Cumulus cloud

Cumulus Cloud
Abbreviation	Cu
Genus	Cumulus (heap)
Altitude	Base below 2,000 m (below 6,500 ft) (tops vary)
Classification	low-level (family C) or vertical (family D), depending on size
Appearance	puffy
Precipitation cloud?	Depends. Cumulus humilis and mediocris, most likely no, but congestus, sometimes yes. Cumulonimbus, yes, but may be virga.
This box: view • talk

Cumulus clouds are a type of cloud with noticeable vertical development and clearly defined edges. Cumulus means "heap" or "pile" in Latin. They are often described as "puffy" or "cotton-like" in appearance. Cumulus clouds may appear alone, in lines, or in clusters. Cumulus clouds are often precursors of other types of clouds, such as cumulonimbus, when influenced by weather factors such as instability, moisture, and temperature gradient. Cumulus clouds are part of the larger family of cumuliform clouds, which include cumulus, cumulus congestus, and cumulonimbus clouds, among others.^[1]The most intense cumulus and cumulonimbus clouds may be associated with severe weather phenomena such as hail, waterspouts and tornadoes.

Formation

Cumulus mediocris from above

Cumulus clouds typically form when warm air rises and reaches a level of comparatively cool air, where the moisture in the air condenses. This usually happens through convection, where a parcel of air is warmer than the surrounding air.^[2] As it rises, the air cools at the dry adiabatic lapse rate (approximately 3°C per 1000 ft or 1°C per 100 m), while the dewpoint of the air falls by 0.5°C per 1000 ft.^[3] When the temperature of the air reaches the dewpoint, some water condenses out of the air to form the cloud. The size of the cloud depends on the temperature profile of the atmosphere and the presence of any inversion. If the top of the cumulus cloud reaches above the altitude where the temperature is at or below the freezing level, then precipitation from the cloud is possible.^[4] The temperature of the air at ground level will determine if this falls as rain or snow.

Simplified development of a cumulus cloud, given conditions are suitable.

In windy conditions, the clouds can form lines (cloud streets) parallel with the wind.^[5] In mountainous areas, they may also form lines at an angle to the wind, due to the presence of lee waves above the clouds.^[6]

Over the sea, cumulus clouds may be found in regularly spaced lines or patterns.^[7] The best examples of these lines are found in the trade winds, where they may extend for many miles^[vague]. Such lines create a pattern in the vertical movement of air, causing it to roll horizontally. Between the lines of cloud are stronger, more gusty, and slightly veering winds, but beneath the lines of cloud, somewhat lighter and more backing winds prevail.

The height at which the cloud starts to form (cloud base) depends on the amount of moisture in the air parcel that forms the cloud. Humid air will generally result in a lower cloud base.^[8] In temperate areas, the base of the cumulus clouds is usually up to 8,000 ft (2,400 m) in altitude. In arid and mountainous areas, the cloudbase can be in excess of 20,000 ft (6,000 m).

Glider pilots often pay close attention to cumulus clouds, as they can be indicators of rising air drafts or thermals underneath.^[5]

Forecast

Cumulus mediocris clouds above Rainbow Ridge in Red Rock Canyon, Las Vegas, NV.

Cumulus congestus cloud

Cumulus humilis clouds, appearing as small- or medium-sized puffy shapes in the sky, often occur in times of fair weather.^[9] However, cumulus clouds can grow into cumulonimbus clouds which may produce heavy rain, lightning, severe and strong winds, hail, and even tornadoes.^[10][11] Cumulus congestus clouds, which appear as relatively thin towers, will often grow into cumulonimbus storm clouds.

References

See also

• Clouds
• List of cloud types
• Turkey tower

External links

Wikimedia Commons has media related to: Cumulus clouds

• AMS Glossary of Meteorology
• Cumulus cloud at BBC Weather
• Cumulus cloud page at University of Richmond internal site
• Time-lapse of the formation of Cumulus clouds

Weather portal