Above: Cumulus


Cumulus clouds are often the sign of good weather and settled conditions, however if they develop into cumulonimbus clouds, you can expect conditions to change for the worse.

What are cumulus clouds?

Cumulus clouds are caused by convection where warm moist air rises from the ground and the moisture having collided with dust particles will form particles of water. These particles will condense and form the small cumulus clouds that will grow as the heat of the day drives more water particles upwards.

Types of cumulus clouds

  • Cumulus undulatus
  • Cumulus mediocris
  • Cumulus fractus
  • Cumulus humilis
  • Cumulus congestus
  • Cumulus praecipitatio
  • Cumulus radiatus
  • Cumulus castellanus
  • Cumulus heaped clouds
  • Cumulus pileus
  • Cumulus tuba

What height are cumulus clouds found?

Cumulus clouds can be found at varying heights, typically cumulus clouds have a cloud base of about 6,500 feet, but if there is high pressure they can form at 10,000 feet. If the air pressure is high and stable, they are unlikely to turn into the more powerful cumulonimbus clouds that can bring thunderstorms and heavy rain showers in a very short space of time.

Classification of cumulus clouds

Cu is the WMO classification of cumulus cloud. It has many sub-classifications depending on the type of cumulus cloud that is observed. These can range from the light formations that indicate good weather to those that indicate that the cumulus cloud will develop into cumulonimbus cloud and bring bad or extreme weather.  

How are cumulonimbus clouds formed?

Cumulus clouds are formed by small pockets of warm moist air rising into cooler air at higher altitudes. The rising moist air forms compact fluffy lumps of cloud that are blown along on the wind. Cumulus in Latin means heap and is a very apt description. Cumulus clouds can be small, known as cumulus humis to the towering cumulonimbus that will bring thunderstorms and extreme weather.

What do cumulus clouds look like?

Cumulus clouds have a variety of shapes that can be identified before they evolve into another form, perhaps the more dangerous cumulonimbus that can bring violent storms or sharp showers:

  • A cumulus cloud will have a level base and a lumpy upper structure.


  • Looking closely you will notice that the upper structure is in constant evolution and changes shape regularly


  • The higher the wind speed driving the cloud or the higher the ground temperature driving the expansion of the cloud will cause its structure to change more rapidly


  • Cumulus clouds are normally white in color indicating they do not hold to much intense water content but they can become grey with the threat of evolving into the more ominous cumulonimbus form.

How common are cumulus clouds?

Apart from in arctic region, cumulus clouds can be found practically anywhere, wherever there is a temperature difference between the sea or the ground and the air above there will be convectional and this will cause cumulus clouds to form. Where the ground is dry, for example in the desert, there will be no moisture and so no cumulus clouds will form.

Where can I see cumulus clouds?

Even if you are living in dry or arid conditions, cumulus clouds can be found as the wind blows the air towards high ground. Mountains will cause the air to rise and any moisture in the air will be turned into cumulus clouds as the air must rise to cross the mountains.

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