Weird looking Clouds Explained


There are clouds of many types, forms and shapes, often given the wildest explanations. So let’s go through some photos of some of the strangest, most beautiful cloud types along with the information to help us understand what they are or how they form.

About Clouds

In meteorology, a cloud is a visible mass of liquid droplets or frozen crystals made of water or various chemicals suspended in the atmosphere above the surface of a planetary body. These suspended particles are also known as aerosols. Clouds in earth’s atmosphere are studied in the cloud physics branch of meteorology. Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapor to the air. In general, precipitation will fall to the surface; an exception is virga, which evaporates before reaching the surface.

Clouds can show convective development like cumulus, appear in layered sheets such as stratus, or take the form of thin fibrous wisps, as in the case of cirrus. Prefixes are used in connection with clouds: strato- for low cumuliform-category clouds that show some stratiform characteristics, nimbo– for thick stratiform clouds that can produce moderate to heavy precipitation, alto– for middle clouds, and cirro– for high clouds. Whether or not a cloud is low, middle, or high level depends on how far above the ground its base forms.
Read more about clouds >> 

 


Lenticular clouds (Altocumulus lenticularis) 

Lenticular clouds

Lenticular clouds (Altocumulus lenticularis) or Lens 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 (ACSL), stratocumulus standing lenticular (SCSL), and cirrocumulus standing lenticular (CCSL).
Due to their shape, they have been offered as an explanation for some Unidentified Flying Object (UFO) sightings.

More info: Lenticular clouds (Altocumulus lenticularis) 

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 Pileus Clouds 

Pileus (meteorology)

A pileus (/ˈpləs/; Latin for cap), also called scarf cloud or cap cloud, is a small, horizontal, lenticular 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 updraft at lower altitudes, acting upon moist air above, causing the air to cool to its dew point. As such, they are usually indicators of severe weather, and a pileus found atop a cumulus cloud often foreshadows transformation into a cumulonimbus cloud, as it indicates a strong updraft within the cloud.

Clouds that are attached to pilei are often given the suffix “pileus” or “with pileus”. For example, a cumulonimbus cloud with a pileus attached to it would be called “cumulonimbus with pileus”.

volcano cloudPilei can also form above ash clouds and pyrocumulus clouds from erupting volcanoes (see the image to the left).

Pilei form above some mushroom clouds of high-yield nuclear detonations.

A sheet of altostratus cloud often is seen lower down in a cumulonimbus cloud, this is known as a velum cloud.

 

Lenticular clouds5

Lenticular clouds4

Pileus

Pileus

Pileus Iridescent Cloud

Lenticular clouds3
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Undulatus asperatus 

Asperatus Cloud, New Zealand

Asperatus Cloud, New Zealand

Undulatus asperatus: This apparently new class of clouds, is still a mystery. But experts suspect asperatus clouds’ choppy undersides may be due to strong winds disturbing previously stable layers of warm and cold air.
Asperatus clouds may spur the first new classification in the World Meteorological Organization’s International Cloud Atlas since the 1950s, Gavin Pretor-Pinney said.
Since the last addition to the atlas, the emergence of satellite imagery has pushed meteorologists to take a much broader view on weather and focus less on small-scale cloud formations.

More info: Undulatus asperatus

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Asperatus - Undulatus asperatus2 29939_404024898432_4828430_n Asperatus - Undulatus asperatus

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Mammatus cloud 

Mammatus cloud

Mammatus, also known as mammatocumulus (meaning “mammary cloud” or “breast cloud”), is a meteorological term applied to a cellular pattern of pouches hanging underneath the base of a cloud. The name mammatus, derived from the Latin mamma (meaning “udder” or “breast”), refers to a resemblance between the characteristic shape of these clouds and the breast of a woman.

More info: Mammatus | Source

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Gallery
Mammatus clouds
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Kelvin–Helmholtz waves 

Wave cloudThese crazy clouds that look like a row of crashing waves are known as Kelvin–Helmholtz instability . They form when two layers of air or liquid of different densities move past each other at different speeds, creating shearing at the boundary.

It could be like oil and vinegar. In the ocean, the top is warm and the bottom is really cold. It’s like a thin layer of oil on a big puddle of water.
When these two layers move past each other, a Kelvin-Helmholz instability is formed that is sort of like a wave. Parts of the boundary move up and parts move down. Because one layer is moving faster than the other, the shear causes the tops of the waves to move horizontally, forming what looks like an ocean wave crashing on the beach.
It really is like breaking waves. A wave breaks when the water on top moves so much faster than the water below that it kind of piles up on itself. Source

The Kelvin–Helmholtz instability (after Lord Kelvin and Hermann von Helmholtz) can occur when there is velocity shear in a single continuous fluid, or where there is a velocity difference across the interface between two fluids. An example is wind blowing over water: The instability manifests in waves on the water surface. More generally, clouds, the ocean, Saturn’s bands, Jupiter’s Red Spot, and the sun’s corona show this instability

More info: Kelvin–Helmholtz instability

Wave cloud2

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A fallstreak hole or punch hole cloud 

 

Fallstreak hole phenomenon or hole punch cloud over Novokosino, Moscow, Russia

Fallstreak hole phenomenon or hole punch cloud over Novokosino, Moscow, Russia.

A fallstreak hole, also known as a hole punch cloud, punch hole cloud, skypunch, canal cloud, sky canal or cloud hole, is a large circular gap that can appear in cirrocumulus or altocumulus clouds. Such holes are formed when the water temperature in the clouds is below freezing but the water has not frozen yet due to the lack of ice nucleation particles (see supercooled water). When a portion of the water does start to freeze it will set off a domino effect, due to the Bergeron process, causing the water vapor around it to freeze and fall to the earth as well. This leaves a large, often circular, hole in the cloud.

It is believed that a disruption in the stability of the cloud layer, such as that caused by a passing jet, may induce the domino process of evaporation which creates the hole. Such clouds are not unique to any one geographic area and have been photographed from many places.
Because of their rarity and unusual appearance, as well as very little exposure in media, fallstreak holes are often mistaken for or attributed to unidentified flying objects (UFO).


fallstreak hole - punch cloud

 

A fallstreak hole - punch cloud.

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Sky Canals 

Sky Canals

Using Landsat 5 data from the USGS Global Visualization Viewer.If residents of rural West Virginia were to have looked up into the sky Dec. 11, 2009, they would have seen a halo of light bursting through the thin bank of clouds that hung overhead. The light was streaming through hole-punch clouds and canals, most likely created by passing airplanes. The strange cloud phenomenon was captured that day by NASA’s Landsat-5 satellite.
Credit: Rob Simmon | source

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Arcus cloud or Roll cloud 

Arcus cloud or Roll cloud

An arcus cloud roll cloud or morning glory 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 absence of thunderstorms.

More info: arcus cloud 

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Morning glory clouds

Odd, rare clouds also known as Morning Glory clouds without providing an explanation for how they form.
Meteorologist Roger Smith of the University of Munich, has studied their formation.
“Over the years we’ve developed a good understanding of them,” Smith said. “It’s no longer a mystery, but still very spectacular.”
The Morning Glory phenomenon is the result of the particular configuration of the land and sea on the Cape York Peninsula, in a remote part of Australia. The peninsula tapers off from about 350 miles wide to 60 miles as it extends north between the Gulf of Carpentaria to the west and the Coral Sea to the east. The easterly trade winds push the sea breeze across the peninsula during the daytime, which meets the sea breeze from the west coast in the late evening. The collision produces a wave disturbance moving inland to the southwest that is a key part of the cloud formation.
As moist sea air is lifted to the crest of the waves, it cools and condensation forms a cloud. Sometimes there is just one wave, but Smith has seen as many as 10 together in a series.
“If you look at the clouds, it looks as if they are rolling backwards,” Smith said. “But in fact the clouds are continuously formed at the leading edge and continuously eroded at the trailing edge. That gives a rolling appearance.”
These clouds do occur elsewhere, including Munich, where they form about once in a decade. Cape York is unique because they happen regularly in the fall above the small town of Burketown. And they can also be particularly impressive there as well, growing up to 600 miles long. Pilots fly into the area every year, hoping to see the intriguing clouds.
Not many scientists study them, or really any weird clouds, because their very rarity makes them relatively unimportant for studying precipitation or climate. So, oftentimes, their formation is poorly understood.
“It’s hard to get funding to study something that’s neat looking,” said cloud physicist Patrick Chuang of the University of California, Santa Cruz.

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Circumhorizontal Arc 

Circumhorizontal Arc over Europe

Circumhorizontal Arc over Europe

A circumhorizontal arc is an optical phenomenon – an ice-halo formed by plate-shaped ice crystals in high level cirrus clouds.

Other currently accepted names for the phenomenon are circumhorizon arc or lower symmetric 46° plate arc.The misleading term “fire rainbow” is sometimes used to describe these phenomena, although they are neither rainbows, nor related in any way to fire.
The complete halo is a huge, multi-coloured band running parallel to the horizon with its centre beneath the sun. The distance below the sun is twice as far as the common 22-degree halo. Red is the uppermost colour. Often, when the halo-forming cloud is small or patchy, only fragments of the arc are seen.
A circumhorizontal arc may be difficult to distinguish from an infralateral arc when the sun is high in the sky. The former is always parallel to the horizon, whereas the latter curves upward at its ends.

More info: circumhorizontal arc | cirrus clouds 

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Cloud iridescence

This timelapse of these interesting clouds were filmed over Santa Clarita, California in February of 2012. They were forming along with a large lenticular-like cirrus wave structure, about an hour or so before sunset, and provided some very colorful displays.

Cloud iridescence is the occurrence of colors in a cloud similar to those seen in oil films on puddles, and is similar toirisation. It is a fairly uncommon phenomenon, most often observed in altocumuluscirrocumulus, lenticular clouds and cirrus clouds.The colors are usually pastel, but can be very vivid. Iridescence is generally produced near the sun, with the sun’s glare masking it, so it is more easily seen by hiding the sun behind a tree or building. Other aids are dark glasses, or observing the sky reflected in a convex mirror or in a pool of water.

Iridescent clouds are a diffraction phenomenon caused by small water droplets or small ice crystals individually scattering light. Larger ice crystals produce halos.

If parts of clouds have small droplets or crystals of similar size, their cumulative effect is seen as colors. The cloud must be optically thin, so that most rays encounter only a single droplet. Iridescence is therefore mostly seen at cloud edges or in semi-transparent clouds, and newly forming clouds produce the brightest and most colorful iridescence. When a thin cloud has droplets of similar size over a large extent, the iridescence takes on the structured form of acorona, a central bright disk around the sun or moon surrounded by one or more colored rings. In one instance a lunar corona was observed, with the iridescent cirrus cloud 11–13.6 km (36,000–45,000 ft) above the mean sea level at a temperature of −70 °C (−94 °F). The pure corona was 9.5 km (31,000 ft) above the mean sea level, at a temperature of −60 °C (−76 °F)

Iredescence clouds often have been mistaken for earthquake clouds which are a completely different phenomenon. Earthquake clouds are clouds claimed to be signs of imminent earthquakes.

 

Pileus

Pileus Iridescent Cloud

 


Polar stratospheric clouds 

Polar stratospheric clouds or PSCs, also known as nacreous clouds

Polar stratospheric clouds or PSCs, also known as nacreous clouds, from nacre, or mother of pearl, due to its iridescence), are clouds in the winter polar stratosphere at altitudes of 15,000–25,000 meters (49,000–82,000 ft). They are implicated in the formation of ozone holes; their effects on ozone depletion arise because they support chemical reactions that produce active chlorine which catalyzes ozone destruction, and also because they remove gaseous nitric acid, perturbing nitrogen and chlorine cycles in a way which increases ozone destruction.
These clouds, also known as “mother of pearl clouds,” form in the stratosphere far above the usual realm of weather. They are seldom seen, but when they are, the reports usually come from high-northern parts of our planet.
Atmospheric optics expert Les Cowley explains the special conditions required to create such a cloud: “Take an unusually cold lower stratosphere (15-25km high), use some gravity waves generated by high winds and storms in the troposphere  to stir in some water vapour, and — voilà! You get these clouds made of tiny ice crystals shining after sunset with unforgettably bright iridescent colors.”
“The very special conditions make nacreous clouds a rare, high-latitude phenomenon. Scandinavia, Iceland and northern Canada are favourite places to see them. Sightings in the southern hemisphere are even more rare because there is so little land far enough south except for Antarctica.”

More info: Polar stratospheric clouds

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Noctilucent Cloud 

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 shining in Latin. They are most commonly observed in the summer months at latitudes between 50° and 70° north and south of the equator. They can only be observed when the Sun is below the horizon.
They are the highest clouds in the Earth’s atmosphere, located in the mesosphere at altitudes of around 76 to 85 kilometres (47 to 53 mi). They are normally too faint to be seen, and are visible only when illuminated by sunlight from below the horizon while the lower layers of the atmosphere are in the Earth’s shadow. Noctilucent clouds are not fully understood and are a recently-discovered meteorological phenomenon; there is no record of their observation before 1885.
Noctilucent clouds can form only under very restrictive conditions; their occurrence can be used as a sensitive guide to changes in the upper atmosphere. They are a relatively recent classification. The occurrence of noctilucent clouds appears to be increasing in frequency, brightness and extent. It is theorized that this increase is connected to climate change.

More info: noctilucent clouds | Noctilucent Cloud Observers  | Homepage of NLC time-lapse movies

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More strange cloud phenomena explained 


Sundogs 

Video of unusual cloud activity gives rise to online UFO speculation
Footage taken of a cloud behaving most unusually has gone viral online, and prompted speculation as to what, or who, may have caused the phenomenon | Story

Jumping Sundogs Over Thunderclouds
Image Credit: abrigatti, YouTube

Explanation: What’s happening above those clouds? In the past few years, videos have appeared on the web detailing an unusual but little known phenomenon: rapid light changes over clouds. Upon inspection and contemplation, a leading hypothesis for its cause has now emerged.
In sum, this hypothesis holds that a lightning discharge in a thundercloud can temporarily change the electric field above the cloud where charged ice crystals were reflecting sunlight. The new electric field quickly re-orients the geometric crystals to a new orientation that reflects sunlight differently. In other words, a lightning discharge can cause a sundog to jump. Soon, the old electric field may be restored, causing the ice crystals to return to their original orientation. To help this curious phenomenon become better studied, sky enthusiasts with similar jumping or dancing sundog videos are encouraged to share them.

Source: APOD 2011 Nov 8

Sun dogs (or sundogs), mock suns or phantom suns, scientific name parhelia (singular parhelion), are an atmospheric phenomenon that consists of a pair of bright spots on either side on the Sun, often co-occurring with a luminous ring known as a 22° halo. Sun dogs are a member of a large family of halos, created by light interacting with ice crystals in the atmosphere. Sun dogs typically appear as two subtly colored patches of light to the left and right of the Sun, approximately 22° distant and at the same elevation above the horizon as the Sun. They can be seen anywhere in the world during any season, but they are not always obvious or bright. Sun dogs are best seen and are most conspicuous when the Sun is close to the horizon.

Examples of Sundogs

SundogSundogs_South_Dakota.

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Have you heard of Pareidolia?

Man’s face seen in clouds before death – video


Lismore resident Marion Dawson says a photo of clouds that bear a remarkable resemblance to her late brother Gerry Wells gives her “goosebumps”. The photo was taken on January 9 at Ocean Shores, on NSW’s far north cost, at the same time as Mr Wells was flying overhead from Brisbane to Sydney to visit family and friends, the Northern Star reports.
Mr Wells, 62, died from a heart attack only a few days later on January 24.
Mr Wells, who lived in Brisbane, never saw the photo, which was taken by a former editor of the Northern Star, Russell Eldridge, and published in the paper on January 11.
It was only after Mr Wells passed away that a friend of his son saw the photo on the internet.
The family used the cloud photo in a leaflet handed out to people at his funeral.
Ms Dawson said they all got goosebumps when they saw the similarity.
She said she did not believe it was a coincidence that Mr Wells was flying to Sydney to catch up with family and friends while the photo was being taken below and that he still managed to get home to say goodbye to his wife one last time.
“I truly believe somebody greater than us knew this was about to happen,” she said. | 
Source

More info: Cumulonimbus clouds

Explanation: Pareidolia is a psychological phenomenon involving a vague and random stimulus (often an image or sound) being perceived as significant. Common examples include seeing images of animals or faces in clouds, the man in the moon or the Moon rabbit, and hearing hidden messages on records when played in reverse. Related to sound it’s called auditory Pareidolia.

More about Pareidolia >>

More examples of pareidolia

'Roman god cloud' cruises past Canadian cameraman - video face cloud deer cloud dancing clouds Cumulonimbus cloud3 Cumulonimbus cloud2 Cumulonimbus cloud Circumhorizontal arc

 

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Other Clouds


Haboob Cloud

haboob_eating_phoenixA haboob (Arabic: هَبوبhabūb “blasting/drafting”) is a type of intense dust storm carried on an atmospheric gravity current. Haboobs occur regularly in arid regions throughout the world.

They have been observed in the Sahara desert (typically Sudan, where they were named and described), as well as across the Arabian Peninsula, throughout Kuwait, and in the most arid regions of Iraq. African haboobs result from the northward summer shift of the inter-tropical front into North Africa, bringing moisture from the Gulf of Guinea. Haboob winds in the Arabian Peninsula, Iraq, Kuwait, and North America are frequently created by the collapse of a thunderstorm, while haboobs in Australia may be frequently associated with cold fronts. The deserts of Central Australia, especially near Alice Springs, are particularly prone to haboobs, with sand and debris reaching several kilometers into the sky and leaving up to 30 centimetres (1 ft) of sand in the haboob’s path.

The arid and semiarid regions of North America—in fact, any dry region—may experience haboobs. In North America the most common terms for these events is either dust storm or sandstorm. In the U.S., they frequently occur in the deserts of Arizona, including around the cities of Yuma and Phoenix;in New Mexico, including Albuquerque; and in Texas. During thunderstorm formation, winds move in a direction opposite to the storm’s travel, and they move from all directions into the thunderstorm. When the storm collapses and begins to release precipitation, wind directions reverse, gusting outward from the storm and generally gusting the strongest in the direction of the storm’s travel.

When this downdraft of cold air, or downburst, reaches the ground, it blows dry, loose silt and clay (collectively, dust) up from the desert, creating a wall of sediment that precedes the storm cloud. This wall of dust can be up to 100 km (62 mi) wide and several kilometers in elevation. At their strongest, haboob winds often travel at 35–100 km/h (22–62 mph), and they may approach with little or no warning. Often rain does not appear at ground level as it evaporates in the hot, dry air (a phenomenon known as virga). The evaporation cools the rushing air even further and accelerates it. Occasionally, when the rain does persist, it can contain a considerable quantity of dust. Severe cases are called mud storms. Eye and respiratory system protection are advisable for anyone who must be outside during a haboob. Moving to shelter is highly desirable during a strong event.

Haboob

 

 

 

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Volcano Cloud 

volcano cloud

Image: NASA

This spectacular photo of the eruption of Sarychev Volcano in the Kuril Islands, northeast of Japan on June 12 shows an interesting example of a pileus cloud. The ash plume appears to have a smooth white cap on it as it breaks through the cloud cover above.

This type of cloud is caused by strong, relatively fast upward motion. Situations where this occurs include quickly growing thunderheads, volcanic eruptions and even nuclear explosions. In each case, something pushes warm, moist air upward quickly.
“You can see them very commonly above thunderstorms storms, and that’s because the air is moving so rapidly up there that the air flow gets perturbed above it,” Breed said. “And as soon as it cools enough for a cloud to form, you get these cloud caps.”
Chuang says pileus clouds look similar to the smooth caps sometimes seen on top of cumulus clouds, which are actually ice caps.
“If you have very strong convection, pushing quickly and very high, it forms more of an ice cloud because it is high enough for the crystals to freeze,” Chuang said. “It’s nothing more mysterious than things freezing.”
Source 

Pileus (meteorology)

A pileus (/ˈpləs/; Latin for cap), also called scarf cloud or cap cloud, is a small, horizontal, lenticular 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 updraft at lower altitudes, acting upon moist air above, causing the air to cool to its dew point. As such, they are usually indicators of severe weather, and a pileus found atop a cumulus cloud often foreshadows transformation into a cumulonimbus cloud, as it indicates a strong updraft within the cloud.

Clouds that are attached to pilei are often given the suffix “pileus” or “with pileus”. For example, a cumulonimbus cloud with a pileus attached to it would be called “cumulonimbus with pileus”.

Pilei can also form above ash clouds and pyrocumulus clouds from erupting volcanoes (see the image to the right).

Pilei form above some mushroom clouds of high-yield nuclear detonations.

A sheet of altostratus cloud often is seen lower down in a cumulonimbus cloud, this is known as a velum cloud.

 


Mushroom Clouds

Castle Romeo

Castle Romeo

A mushroom cloud is a distinctive pyrocumulus mushroom-shaped cloud of debris/smoke and usually condensed water vapor resulting from a large explosion. They are most commonly associated with nuclear explosions, but any sufficiently energetic detonation or deflagration will produce the same sort of effect. They can be caused by powerful conventional weapons, like vacuum bombs, including the ATBIP and GBU-43/B Massive Ordnance Air Blast bomb. Some volcaniceruptions and impact events can produce natural mushroom clouds.

Mushroom clouds result from the sudden formation of a large volume of lower-density gases at any altitude, causing a Rayleigh–Taylor instability. The buoyant mass of gas rises rapidly, resulting in turbulent vortices curling downward around its edges, forming a temporary vortex ring that draws up a central column, possibly with smoke, debris, or/and condensed water vapor to form the “mushroom stem”. The mass of gas plus entrained moist air eventually reaches an altitude where it is no longer of lower density than the surrounding air; at this point, it disperses, any debris drawn upward from the ground scattering and drifting back down (see fallout). The stabilization altitude depends strongly on the profiles of the temperature, dew point, and wind shear in the air at and above the starting altitude.

 


 

More cloud  info:

WMO cloud classifications”. Retrieved 2012-01-23.pdf

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

Accessory cloud (WMO term supplementary feature) – cloud that is attached to and develops on body of main cloud.
Anvil (WMO supplementary feature incus) – the top flatter part of a cumulonimbus cloud.
Anvil dome (WMO supplementary feature incus) – the overshooting top on a Cb that is often present on a supercell.
Anvil rollover – (slang) circular protrusion attached to underside of anvil.
Arcus cloud (WMO supplementary feature) – arch or a bow shape, attached to cumulus, thick with ragged edges.
Backsheared anvil – (slang) anvil that spreads upwind, indicative of extreme weather.
Clear slot or dry slot (informal term) – an evaporation of clouds as a rear flank downdraft descends and dries out cloud and occludes around a mesocyclone.
Cloud tags (WMO species fractus) – ragged detached portions of cloud.
Collar cloud (WMO supplementary feature velum) – ring shape surrounding upper part of wall cloud.
Condensation funnel (informal term) – the cloud of a funnel cloud aloft or a tornado.
Altocumulus castellanus (WMO genus and species) – castle crenellation-shaped altocumulus clouds.
Cumulus (WMO genus) – heaped clouds.
Cumulus castellanus  – (informal variation of WMO genus and species cumulus congestus) cumulus with tops shaped like castle crenellations.
Cumulus congestus  (WMO genus and species) – considerable vertical development and heaped into cauliflower shapes.
Cumulus fractus  (WMO genus and species) – ragged detached portions of cumulus cloud.
Cumulus humilis  (WMO genus and species) – small, low, flattened cumulus, early development.
Cumulus mediocris  WMO genus and species) – medium-sized cumulus with bulges at the top.
Cumulus pileus (WMO genus and supplementary feature) – capped, hood-shaped cumulus cloud.
Cumulus praecipitatio (WMO genus and supplementary feature) – cumulus whose precipitation reaches the ground.
Cumulus radiatus (WMO genus and variety) – cumulus arranged in parallel lines that appear to converge near the horizon.
Cumulus tuba (WMO genus and supplementary feature) – column hanging from the bottom of cumulus.
Cumulus undulatus (WMO genus and variety) – cumulus displaying an undulating pattern.
Cumulonimbus  (WMO genus) – heaped towering rain-bearing clouds that stretch to the upper levels of the troposphere.
Cumulonimbus calvus  (WMO genus and species) – cumulonimbus with round tops like cumulus congestus.
Cumulonimbus capillatus  (WMO genus and species) – Cb with cirriform top.
Cumulonimbus incus  (WMO genus and supplementary feature) – Cb with anvil top.
Cumulonimbus mamma (WMO genus and supplementary feature) – Cb with pouch-like protrusions that hang from under anvil or cloud base.
Cumulonimbus pannus (WMO genus and supplementary feature) – shredded sections attached to main Cb cloud.
Cumulonimbus pileus (WMO genus and supplementary feature) – capped, hood-shaped cumulonimbus cloud.
Cumulonimbus praecipitatio (WMO genus and supplementary feature) – Cb whose precipitation reaches the ground.
Cumulonimbus tuba (WMO genus and supplementary feature) – column hanging from the bottom of cumulonimbus.
Debris cloud (informal term) – rotating “cloud” of debris found at base of tornado.
Hail fog (informal term) – a shallow surface layer of fog that sometimes forms in vicinity of deep hail accumulation, can be very dense.
Inflow band (informal term) – a laminar band marking inflow to a Cb, can occur at lower or mid levels of the cloud.
Inverted cumulus (informal variation of WMO supplementary feature mamma) – cumulus which has transferred momentum from an exceptionally intense Cb tower and is convectively growing on the underside of an anvil.
Funnel cloud (informal term) – rotating funnel of cloud hanging from under Cb, not making contact with ground.
Knuckles (informal variation of WMO supplementary feature mamma) – lumpy protrusion that hangs from edge or underside of anvil.
Roll cloud  (may be informal term for WMO genus stratocumulus or supplementary feature arcus) – elongated, low-level, tube shaped, horizontal cloud.
Rope – (slang) narrow, sometimes twisted funnel type cloud seen after a tornado dissipates.
Rope cloud (informal term) – A very narrow, long, sometimes meandering, cumulus cloud formation that is frequently visible in satellite imagery.
Scud cloud (informal term for WMO species fractus) – ragged detached portions of cloud.
Shelf cloud (informal term for WMO supplementary feature arcus) – wedge-shaped cloud often attached to the underside of Cb.
Stratus fractus (WMO genus and species) – ragged detached portions of stratus cloud.
Striations (informal term for WMO supplementary feature velum) – a groove or band of clouds encircling an updraft tower, indicative of rotation.
Tail cloud (informal term) – an area of condensation consisting of laminar band and cloud tags extending from a wall cloud towards a precipitation core.
Towering cumulus (TCu) (aviation term for WMO genus and species cumulus congestus) – a large cumulus cloud with great vertical development, usually with a cauliflower-like appearance, but lacking the characteristic anvil of a Cb.
Wall cloud (informal term) – distinctive fairly large lowering of the rain-free base of a Cb, often rotating.


More:

Image Album
List of Cloud Types
Clouds ABC.pdf
Weird, Rare Clouds and the Physics Behind Them
Local Weather Forecasts via Cloud Reading 
A cloud atlas with many photos and description of the different cloud genera

 

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