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Sky Watching: Cumulus Clouds

By: Chrissy Warrilow
Published: March 21, 2013

Cumulus Clouds

Cumulus Clouds

iWitness Weather

iWitness contributor PrairieMan sent this picture of a "cumulus convention" from Spokane, Wash. (iWitness/PrairieMan)

  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds
  • Cumulus Clouds

Throughout the world, one of the most favored clouds among skywatchers is the cumulus cloud. The puffy, fluffy, whimsical clouds add character to beautiful sunny days, yet they become quite dramatic when they grow into huge, stormy thunderheads.

Sky Watcher Chart

How They Form

The word "cumulus" is Latin for the word "heap.".When warm, moist air rises, water vapor eventually cools and condenses on particles (called condensation nuclei) into tiny water droplets. As the process continues, water droplets continue to accumulate upwards, creating heaps visible in the sky as white, fluffy clouds. Essentially, a cumulus-type cloud is a cloud that develops in a vertical direction from the bottom up.

With increasing vertical height, cumulus clouds are often associated with convection. Bases of these clouds are generally no more than 3,000 feet above the ground, but they can develop past the troposphere in both temperate and tropical latitudes. Cumulus clouds are classified as low yet vertically building clouds.

(MORE: Mammatus Clouds | 10 Spectacular Clouds)

A Cloud By Any Other Name

Cumulus fractus clouds are cumulus clouds that appear in irregular fragments, as if they had been shred or torn apart.

Cumulus humilis clouds are the so-called "fair weather" cumulus clouds. They exhibit little or no vertical development and generally have a flat appearance. Their growth is usually limited by a temperature inversion (or an increase in temperature with height), which is marked by the unusually uniform height of the clouds. Cumulus humilis clouds tend to be small and develop near the ground. 

Cumulus mediocris clouds are cumulus clouds that are characterized by moderate vertical development with upper protuberances. Cumulus mediocris clouds are medium-sized clouds that do not produce precipitation, but they can develop into towering cumulus or cumulonimbus clouds, which do produce precipitation.

Cumulus congestus clouds are strongly sprouting cumulus clouds with generally sharp outlines, often with great vertical development. These are rapidly growing cumulus clouds whose height exceeds their width. Also known as towering cumulus (or towering Cu), they may occur as tower-like clouds with distinctive cauliflower tops: the cauliflower top often mean showers below, but without the characteristic anvil of a cumulonimbus, the cloud remains classified as cumulus congestus. These clouds may produce abundant showers and may develop further into cumulonimbus.

Cumulonimbus clouds are vertically developed cumulus clouds, often capped by an anvil-shaped cirriform cloud called an incus. Well known as thunderstorm clouds, cumulonimbus clouds are frequently accompanied by heavy showers, lightning, thunder, and sometimes hail, tornadoes or strong, gusty winds.


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