirrus with elements which take on a rounded appearance on the top, with the lower part appearing ragged.
- Cirrus vertebratusCirrus vertebratusCirrus vertebratus is a type of cirrus cloud. The name cirrus vertebratus is derived from Latin, meaning "jointed, articulated, vertebrated". Like cirrus intortus, the vertebratus species is exclusive to the cirrus genus...
- Cirrus vertebratus
- Cirrus with elements arranged in the manner of a vertebrae or fishFishFish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
skeletonSkeletonThe skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...
.
WMO varieties
- Cirrus undulatus
- Undulating cirrus.
- Cirrus duplicatusCirrus duplicatusCirrus duplicatus is a variety of cirrus cloud. The name cirrus duplicatus is derived from Latin, meaning "double". The duplicatus variety of cirrus clouds occurs when there are at least two layers of cirrus clouds. Most of the time, occurrences of cirrus fibratus and cirrus uncinus are in the...
- Cirrus duplicatus
- Sheets of cirrus at different layers of the atmosphere, which may be connected at one or more points.
- Cirrus intortusCirrus intortus cloudCirrus intortus is a variety of cirrus cloud. The name cirrus intortus is derived from Latin, meaning "twisted, wound". The variety of intortus clouds is specific to cirrus clouds, and they appear as interwound strands of cirrus clouds with a purely random pattern...
- Cirrus intortus
- Cirrus clouds whose filaments are irregularly curved or tangled.
- Cirrus radiatusCirrus radiatusCirrus radiatus is a variety of cirrus cloud. The name cirrus radiatus is derived from Latin, meaning "rayed, striped". This variety of cirrus clouds occurs in parallel bands that often cover the entire sky and appear to converge at a single point or two opposite points on the horizon. Cirrus...
- Cirrus radiatus
- Large area of cirrus displaying horizontal bands that appear to converge at the horizonHorizonThe horizon is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting...
.
Non-WMO variant
- Cirrus aviaticusContrailContrails or vapour trails are artificial clouds that are the visible trails of condensed water vapour made by the exhaust of aircraft engines...
- Persistent condensation trails (contrails) formed by ice crystals originating from water vapor emitted by aircraft engineEngineAn engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...
s.
Genus cirrocumulus
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.
WMO species
- Cirrocumulus castellanusCirrocumulus castellanusCirrocumulus castellanus is a type of cirrocumulus cloud. The name cirrocumulus catellanus is derived from Latin, meaning "of a castle". These clouds appear as round turrets that are rising from either a lowere line or sheet of clouds. Cirrocumulus castellanus is an indicator of atmospheric...
- Cirrocumulus with "towers", or turretTurretIn architecture, a turret is a small tower that projects vertically from the wall of a building such as a medieval castle. Turrets were used to provide a projecting defensive position allowing covering fire to the adjacent wall in the days of military fortification...
s.- Cirrocumulus floccusCirrocumulus floccusCirrocumulus floccus is a type of cirrocumulus cloud. The name cirrocumulus floccus is derived from Latin, meaning "a lock of wool". Cirrocumulus floccus appears as small tufts of cloud with rounded heads, but ragged bottoms. The cloud can produce virga, precipitation that evaporates before...
- Cirrocumulus floccus
- Cirrocumulus in the form of tufts with ragged bases.
- Cirrocumulus lenticularisCirrocumulus lenticularisCirrocumulus lenticularis is a type of cirrocumulus cloud. The name cirrocumulus lenticularis is derived from Latin, meaning "like a lentil". Cirrocumulus lenticularis are smooth clouds that have the appearance of a lens or an almond. They usually form at the crests of atmospheric waves, which...
- Cirrocumulus lenticularis
- Lenticular, or lensLens-Optics:*Lens , an optical element which converges or diverges light**Lens , a part of the eye**Corrective lens for correction of human vision***Contact lens, placed on the cornea of the eye**Photographic lens, a lens designed for use on a camera...
-shaped cirrocumulus.- Cirrocumulus stratiformisCirrocumulus stratiformisCirrocumulus stratiformis is a type of cirrocumulus cloud. The name cirrocumulus stratiformis is derived from Latin, meaning "stretched out". Cirrocumulus stratiformus occurs as very small cirrocumulus clouds that cover a large part of the sky. This type of cloud always occurs in thin layers...
- Cirrocumulus stratiformis
- Sheets or relatively flat patches of cirrocumulus.
WMO varieties
- Cirrocumulus undulatusCirrocumulus undulatusCirrocumulus undulatus is a variety of cirrocumulus cloud. The name cirrocumulus undulatus is derived from Latin, meaning "1.diversified as with waves". They have a rippled appearance due to wind shear and usually cover only a small portion of the sky. They appear in bands as small patches or...
- undulating cirrocumulus.
- Cirrocumulus lacunosusCirrocumulus lacunosusCirrocumulus lacanosus is a type of cirrocumulus cloud. The name cirrocumulus lacanosus is derived from Latin, meaning "full of hollows". Cirrocumulus lacanosus is a relatively rare cloud form that occurs as a layer of cloud with circular holes in it...
- Cirrocumulus lacunosus
- Cirrocumulus with large clear holes.
WMO supplementary features
- Cirrocumulus mamma
- Cirrocumulus with bubble-like downward protuberances.
- Cirrocumulus virga
- Cirrocumulus producing light precipitationPrecipitationPrecipitation may refer to:* Precipitation , rain, sleet, hail, snow and other forms of water falling from the sky* Precipitation , the condensation of a solid from a solution during a chemical reaction...
that evaporates well above ground level.
Genus cirrostratus
Abbreviation: CsClouds 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. Frontal cirrostratus is a precursor to rain or snow
Snow
Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...
if it thickens into mid level altostratus and eventually nimbostratus as the weather front
Weather front
A weather front is a boundary separating two masses of air of different densities, and is the principal cause of meteorological phenomena. In surface weather analyses, fronts are depicted using various colored lines and symbols, depending on the type of front...
moves closer to the observer.
WMO species
- Cirrostratus fibratusCirrostratus fibratusCirrostratus fibratus is a type of cirrostratus cloud. The name cirrostratus fibratus is derived from Latin, meaning "fibrous". Cirrostratus fibratus is one of the two most common forms that cirrostratus often takes, with the other being cirrostratus nebulosus. They are formed from strong,...
- Cirrostratus sheet with a fibrous appearance, but not as detached as cirrus.
- Cirrostratus nebulosusCirrostratus nebulosusCirrostratus nebulosus is a type of cirrostratus cloud. The name cirrostratus nebulosus is derived from Latin, meaning "full of vapor, foggy, cloudy, dark"...
- Cirrostratus nebulosus
- Featureless, uniform cirrostratus.
WMO varieties
- Cirrostratus duplicatus
- separate or semi-merged sheets of cirrostratus with one layer slightly above the other.
- Cirrostratus undulatus
- Cirrostratus in undulating waveWaveIn physics, a wave is a disturbance that travels through space and time, accompanied by the transfer of energy.Waves travel and the wave motion transfers energy from one point to another, often with no permanent displacement of the particles of the medium—that is, with little or no associated mass...
s.
WMO supplementary features -none
Genus altocumulus
Abbreviation: AcClouds of the genus altocumulus are not always associated with a weather front but can still bring precipitation, usually in the form of virga
Virga
In meteorology, virga is an observable streak or shaft of precipitation that falls from a cloud but evaporates before reaching the ground. At high altitudes the precipitation falls mainly as ice crystals before melting and finally evaporating; this is usually due to compressional heating, because...
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 variant altocumulus Kelvin-Helmholtz cloud, lenticular spiral indicative of severe turbulenceTurbulenceIn fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
.- 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 sunSunThe Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
or moonMoonThe Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
.- 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
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.
Genus stratocumulus
Abbreviation: ScClouds 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
Clouds of the genus stratus
Stratus
-Weather:*Stratus cloud, a cloud type**Nimbostratus cloud, a cloud type**Stratocumulus cloud, a cloud type**Altostratus cloud, a cloud type**Altostratus undulatus cloud, a cloud type**Cirrostratus cloud, a cloud type-Music:...
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
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 virgaNimbostratus virgaNimbostratus virga is a form of Nimbostratus cloud in which the precipitation never reaches the ground. It retains the same features as a normal nimbostratus cloud; dark in appearance, low to medium level cloud of moderate vertical development and made up of sheets....
- Nimbostratus virga
- Nimbostratus producing precipitation that evaporates before reaching the ground.
Genus cumulus
Abbreviation: CuCumulus
Cumulus is a type of cloud with the appearance of a lump of cotton wool.Cumulus may also refer to:*Cumulus Media, a radio broadcasting company*Cumulus , digital asset management software developed by Canto Software*Reinhard Cumulus, glider...
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
Cumulonimbus cloud
Cumulonimbus is a towering vertical cloud that is very tall, dense, and involved in thunderstorms and other inclement weather. Cumulonimbus originates from Latin: Cumulus "Heap" and nimbus "rain". It is a result of atmospheric instability. These clouds can form alone, in clusters, or along a cold...
. 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.
- Cumulus humilisCumulus humilis cloudCumulus humilis is a low to middle cloud with small vertical extent that is commonly referred to as "fair weather cumulus". In hot countries and over mountainous terrain these clouds occur at up to 6000 meters altitude, though elsewhere they are typically found lower.They are formed by rising warm...
- Cumulus humilis
- "Fair weather clouds" with flat light grey bases and small white domed tops.
- Cumulus mediocrisCumulus mediocris cloudCumulus mediocris is a low to middle level cloud with some vertical extent of the genus cumulus, larger in vertical development than Cumulus humilis. It may or may not show the cauliflower form characteristic of cumulus clouds...
- Cumulus mediocris
- Cumulus clouds with flat medium grey bases and higher tops than cumulus humilis.
- Cumulus congestus
- Large cumulus clouds with flat dark grey bases and very tall tower-like formations. Also known informally as towering cumulus (TCU), especially in aviationAviationAviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Aviation is derived from avis, the Latin word for bird.-History:...
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
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
Airmass
In astronomy, air mass is the optical path length through Earth’s atmosphere for light from a celestial source. As it passes through the atmosphere, light is attenuated by scattering and absorption; the more atmosphere through which it passes, the greater the attenuation. Consequently, celestial...
is convectively highly unstable. They generally produce thunderstorms, rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
or showers, and sometimes hail
Hail
Hail is a form of solid precipitation. It consists of balls or irregular lumps of ice, each of which is referred to as a hail stone. Hail stones on Earth consist mostly of water ice and measure between and in diameter, with the larger stones coming from severe thunderstorms...
, strong outflow
Outflow
Outflow may refer to:*Capital outflow - an economic term describing capital flowing out of a particular economy.*Bipolar outflow in astronomy represents two continuous flows of gas from the poles of a star....
wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
s, and/or tornados at ground level.
WMO species
- Cumulonimbus calvusCumulonimbus calvusCumulonimbus calvus is a moderately tall cumulonimbus cloud which is capable of precipitation, but has not yet reached the height where it forms into a cumulonimbus capillatus or cumulonimbus incus...
- Cumulonimbus with high domed top.
- Cumulonimbus capillatus
- Cumulonimbus with high cirriform top.
WMO Varieties -none
WMO supplementary features
- Cumulonimbus incusCumulonimbus incusA cumulonimbus incus is a cumulonimbus cloud which has reached the level of stratospheric stability and has formed the characteristic flat, anvil-top shape...
- 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:
- Hot towerHot towerA hot tower is a tropical cumulonimbus cloud that penetrates the tropopause, i.e. it reaches out of the lowest layer of the atmosphere, the troposphere, into the stratosphere. In the tropics, the tropopause typically lies at least 15 km above sea level...
- A tropical cumulonimbus cloud that penetrates the tropopauseTropopauseThe tropopause is the atmospheric boundary between the troposphere and the stratosphere.-Definition:Going upward from the surface, it is the point where air ceases to cool with height, and becomes almost completely dry...
.
NacreousPolar stratospheric cloudPolar stratospheric clouds or PSCs, also known as nacreous clouds , are clouds in the winter polar stratosphere at altitudes of 15,000–25,000 meters...
(mother of pearl)
A thin usually cirriform-looking cloud seen most often between sunsetSunset
Sunset or sundown is the daily disappearance of the Sun below the horizon in the west as a result of Earth's rotation.The time of sunset is defined in astronomy as the moment the trailing edge of the Sun's disk disappears below the horizon in the west...
and sunrise
Sunrise
Sunrise is the instant at which the upper edge of the Sun appears above the horizon in the east. Sunrise should not be confused with dawn, which is the point at which the sky begins to lighten, some time before the sun itself appears, ending twilight...
.
- Type 1
Contains supercooled nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
and water droplets.
Subtypes
- Crystals of nitric acid and water.
- Additionally contains supercooled sulfuric acidSulfuric acidSulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
in ternary solution.
- Type 2
Consists of ice crystals only.
Columnar Clouds - rare, column-shaped.
NoctilucentNoctilucent cloudNight clouds or Noctilucent clouds are tenuous cloud-like phenomena that are the "ragged-edge" of a much brighter and pervasive polar cloud layer called polar mesospheric clouds in the upper atmosphere, visible in a deep twilight. They are made of crystals of water ice. The name means roughly night...
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
- Streaks with diffuse, blurred edges.
- Streaks with sharply defined edges.
- Type 3: Billows
Clearly speaced roughly parallel short streaks.
Subtypes
- Short, straight narrow streaks.
- Wave-like structure with undulations.
- Type 4: Whirls
Partial or rarely complete rings with dark centres.
Subtypes
- Whirls of small angular radius of curvature, sometimes resembling light ripples on a water surface.
- Simple curve of medium angular radius with one or more bands.
- Whirls with large scale ring structure.
VenusVenusVenus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
Thick overcast mostly stratiform clouds of sulfur dioxideSulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
that obscure the planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
's surface.
MarsMarsMars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
High thin scattered mostly cirriform clouds of waterWater
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...
through which the planet's surface can be seen. Morning fog of water and/or carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
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.
JupiterJupiterJupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
and SaturnSaturnSaturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
Overcast mostly stratiform cloud decks in parallel latitudinal bands at the tropopauseTropopause
The tropopause is the atmospheric boundary between the troposphere and the stratosphere.-Definition:Going upward from the surface, it is the point where air ceases to cool with height, and becomes almost completely dry...
alternatingly composed of ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
crystals and ammonium
Ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
hydrosulfate. Lower layer with some cumuliform water cloud can create thunderstorms.
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
- AltocumulusAltocumulus cloudAltocumulus is a cloud belonging to a class characterized by globular masses or rolls in layers or patches, the individual elements being larger and darker than those of cirrocumulus and smaller than those of stratocumulus. Like other cumulus clouds, altocumulus signifies convection...
– altus and cumulus – high (middle) heap. - AltostratusAltostratus cloudAltostratus is a cloud belonging to a class characterized by a generally uniform gray to bluish-gray sheet or layer, lighter in color than nimbostratus and darker than cirrostratus. The sun can be seen through thin altostratus, but thicker layers can be quite opaque...
– altus and stratus – high (middle) flat layer. - CirrocumulusCirrocumulus cloudCirrocumulus clouds are one of the three main types of high-altitude clouds, which also includes cirrus clouds and cirrostratus clouds. They usually occur at an altitude of to . Like other cumulus clouds, cirrocumulus clouds signify convection. Unlike other cirrus clouds, cirrocumulus include a...
– cirrus and cumulus – thin, wispy and puffy. - CirrostratusCirrostratus cloudCirrostratus clouds are thin, generally uniform clouds, composed of ice-crystals. They are difficult to detect and if capable of forming halos the cloud takes the form of thin cirrostratus nebulosus. The cloud has a fibrous texture with no haloes if it is thicker cirrostratus fibratus. On the...
– cirrus and stratus – thin, wispy and spread into flat layer. - CirrusCirrus cloudCirrus clouds are atmospheric clouds generally characterized by thin, wispy strands, giving them their name from the Latin word cirrus meaning a ringlet or curling lock of hair...
– thin and wispy. - CumulonimbusCumulonimbus cloudCumulonimbus is a towering vertical cloud that is very tall, dense, and involved in thunderstorms and other inclement weather. Cumulonimbus originates from Latin: Cumulus "Heap" and nimbus "rain". It is a result of atmospheric instability. These clouds can form alone, in clusters, or along a cold...
– cumulus and nimbus – rain-bearing heap. The cumulonimbus cloud can cause thunderstorms and tornados. - CumulusCumulus cloudCumulus clouds are a type of cloud with noticeable vertical development and clearly defined edges. Cumulus means "heap" or "pile" in Latin. They are often described as "puffy" or "cotton-like" in appearance. Cumulus clouds may appear alone, in lines, or in clusters...
– puffy. - NimbostratusNimbostratus cloudA Nimbostratus cloud is characterized by a formless cloud layer that is almost uniformly dark gray. "Nimbo" is from the Latin word "nimbus", which denotes precipitation. It is generally a stratiform cloud of moderate vertical development that produces precipitation, developing cloud bases between...
- nimbus and stratus - rain-bearing layer. - StratocumulusStratocumulus cloudA Stratocumulus cloud belongs to a class of clouds characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in altocumuli, and the whole being at a lower altitude, usually below 2,400 m...
, (Cumulostratus) - stratus and cumulus - heap spread into flat layer. - StratusStratus cloudA stratus cloud is a cloud belonging to a class characterized by horizontal layering with a uniform base, as opposed to convective clouds that are as tall or taller than wide . More specifically, the term stratus is used to describe flat, hazy, featureless clouds of low altitude varying in color...
- flat layer.
Alphabetical list WMO tropospheric species
- Castellanus – castle-like with a series of turretTurretIn architecture, a turret is a small tower that projects vertically from the wall of a building such as a medieval castle. Turrets were used to provide a projecting defensive position allowing covering fire to the adjacent wall in the days of military fortification...
shapes – indicates air mass instability. - Congestus – great verticsal development and heaped into cauliflowerCauliflowerCauliflower is one of several vegetables in the species Brassica oleracea, in the family Brassicaceae. It is an annual plant that reproduces by seed...
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 woolWoolWool is the textile fiber obtained from sheep and certain other animals, including cashmere from goats, mohair from goats, qiviut from muskoxen, vicuña, alpaca, camel from animals in the camel family, and angora from rabbits....
- indicates some mid and/or high level instability. - FractusFractus cloudFractus clouds are small, ragged cloud fragments that are usually found under an ambient cloud base. They form or have broken off from a larger cloud, and are generally sheared by strong winds, giving them a jagged, shredded appearance. Fractus have irregular patterns, appearing much like torn...
– irregular shredded appearance – forms in precipitation and/or gusty winds. - Humilis – small, low, flattened cumulus – indicates relatively slight airmass instability.
- Lenticular cloudLenticular cloudLenticular clouds are stationary lens-shaped clouds that form at high altitudes, normally aligned perpendicular to the wind direction. Lenticular clouds can be separated into altocumulus standing lenticularis , stratocumulus standing lenticular , and cirrocumulus standing lenticular...
– having a lens-like appearance – formed by standing waveWaveIn physics, a wave is a disturbance that travels through space and time, accompanied by the transfer of energy.Waves travel and the wave motion transfers energy from one point to another, often with no permanent displacement of the particles of the medium—that is, with little or no associated mass...
s of wind passing over mountainMountainImage:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...
s 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
WMO terms
- ArcusArcus cloudAn arcus cloud is a low, horizontal cloud formation. Roll clouds and shelf clouds are the two types of arcus clouds. A shelf cloud is usually associated with the leading edge of thunderstorm outflow; roll clouds are usually formed by outflows of cold air from sea breezes or cold fronts in the...
– 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 (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.
- PileusPileus (meteorology)A pileus , also called scarf cloud or cap cloud, is a small, horizontal cloud that can appear above a cumulus or cumulonimbus cloud, giving the parent cloud a characteristic "hoodlike" appearance. Pilei tend to change shape rapidly. They are formed by strong updrafts acting upon moist air at lower...
– 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 boneBoneBones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
s, a skeletonSkeletonThe skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...
or calciumCalciumCalcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
.
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 cloudAccessory cloudAn accessory cloud is a cloud which is dependent on a larger cloud system for its development and continuance. It is often an appendage but also can be adjacent to the parent cloud system...
(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 topOvershooting topAn overshooting top is a dome-like protrusion that shoots out of the top of the anvil of a thunderstorm. When an overshooting top is present for 10 minutes or longer, it is a strong indication that the thunderstorm may be severe....
on a Cb that is often present on a supercellSupercellA supercell is a thunderstorm that is characterized by the presence of a mesocyclone: a deep, continuously-rotating updraft. For this reason, these storms are sometimes referred to as rotating thunderstorms...
. - Anvil rollover – (slang) circular protrusion attached to underside of anvil.
- Arcus cloudArcus cloudAn arcus cloud is a low, horizontal cloud formation. Roll clouds and shelf clouds are the two types of arcus clouds. A shelf cloud is usually associated with the leading edge of thunderstorm outflow; roll clouds are usually formed by outflows of cold air from sea breezes or cold fronts in the...
(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 downdraftRear flank downdraftThe rear flank downdraft or RFD is a region of dry air wrapping around the back of a mesocyclone in a supercell thunderstorm. These areas of descending air are thought to be essential in the production of many supercellular tornadoes...
descends and dries out cloud and occludes around a mesocycloneMesocycloneA mesocyclone is a vortex of air, approximately 2 to 10 miles in diameter , within a convective storm....
. - 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 cloudFunnel cloudA funnel cloud is a funnel-shaped cloud of condensed water droplets, associated with a rotating column of wind and extending from the base of a cloud but not reaching the ground or a water surface. A funnel cloud is usually visible as a cone-shaped or needle like protuberance from the main cloud...
aloft or a tornado. - Altocumulus castellanus (WMO genus and species) - castle crenellation-shaped altocumulus clouds.
- CumulusCumulus cloudCumulus clouds are a type of cloud with noticeable vertical development and clearly defined edges. Cumulus means "heap" or "pile" in Latin. They are often described as "puffy" or "cotton-like" in appearance. Cumulus clouds may appear alone, in lines, or in clusters...
(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 fractusFractus cloudFractus clouds are small, ragged cloud fragments that are usually found under an ambient cloud base. They form or have broken off from a larger cloud, and are generally sheared by strong winds, giving them a jagged, shredded appearance. Fractus have irregular patterns, appearing much like torn...
(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 calvusCumulonimbus calvusCumulonimbus calvus is a moderately tall cumulonimbus cloud which is capable of precipitation, but has not yet reached the height where it forms into a cumulonimbus capillatus or cumulonimbus incus...
(WMO genus and species) – cumulonimbus with round tops like cumulus congestus. - Cumulonimbus capillatus (WMO genus and species) - Cb with cirriform top.
- Cumulonimbus incusCumulonimbus incusA cumulonimbus incus is a cumulonimbus cloud which has reached the level of stratospheric stability and has formed the characteristic flat, anvil-top shape...
(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 tornadoTornadoA tornado is a violent, dangerous, rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. They are often referred to as a twister or a cyclone, although the word cyclone is used in meteorology in a wider...
. - Hail fog (informal term) - a shallow surface layer of fogFogFog is a collection of water droplets or ice crystals suspended in the air at or near the Earth's surface. While fog is a type of stratus cloud, the term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated...
that sometimes forms in vicinity of deep hailHailHail is a form of solid precipitation. It consists of balls or irregular lumps of ice, each of which is referred to as a hail stone. Hail stones on Earth consist mostly of water ice and measure between and in diameter, with the larger stones coming from severe thunderstorms...
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 cloudFunnel cloudA funnel cloud is a funnel-shaped cloud of condensed water droplets, associated with a rotating column of wind and extending from the base of a cloud but not reaching the ground or a water surface. A funnel cloud is usually visible as a cone-shaped or needle like protuberance from the main 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 (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 cloudWall cloudA wall cloud is a large, lowering, and rotating base of a cumulonimbus cloud that potentially forms tornadoes. It is typically beneath the rain-free base portion of a deep cumulus cloud , and indicates the area of primary and strongest updraft which condenses into cloud at altitudes lower than...
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 cloudWall cloudA wall cloud is a large, lowering, and rotating base of a cumulonimbus cloud that potentially forms tornadoes. It is typically beneath the rain-free base portion of a deep cumulus cloud , and indicates the area of primary and strongest updraft which condenses into cloud at altitudes lower than...
(informal term) – distinctive fairly large lowering of the rain free base of a Cb, often rotating.