Cloud photographs reward a closer look at the lower surface as well as the outline. Rounded pouches, rolling waves and smooth layers can give the sky very different textures.
Describe the visible feature first
Mamma refers to hanging pouch-like features beneath a cloud. It is a supplementary feature, not a separate universal storm type, and its appearance alone does not prove a tornado is forming.
Asperitas: a rough, wave-like underside
Asperitas, recognised in the International Cloud Atlas, describes a rough, wave-like cloud underside. The uneven surface can resemble an agitated sea viewed from below, adding a distinctive texture to the sky without constituting a separate cloud genus.
Compare the shape before judging the colour: sunset or artificial illumination can transform the mood without changing the underlying cloud feature.
Further information: WMO description of mamma · International Cloud Atlas
Explore more: another guide to distinctive cloud forms; lens-shaped clouds near mountains.
1. Mamma over Fort Worth, Texas
Lars Plougmann’s image introduces the pouch-like underside commonly called mammatus. In the International Cloud Atlas, mamma is a supplementary feature that can occur with several cloud genera. It is not a separate kind of storm.
The rounded forms give the lower surface a strong texture. Looking at their edges and the shadows between them is more informative than deciding that the photograph must show a tornado developing. A cloud feature and a severe-weather warning are different forms of information.

2. Lenticular cloud near Mount Fuji, Japan
The smooth outline contrasts with the hanging pouches in the first image. A lenticular form can appear almost stationary near terrain even while air passes through the conditions that maintain it. The visual resemblance to a solid lens explains the name.
The mountain in the frame provides a reference for apparent position, but a still image does not establish the exact distance between summit and cloud. It also cannot supply a full wind profile. The photograph is best read as an example of form in a named setting.

3. Asperitas over Canterbury, New Zealand
The wittap photograph was originally described using the proposed term undulatus asperatus. Asperitas is now included in the International Cloud Atlas. The lower surface resembles a rough, uneven sea viewed from below, rather than an orderly set of parallel bands.
Asperitas describes the rough wave-like form, while light and cloud thickness influence how bright or dark it appears. The same underlying texture can therefore look very different across photographs. Colour contributes to the atmosphere of a scene without replacing the structural feature used in its identification.

4. A roll cloud in Queensland, Australia
The Mark Watson image connects a long horizontal cloud with a gliding scene. The modern Atlas describes the detached, tube-like roll form as volutus. Its separation from other cloud is an important distinction from a shelf attached to a larger cloud system.
The presence of a glider does not turn the image into aviation guidance. It illustrates the scale and shape of the feature within this particular photograph. The aircraft, cloud and horizon provide visual references, while actual flight decisions require information far beyond the image.

5. Mamma over Quebec, Canada
Michel Filion’s photograph returns to the pouch-like underside seen in Texas. Repetition within the gallery is useful when the surrounding setting and light differ. It lets readers recognise a similar structural feature without expecting every example to have identical colouring or contrast.
The Canadian scene provides another view of pouch-like forms beneath the cloud. Their spacing, depth and illumination differ from the neighbouring photographs, showing how the same feature can create a varied pattern rather than one uniform underside.

6. Shelf cloud in North Dakota
The Michael Carlson photograph shows the kind of low, broad feature described in the source as a shelf cloud. The important visual relationship is with the larger cloud mass and the horizon, not simply the fact that the shape extends horizontally.
A shelf cloud’s connection with surrounding cloud differs from the appearance of a detached roll. A wider composition can make that relationship easier to recognise than a tight crop. The visible structure helps with identification, although the photograph does not establish the full local weather conditions.

7. Nacreous clouds near McMurdo Station, Antarctica
The Alan R. Light image introduces a different atmospheric setting from the ordinary lower clouds elsewhere in the collection. Nacreous clouds are associated with the polar stratosphere. Their luminous appearance should not lead them to be confused with the noctilucent clouds shown later.
The two names describe different phenomena at different atmospheric levels. A colourful photograph by itself is not enough to identify either. The supplied McMurdo location and source description therefore remain important parts of how the image is understood.

8. Lenticular forms near Mount Rainier, Washington
Tim Thompson’s photograph provides another mountain-linked lens form. Compare its outline and apparent layering with the Mount Fuji image rather than assuming the two must show exactly the same local conditions. A similar visible shape can occur in different landscapes.
The mountain gives the cloud a strong point of reference. From this angle the two appear closely aligned, but the image compresses their three-dimensional relationship into one view. The terrain’s outline and the cloud’s smoother form create the central contrast.

9. Cumulonimbus near Nelson, British Columbia
Robert Neufeld’s image shifts attention from a cloud’s underside to its vertical development. A tall thunderstorm cloud is a different scale of classification from a supplementary feature such as mamma. That distinction helps make the whole collection easier to read.
A tall thunderstorm cloud does not automatically establish a supercell. That term concerns an organised storm structure, including a persistent rotating updraft. The photograph shows vertical development, while the additional dynamics require observations beyond height alone. A striking tower can therefore be described without assigning every possible storm classification to it.

10. A lenticular “UFO” in Patagonia
The smooth lens-like cloud resembles a hovering object, which explains the playful UFO comparison. Its apparent separation from the ground makes the shape especially conspicuous. As a lenticular example, it belongs with the other lens forms in the collection rather than with evidence of an aircraft.
Comparing this image with the Fuji and Rainier scenes shows how a similar outline can look different with another background, light direction or viewpoint. The atmospheric subject remains the cloud, while the imagined object is a human interpretation of its shape.

11. Shelf cloud over Cape Cod, Massachusetts
Anthony Quintano’s photograph gives the shelf-cloud theme a coastal setting. Its broad edge can be compared with the North Dakota image, but the location alone does not establish the same weather process in every detail. The photograph captures the scene at one moment in the storm's development.
Look at how the feature relates to the larger cloud behind it and to the horizon below. Those relationships are more useful for visual comparison than colour alone, which can change substantially with sunlight and camera exposure.

12. Altocumulus seen from the International Space Station
The image credited to cosmonaut Fyodor Yurchikhin and the Russian Space Agency changes the viewpoint dramatically. Clouds normally seen from below become a patterned surface viewed from above. The rounded or rolled elements can be compared across a much wider area.
The orbital viewpoint changes how cloud patterns are seen. Instead of looking up at an underside or along a horizon, the observer looks across their upper surfaces and wider arrangement. Familiar forms can therefore appear quite different from their ground-level equivalents.

13. Mamma over Manhattan, New York
The Skellig2008 image places the pouch-like cloud surface above a city. Buildings provide a recognisable foreground and help the viewer judge how much sky the feature occupies. The urban setting does not change the meaning of mamma.
This is another opportunity to compare structure across photographs: similar rounded forms appear in different surroundings. The city lights, skyline and exposure can affect the mood of the image without making it a different cloud feature or a prediction of a particular local hazard.

14. Noctilucent clouds over the Tibetan Plateau
The NASA Goddard-attributed view introduces high, night-shining clouds rather than the much lower weather clouds familiar from everyday skies. These clouds remain illuminated after the Sun has moved below the observer’s horizon. That lighting geometry is central to their visibility.
They should not be grouped with nacreous clouds merely because both can look unusual at twilight. The names refer to different upper-atmospheric phenomena. The location and agency caption help establish what the image was intended to show, while the photograph alone cannot measure its height.

15. Morning Glory clouds in Queensland
Mick Petroff’s photograph gives the long roll-cloud theme a named regional example. Morning Glory observations are associated with the Gulf of Carpentaria and Burketown. Those place names make the entry more specific than a generic description of a cloud cylinder.
Gliding is part of the history of observing this feature, although a photograph cannot provide the conditions needed for flight planning. The visual subject is the extended cloud form and its relationship to the landscape below.

16. A lenticular form near Palm Springs, California
The Palm Springs image is identified as a lens-like cloud form, with a narrow extension that inspired the description “funnel”. That resemblance alone does not establish a tornado. The surrounding smooth form remains central to the identification supplied with the photograph.
This entry is useful alongside the other lenticular images because a particular viewing angle can make the same general family of shapes look pointed, stacked or elongated. The full photograph provides more context than a cropped silhouette would.

17. Fog bow near Sydney, Australia
Nina Matthews Photography’s image adds an optical phenomenon rather than another cloud genus. A fog bow is associated with very small droplets and can appear much paler than a familiar rain rainbow. A fog bow is an optical effect, which makes it a different kind of subject from the cloud forms elsewhere in the collection.
The bow’s pale appearance depends on the interaction of light, droplets and the observer’s position. Its faint colour is part of the optical effect rather than evidence that the image has necessarily been desaturated. The arc gives an otherwise subtle scene a clear shape.

18. Shelf cloud near Wagga Wagga, Australia
Bidgee’s photograph adds another shelf-cloud view to the collection. Its landscape and lighting differ from the preceding examples, showing how the same broad feature can occupy a new visual setting. The photographed form provides the comparison, while an exact storm date is not established by its appearance.
A single still view does not show the whole development of the system. Readers can study the edge and its attachment to surrounding cloud while recognising that wind, rainfall and movement require observations beyond the frame.

19. Waterspout near the Balearic Islands, Spain
The Vvillamon image adds a rotating column over water. This is not simply another decorative cloud outline. The visible funnel is largely condensed droplets, so it should not be explained as a solid tube of seawater being pulled into the sky.
The waterspout image shows a rotating feature within its coastal setting. A still view cannot establish all the dynamics of the event or how it developed. Its shape and location provide the visible record, while a fuller classification would require additional observations.

20. Mamma near Norman, Oklahoma
Angelyn Hobson’s image closes the collection with a dramatic illuminated underside. The pouch-like structure links it back to the first entry, creating a useful visual circle across twenty scenes. The lighting gives the photograph character without changing the basic feature being described.
The collection brings together cloud genera, supplementary features, species and phenomena involving light or rotation. Those categories answer different questions about the sky. Recognising their roles makes the photographs easier to understand: a texture on a cloud’s underside is not the same kind of label as the cloud’s overall form.

Sources, photography and further reading
Original feature and image attributions:
- Clouds
- atmosphere
- lakes
- Lars Plougmann
- Japan
- Lenticular clouds
- New Zealand
- wittap
- Australia
- Mark Watson
- Canada
- Michel Filion
- Michael Carlson – Photography
- Antarctica
- Alan R. Light
- Tim Thompson
- Robert Neufeld
- Patagonia
- Anthony Quintano
- Skellig2008
- NASA Goddard Photo and Video
- Mick Petroff
- °Florian
- Nina Matthews Photography
- Bidgee
- Vvillamon
- Angelyn Hobson
- Memolition
- Snow Roller: A Strange Meteorological Phenomenon
- 7 Epic Displays Of Lightning
- Super Slow Motion Lightning Strike. 1 second in 3 minutes
- WMO description of mamma
- International Cloud Atlas
- another guide to distinctive cloud forms
- lens-shaped clouds near mountains
Current reference information, checked 15 September 2026:




Undulatus asperatus (or alternately, asperatus) is a cloud formation, proposed in 2009 as a separate cloud classification by the founder of the Cloud Appreciation Society. If successful it will be the first cloud formation added since cirrus intortus in 1951 to the International Cloud Atlas of the World Meteorological Organization. The name translates approximately as roughened or agitated waves.
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