The Weather Briefing Cloud Atlas
Ten Principal Cloud Types
Clouds are classified by their family according to their height; low, middle, or high. Low clouds are based below 6,000 feet (2,000 meters), middle clouds are between 6,000 and 20,000 feet, and high clouds are above 16,500 feet (5,000 meters). The overlap in the middle and high clouds allow for variations in height at the top of the middle layer and bottom of the high layer. Clouds with great vertical extent through multiple layers are named according to the height of their bases. For example cumulonimbus or cumulus congestus clouds based in the low layer are low clouds.
Within each family clouds are characterized by their appearance; layered, heaped, or high thin and wispy. Layered clouds are a form of stratus, heaped clouds are a form of cumulus, and high thin wispy hair-like clouds are a form of cirrus. Stratus, Cumulus, and Cirrus are three of the ten principal cloud types.
For example, a low level cloud is found below 6,000 feet (2,000 meters) and is named according to its predominate shape; cumulus or stratus. Cumulus is heaped and stratus is layered.
Origin of today's Cloud Classification System
The grouping of clouds according to their appearance was first proposed by Luke Howard in 1803. Luke Howard was born in London, England in 1772 to successful businessman Robert Howard and his wife Elizabeth. He was educated as a Quaker at Burford in Oxfordshire and became an apprentice to a chemist in Stockport.
Howard became a business man, developing a company that manufactured pharmaceutical chemicals. His real interest was in meteorology, making several contributions to the subject besides his well known cloud classification system. The World Meteorological Organization adopted today's cloud classification system based on Howard's and published the International Cloud Atlas in 1956.
He coined the following cloud names, cirrus, cumulus, and stratus. He combined the names into, cirro-cumulus, cirro-stratus, cumulostratus, and cumulo-cirro-stratus or nimbus. His cumulostratus is now called stratocumulus and his cumulo-cirro-stratus is now just nimbus.
He published The Climate of London in 1818 with a second edition in 1830. He also presented seven lectures on meteorology (1837), the first in 1837, A cycle of eighteen years in the seasons of Britain (1842), and
Barometrographia (1847). He died in London on March 21, 1864. He was a member of the Royal Society and the Royal (now British) Meteorological Society.
Click on the photos below to see examples of the ten principal types.
This section is under construction.
Above 16,500 feet, (5,000 meters)
The cirrus Principal Cloud Type is made of various cirriform cloud elements which are white, delicate filaments, patches, or narrow bands. They appear as fibers and/or have a silky sheen. The ice crystal particles in cirrus are often large enough to have a significant speed of fall giving the cloud elements considerable vertical extent. Wind shear (variations in wind direction and/or speed) cause these fibrous trails to be slanted or curved. Cirrus elements are too narrow to cause a complete halo.
6,000 to 20,000 feet (2,000 to 6,000 meters)
Middle level clouds contain primarily water droplets. However, at sufficiently cold temperatures, ice crystals may be found in all forms of altocumulus, especially the species castellanus and floccus.
Below 6,000 feet (2,000 meters)
A Cumulonimbus with its base in the low levels is considered to be in the Low Family. If its base is in the middle levels it would be in the Middle Family. Note: The cumulonimbus in this photo has its base in the low levels which classifies it as a low cloud even though the top of the cloud is thousands of feet higher.
Photos Copyright, Craig Johnson, 2006 - 2019
How Clouds are Classified
Clouds are first identified by their form and height. The form is either layered, heaped, or wispy (hair-like). Their height is low, middle, high, or vertical. This is the cloud genera - one of 10 principal cloud types. Supplementary names are added to separate cloud types within the genera. These are the species and variety names. Two additional minor classifications are indicated below. When identifying clouds it important to remember that clouds don't always fit perfectly into our classification system. Dominate cloud types take precedence.
genera (genus) - the primary cloud characteristics, known as the ten principal cloud types
species - secondary characteristics determined by the shape and internal cloud structure
varieties - special characteristics that include the arrangement and transparency of clouds
supplementary features and accessory clouds - appended and associated minor cloud forms
mother-clouds - origin of clouds if formed from other clouds
Examples of Naming Combinations
Identify a cloud using its genera. Example: Cumulus
Primary cloud names are the cloud genera. Genera identify a cloud by family and form. Cloud families are based on cloud height; high, middle, or low. The basic cloud forms are cumulus and stratus. There are 10 primary cloud types known as the principal cloud types.
The 10 principal types are: Altocumulus, Altostratus, Cirrus, Cirrocumulus, Cirrostratus, Cumulus, Cumulonimbus, Nimbostratus, Stratocumulus, and Stratus.
Identify a cloud by its genera + species. This optional form of a cloud name adds a second level of description; the cloud shape and internal structure. For example: Altocumulus castellanus
Genera + species include: Cirrus fibratus, Cirrus uncinus, Cirrus spissatus, Cirrus castellanus, Cirrus floccus, Cirrocumulus stratiformis, Cirrocumulus lenticularis, Cirrocumulus castellanus, Cirrocumulus floccus, Cirrostratus fibratus, Cirrostratus nebulosus, Altocumulus stratiformis, Altocumulus lenticularis, Altocumulus castellanus, Altocumulus floccus, Stratocumulus stratiformis, Stratocumulus lenticularis, Stratocumulus castellanus.
Identify a cloud by its genera + species + variety. This optional form of a cloud name adds a third level of description; the cloud arrangement and transparency. For example: Cirrus fibratus vertebratus.
Genera + species + variety names include:
Fibratus pattern-based varieties
Cirrus fibratus intortus
Cirrus fibratus vertebratus
Pattern-based variety radiatus
Not all clouds have a species and/or a variety name. For example Altostratus has no species or variety name and Altocumulus floccus does not have a variety name.
Naming a Cloud
At first this process may seem confusing but breaking the naming process down into a few steps will make it easier.
First, It is correct to use only the cloud primary name (genera) as the cloud name. For example an altocumulus cloud may be identified by only its primary name; altocumulus. If there are additional characteristics the species name may be added to describe the cloud shape or structure; for example altocumulus castellanus (primary + species). If an additional description is desired the variety name describing cloud opacity, cloud structure, or overall cloud pattern may be added; such as altocumulus floccus undulatus (primary + species + variety).
When first learning cloud names it is advised you concentrate on using only the primary names. As you gain experience and become confident in your ability to name the primary cloud types you may add the species and eventually the variety names if you desire.
STEP 1 - The Primary Cloud Name
Is the cloud a high, middle, or low cloud and what is the shape of the cloud elements?
Determine the cloud height:
The best way to decide is to compare what you see with a photo of a similar looking cloud. The size and shape of cloud elements determine the primary name. Lower cloud elements appear larger than middle clouds and high cloud elements are smaller than middle clouds. Compare what you see with cloud photos on this website or other cloud photos that include cloud names. This takes practice.
Determine the shape of cloud elements:
Decide if the cloud is puffy/heaped (cumulus type) or flat/layered (stratus type). Cumulus cloud types often have vertical extent greater than horizontal extent, but not always. Stratus types have horizontal extent greater than vertical extent and display a definite layered or flat structure. Cirrus clouds are a special case. They are the highest cloud type, always higher than middle or low clouds. They may have three primary shapes; cumulus, stratus, or have a distinct wispy hair-like structure. Cirrus often display combinations of these shapes.
Cirrus are the highest clouds. All cirrus type cloud names begin with either "cirrus" or "cirro." Examples include "cirrus", "cirrostratus," or cirrocumulus. Middle clouds have the prefix "alto" in their name. Low clouds are either stratus or cumulus type. Clouds producing steady rain or snow reaching the ground use the prefix "nimbo." Clouds of great vertical extend (cumulonimbus) with their base in the low levels are considered to be low clouds. If the base is in the middle level they are considered to be middle clouds.
Cirrus, Cirrocumulus, Cirrostratus; Altocumulus, Altostratus; Cumulus, Cumulonimbus, Nimbostratus, Stratocumulus, and Stratus.
The primary cloud name is always one word.
STEP 2 - OPTIONAL - Species Name
This addition to the cloud primary name describes the cloud shape and structure. There are fourteen cloud species.
Weather Briefing Cloud Atlas
Above 16,500 feet (5,000 meters)
6,000 feet (2,000 meters) to 20,000 feet (6,000 meters)
Below 6,000 feet (2,000 meters)