Cirrostratus Nebulosus

Above: Cirrostratus Undulatus

Cirrostratus Undulatus

Cirrostratus undulatus clouds form at high levels, generally above 16,000 feet above cold land or sea up to 30,000 feet above tropical areas.

What are cirrostratus undulatus clouds?

Cirrostratus undulatus clouds are large cloud formations found at high altitude levels that can cover the whole sky or large parts of it. They are caused by water particles being steadily sucked up to high altitudes where they turn into ice crystals. This needs a gentle breeze to propel the water particles and they are normally formed when there is no intervening cloud layer below.

What height are cirrostratus undulatus clouds found?

They can be found at any height above 16,500 feet; the key requirement is that the air must be below zero degrees to allow the ice crystals to form to give the classic cirrus or cirrostratus formation the chance to develop. Occasionally their formation can cause snow to fall, this is known as the Vega effect, but the snow rarely reaches the ground.

Classification of cirrostratus clouds

Being part of the cirrostratus family of clouds, cirrostratus undulatus is part of the Cs family and its particular classification is Cs Und.

How are cirrostratus undulatus clouds formed?

Cirrostratus clouds are formed by the advance of a warm front and a gentle lowering of air pressure. Light surface winds pull water particles up from the ground or the sea, and these fuse with dust particles to produce the necessary elements to form the cirrostratus clouds. Cirrostratus clouds are as their Latin name indicates large cloud formations. It takes a great deal of moisture to form them, as they occupy a large amount of the sky and sometimes completely cover it, turning the sky white, while at the same time allowing sunlight and moonlight through.

What do cirrostratus undulatus clouds look like?

Cirrostratus undulatus clouds have the following characteristics:

  • White appearance normally thin enough to allow the sun or moonlight to shine through


  • An undulating edge often looking like rolling small hills or sand on the sea shore after the tide has gone out


  • Have a hazy image that is not clearly defined

 How common are cirrostratus undulatus clouds?

They are quite rare as their formation requires specific weather conditions at high altitude. There needs to be a wind blowing at a fairly steady rate under or over the clouds, this causes them to effectively ripple as the wind passes and form the classical undulatus effect. Should the wind decrease a standard cirrostratus cloud formation will return and should it increase the cirrostratus fibratus effect will be seen as the cloud is broken up.

Where can I see cirrostratus undulatus clouds?

Cirrostratus undulatus clouds can be seen more or less anywhere in the world at all times of the year. You stand your best chance to see them when a warm front is approaching and the air pressure is gradually falling. Well, it cannot be guaranteed that you will be able to see this type of cirrostratus cloud, as it requires specific wind conditions at the high altitudes to cause the cirrostratus undulatus clouds to form.

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