Cloud Types
Definition of a cloud
The World Meteorological Organization International Cloud Atlas defines a cloud as a hydrometeor consisting of minute particles of liquid water or ice, or both, suspended in the free air and usually not touching the ground. It may also include larger particles of liquid water or ice as well as non-aqueous liquid or solid particles such as those present in fumes, smoke or dust.
The part of the atmosphere in which clouds are present is divided into three levels:
High, Middle and Low. The regions in which clouds occur influence their height.
Below is a quick guide to identifying the ten main cloud types
Description Of The Cloud Types
Altocumulus
Usually forms in patches or layers of rounded masses and is white or grey. You will find Altocumulus in the middle levels. Precipitation rarely occurs and if it does it is in the form of virga (rain that does not reach the ground).
Altostratus
Altostratus is usually a uniform layer of cloud, with a colour of grey to blue-green. Found in the middle levels. Altostratus formes when large air masses lift and cause invisible water vapour to condense and form into clouds.
Altostratus May produce light precipitation generally in the form of virga (rain that does not reach the ground).
Cirrus
Cirrus is found in the high levels and has a fibrous or silky appearance and is white. It usually appears as detached clouds in patches or narrow bands.
Cirrocumulus
Found in the high levels cirrocumulus forms from the transformation of Cirrus or Cirrostratus clouds. Still, it can also form from the reduction in the size of a layer, patch or sheet of Altocumulus cloud.
Cirrocumulus is made almost entirely from ice crystals.
Cirrocumulus appears as a thin white layer, sheet or patch made of ripples or grains which are more or less regularly arranged, with an apparent width of less than one degree.
Cirrostratus
Found in the high levels, cirrostratus has a smooth or fibrous appearance. Cirrostratus will partly or entirely cover the sky and is transparent. With the sun or moon at the right angle, it will produce a halo effect.
It is made mostly of ice crystals and can form when ice crystals fall from a cirrocumulus cloud, the spreading of cumulonimbus cloud anvil or from the thinning of an altostratus cloud.
Cumulus
Cumulus clouds have dense, sharp outlines and develop vertically in the shape of a tower, dome or mound. Cumulus clouds have a dark base and any part that has sunlight on it, is usually bright white.
The base of Cumulus clouds is usually found in the lower levels and depending on the vertical development. The cloud tops are located in the middle or high levels.
Cumulus clouds are detached from each other and are made mostly of water droplets.
Cumulonimbus
Cumulonimbus, which is commonly known as a thunderstorm cloud has considerable vertical development. It is heavy and dense, and it appears in the form of large towers or mountains. Once the fully formed the tops will be flattened and look like an anvil or half anvil depending on wind speed in the upper layers. The base which usually starts in the lower levels will generally be very dark with ragged clouds underneath it. The tops will extend to the middle and the upper levels.
Cumulonimbus clouds are made of water droplets and ice crystals. Within the cloud, there are large raindrops snowflakes and snow pellets, ice pellets or hailstones.
Stratus
Stratus clouds usually appear as a grey layer with a mostly consistent cloud base. Generally found in the lower levels and made from small water droplets. At low temperatures, stratus clouds may form from ice particles.
Depending on the thickness of the cloud, it may produce drizzle or snow.
Stratocumulus
Stratocumulus is a layered patch or sheet of cloud which looks white, grey or both. Its width appearance is more than five degrees.
Found mostly in the lower levels stratocumulus is made up of water droplets which may be accompanied by raindrops or snow pellets. Stratocumulus looks very similar to altocumulus, but due to its location in the lower layers, it looks larger and potentially smoother. The layers of stratocumulus are generally continuous and may have gaps, with the bottom of the cloud appearing uneven and sometimes displaying wrinkles.
Nimbostratus
Nimbostratus consists of a high concentration of water droplets, snow crystals and snowflakes in a mixture or individual form.
Nimbostratus is a dark cloud layer which appears grey, and it covers a wide area of the sky. Nimbostratus is found in the middle levels but can extend to the low and high levels of the atmosphere.
Nimbostratus will produce consistent rain and snow. Due to its density, it can block out direct sunlight.