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Cumulus Fractus Intortus — Hmm?

The weather page is prepared by Daniel Bezte. Dan has a BA Honours degree in geography, specializing in climatology, from the U of W. He has taught climate and weather classes at the U of W, and is a guest climate expert on CJOB’s morning show with Larry Updike. Daniel runs a computerized weather station on his 10 acres near Birds Hill Park, which he plans to develop into a small vegetable and fruit hobby farm.

Daniel welcomes questions and comments at [email protected]

In this article we’ll continue our study of clouds by looking at a number of additional terms that can be used to describe and help identify them, and we’ll also look at some rare or unusual cloud types.

Along with our 10 primary cloud types we can add a number of descriptor words to help describe all of the different variations of clouds that we can see. Here is a list of some (but not all) of these terms:

Capillatus – Cumulonimbus cloud with cirriform top.

Calvus – Cumulonimbus with puffy rounded top.

Incus – Cumulonimbus with flat anvil-like top.

Pileus – Small cap-like cloud over a cumulonimbus cloud.

Mammatus – Bag-like clouds that hang from the underside of the cloud.

Arcus – Low, horizontal cloud formation that precedes a thunderstorm.

Congestus – Moderate development and heaped into cauliflower shapes.

Fibratus – Thin fibrous-type clouds.

Fractus – A ragged, torn appearance.

Uncinus – Hook-shaped clouds.

Intortus – Clouds that appear all twisted up.

Lacunosus – Clouds with open spots and ragged edges.

Lenticularis – These clouds will have the shape of a lens – can look like a UFO.

Humilis– Cumulus clouds with flat bases and a little bit of vertical growth.

Undulatus – Clouds in patches, sheets, or layers showing undulations.

Translucidus – Clouds that cover the sky and are translucent enough to see the sun or moon.

Castellanus – Clouds with vertical development producing several towers of clouds which often look like small castles.

These descriptor words are usually added to the end of our main cloud type name. For example, if we have stratus clouds that have a ragged or torn appearance, we could call them Stratus Fractus clouds. If we see several cumulus clouds together growing vertically we could call them Cumulus Castellanus clouds.

Some of these cloud descriptor terms may be used on their own to identify clouds. A couple of examples of this would be Mammatus clouds, which we occasionally see with thunderstorms, or cumulonimbus clouds and Lenticular clouds, which are usually seen near mountains. In the case of Mammatus clouds, which can be associated with several of our main cloud types, they should be described technically with the main cloud type first and then the term Mammatus should follow it (ie. Cumulonimbus Mammatus), but most of the time you will simply see them reported or described as Mammatus clouds.

Lenticular clouds are named in a similar way. While we should name them as Altocumulus Lenticularis clouds or Cirrus Lenticularis (for example) we tend to simply group them all together as Lenticular clouds. One of the reasons for this is that these cloud types are fairly rare. The Lenticular clouds form when a smooth airflow rises up over a barrier (like a mountain) which causes a wave to form in the airflow. This is very similar to the wave formed when water flows over a rock. The part of the airstream that is forced upwards by the barrier cools and a cloud will form taking the shape of the wave. Then as the air sinks back down again the air warms and the water in the cloud evaporates and the cloud disappears. This results in a lens-shaped cloud that appears to stand stationary.

Mammatus and Lenticular clouds are not the only rare cloud types; we also have Nacreous clouds, or what is often called Mother-of-Pearl clouds. These clouds can be seen in northern countries when the sun is low on the horizon during the middle of winter. They are best visible in the early dawn or after dusk, because they are a very high cloud and are found high up in the stratosphere (rather than the troposphere), and at these times of the day they reflect sunlight from below the horizon making them visible.

If you are interested in all the different, unusual, and rare cloud types that are out there or if you just want to see some cool cloud pictures check out:

About the author

Co-operator contributor

Daniel Bezte

Daniel Bezte is a teacher by profession with a BA (Hon.) in geography, specializing in climatology, from the U of W. He operates a computerized weather station near Birds Hill Park.



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