Weather Reference - Clouds - Cumulus

Location: London (Default) Lat: 51.5N Sunrise: 06:17GMT   Lon: 0E Sunset: 18:01GMT

Cumulus Congestus | Cumulus Mediocris | Cumulus Humilis | Pyrocumulus | Cumulonimbus Calvus | Cumulonimbus Incus | Cumulonimbus with Mammatus | Disclaimer

Cumulus Congestus

These clods are actively growing cumulus, sometimes vertical towers with ‘cauliflower’ tops.

They are powered by strong updrafts and can grow to an altitude of 15,000 to 20,000 feet. They are taller then they are wide and have a flat base and sharp outline.

They seldom form as a result of convection alone and normally atmospheric instability is also required. This occurs when the temperature of the surrounding air mass drops more than is normal, often as a result of cold air currents sliding over the cloud.

Cumulus Congestus is capable of generating heavy and prolonged showers of rain or snow.

Cumulus Mediocris

Cumulus Mediocris are of moderate depth, with restricted growing heads and are white or light grey. The cloud is normally as tall as it is wide.

It can begin to form from 2,000 feet upward depending on the surrounding humidity.

The clouds are more common in the late morning or early afternoon, after the ground has warmed enough to generate convection. These clouds are not large enough to generate precipitation.

Cumulus Humilis

These clouds appear to be flattened cumulus, much broader than they are deep and generally form as a result of ‘localised’ pockets of warm air rising. The water vapour in the air condenses into well defined, lumpy parcels of cloud at low level.

The base may start at around 2,000 feet but could begin at much higher levels in dry areas.

Because of the shallow depth, this cloud formation does not produce any significant weather.

Cumulus Humilis are widely distributed, occurring when conditions are right, except over Antarctica, where the cold surface temperature inhibits convection.

Pyrocumulus

The base of the Pyrocumulus can often be difficult to see as they are usually hidden by the smoke caused by the fire, however the top of the clouds will be visible.

This is a form of cumulus is present when a wildfire is present and get’s it’s name from the fact that fire creates both the lifting mechanism and the water vapour that combine to make this cloud.

Wildfire’s produce vigorous rising air currents and large quantities of water vapour that is released by the air and vegetation combustion. The rising air lifts the water vapour to a level where it condenses and forms cumulus clouds that rise above the fire.

Pyrocumulus can produce rain showers and if they grow large enough especially in subtropical regions can cause lightning strikes and even trigger further fires.

Cumulonimbus Calvus

A smooth, short lived cap of cloud above cumulus or cumulonimbus.

Once a cloud has reached the culvus stage, and if convection is still occurring and is enhanced by instability in the surrounding air mass, the cloud will continue to grow vertically. If the air speed is approximately 20 – 30 MPH the strong updraft will pick up a chunk of air and thrust it upwards. This causes the water vapour in the chunk to condense, and a smooth, elongated, cap like formation, known as pileus cloud appears above the calvus. As the calvus clouds continue to rise it gradually catches up with the pileus cloud. When the two clouds meet some of the pileus cloud topples off the side of the rising calvus.

Pileus clouds can produce thunderstorms.

Cumulonimbus Incus

Flattened anvil tops to cululonimbus that is made up of ice crystals.

Cumulonimbus Incus can reach over 60,000 feet in tropical and sub tropical areas and generally begin in the early morning as cumulus humilis then progress through the mediocris and congestus stages. For the cloud to develop at this point the process must combine with atmospheric instability to produce a powerful updraft.

If the air continues to be unstable the cloud will continue to ride and expand. Eventually the cloud reaches the top of the troposphere, where the air temperature levels off and begins to increase with altitude. This in effect places a lid on the updraft meaning that the cloud can not rise any further. As the air continues to push upwards, it spreads the clouds out.

This cloud can produce a severe storm, which may produce hail, strong wind gusts and even tornadoes.

Cumulonimbus with Mammatus

These are rounded pouches hanging from higher clouds.

This is one of the most spectacular of clouds and is associated with mature Cumulonimbus clouds, and is an indicator of severe weather conditions.

These clouds are formed because of a reverse direction convection. During a thunderstorm, warm, moist updrafts rise to the top of the troposphere where the temperature levels off and the air stabilizes. This causes the rising cloud to expand horizontally over areas of cooler, cloud free air. The temperature differences between the two air masses creates instability under the anvil, which causes pockets of warm, moist air in the cloud to convert downward. This reverse direction convection is enhanced by the effects of gravity and by precipitation from the cloud.

Cumulonimbus with Mammatus can spread over hundreds of square miles and is associated with tornadoes.

Because the formation is associated with mature cumulonimbus clouds, it is most likely to be seen from mid afternoon to early evening, when ground heating and associated convection activity has reached a maximum.

Disclaimer

All information is presented in good faith. We cannot accept any liability for any incorrect or incomplete information. You are strongly advised to seek clarification on any information presented. If you find any errors or omissions, please contact us to let us know so that we can put it right.