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Cumulus clouds are a type of cloud with noticeable vertical development and clearly defined edges. Cumulus means "heap" or "pile" in Latin. 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. Cumulonimbus clouds may be associated with phenomena such as landspouts, waterspouts and tornadoes.

Formation Edit

Cumulus mediocris

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.[1] As it rises, the air cools at the dry adiabatic lapse rate (approximately 3°C per 1000ft or 1°C per 100m), while the dewpoint of the air falls by 0.5°C per 1000ft.[2] 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.[3] The temperature of the air at ground level will determine if this falls as rain or snow.


Simplified development of a Cu-cloud, given conditions are suitable.

In windy conditions, the clouds can form lines (cloud streets) parallel with the wind.[4] In mountainous areas, they may also form lines at an angle to the wind, due to the presence of lee waves above the clouds. [5]

Over the sea, cumulus clouds may be found in regularly spaced lines or patterns.[6] The best examples of these lines are found in the trade winds, where they may extend for many miles. 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.[7] In temperate areas, the base of the cumulus clouds is usually up to 8,000ft (2,400m) in altitude. In arid and mountainous areas, the cloudbase can be in excess of 20,000ft (6,000m).

Glider pilots often pay close attention to cumulus clouds, as they can be indicators of rising air drafts or thermals underneath. [4]


Cumulus humilis clouds, appearing as small- or medium-sized puffy shapes in the sky, often occur in times of fair weather.[8] However, cumulus clouds can grow into cumulonimbus clouds which may produce heavy rain, lightning, severe and strong winds, hail, and even tornadoes.[9] [10] Cumulus congestus clouds, which appear as relatively thin towers, will often grow into Cumulonimbus storm clouds.


  1. "BBC - Cumulus Clouds" (in English). Archived from the original on 2001-03-02. Retrieved on 2008-08-15.
  2. Brunt, D (1939). Physical and Dynamical Meteorology. London: Cambridge University Press. 
  3. Mossop, S C; Hallett J (November 1974). Ice Crystal Concentration in Cumulus Clouds: Influence of the Drop Spectrum: Science, AAAS. 
  4. 4.0 4.1 "Pilot Outlook - Cloud Streets" (in English). Retrieved on 2008-08-13.
  5. "Wave Soaring Over the British Isles" (in English). Retrieved on 2008-10-02.
  6. Russell, Sharman. "The Language of Clouds". Natural Resources Defense Council. Retrieved on 2008-10-14.
  7. "ARIC - Cumulus Clouds" (in English). Retrieved on 2008-08-16.
  8. "Michigan Tech - Cumulus Clouds" (in English). Retrieved on 2008-08-13.
  9. Palmer, Chad. "USA Today - Cumulus Clouds" (in English). Retrieved on 2008-08-13.
  10. Thompson, Philip; Robert O'Brien (1965). Weather. New York: Time Inc.. pp. 86–87. 

See also Edit

External links Edit


cs:Cumulus co:Cumulu da:Cumulusel:Σωρείτεςgl:Cumulusid:Awan Kumulus it:Cumulus he:קומולוס hu:Gomolyfelhő ms:Awan Kumulus nl:Cumulusno:Cumulus nn:Cumulus pl:Cumulus pt:Cumulus ro:Cumulus sk:Kumulus sl:Kumulus fi:Kumpupilvi sv:Cumulus vi:Mây tích uk:Купчаста хмара