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Published: 07:31 EST, 14 March 2018 | Updated: 08:52 EST, 14 March 2018

WHAT IS A ROLL CLOUD AND HOW DOES IT FORM?

Roll clouds are horizontal and do not connect to the ground.

They are caused by a downdraft from an advancing storm causing moist warm air to rise, cool below its dew point and form a cloud.

When this happens uniformly along an extended front, a roll cloud may form.

The cloud species - similar to arcus - was last year officially named as a new species of cloud in the World Meteorological Organization's Cloud Atlas.

The new cloud species name will now be used by meteorologists operationally around the world.

The British Met Office and World Meteorological Organisation said it had made the decision after exhaustive research – with many pictures sent in by amateur cloudspotters around the world.

Going by the name volutus, the new species is described in the guidebook as 'long, typically low, horizontal, detached, tube-shaped cloud mass' and often appears to 'roll slowly about'.

The other subtype of arcus is a shelf cloud, which also often appear to precede storm fronts.

In March 11 new kinds of cloud were officially recognised by weathermen.

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