Asperitas clouds spotted by Weather Watchers

Some great examples of asperitas (formerly known as undulatus asperatus) clouds were spotted on Monday in Derbyshire. What are these impressive, distinctively wavy clouds?

Asperitas clouds are not as common in the UK as other cloud types, and some describe the cloud as rare. While we don't see them on a daily basis, they are spotted a few times a year. With the advent of smartphones it is now easier for us to capture these formerly 'rare' events.

The World Meteorological Organisation is responsible for maintaining the official 'Cloud Atlas', a catalogue of all the cloud types around the world. A new cloud atlas is due for released on 23 March and if the asperitas cloud is listed it will be the first new named cloud since 1951. The last cloud to be named was cirrus intortus.

It is not exactly understood how asperitas clouds are formed, but like all clouds in the atmosphere, they are produced from wave-like motions - an up and down movement - in the sky.

The base of the clouds can be anywhere between 4,000 to 10, 000ft (about 1-2 miles or 1-3km). The clouds need an unstable atmosphere, where air can rise and sink quickly, allowing changes to happen rapidly.

Asperitas clouds are dark and stormy looking so it's not surprising to know that they have been seen before a thunderstorm. However, quite often there is no storm and the clouds usually disappear fairly quickly.