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Cloud of the week - cumulonimbus

Photo: Wikimedia Commons

Photo: Wikimedia Commons

Jen Bartram
Digital News Editor

Wednesday, July 30, 2014, 11:37 GMT -

This week we are taking a look at the godfather of all of the clouds and the one that everybody remembers from their school days: the giant cumulonimbus.

Cumulonimbus clouds are the ones that produce thunder, lightning and hail, as well as very heavy bursts of rain, and so understandably many people refer to them as storm clouds.

A typical cumulonimbus cloud will begin life as a humble, fluffy cumulus cloud. On warm days, these clouds can grow to vast heights as the powerful warm air rises from the ground.

When a cloud like this reaches the stratosphere, the top of it flattens out like a lid. Strong upper-level winds then blow the top of the cloud for hundreds of kilometers, producing the classic ‘anvil top’ associated with a cumulonimbus.

A cumulonimbus cloud seen from above. Photo: NASA via Wikimedia Commons

A cumulonimbus cloud seen from above. Photo: NASA via Wikimedia Commons

The top of a cumulonimbus cloud is very cold and icy, whereas the cloud itself contains a lot of water droplets. Within the cloud, air moves up and down at the same time and as ice crystals from the top fall through the cloud, they can collide with water droplets and gradually form hail.

This internal turbulence of ice crystals and water droplets can give rise to very strong winds, lightning and even tornadoes.

Although the anvil shape is the classic sign, this can often be hard to spot if a cumulonimbus is directly above you. Signs to look out for are the sky turning very dark on a warm day, heavy, sharp showers (rather than persistent rain), hail and lightning.

Photo: Uli Feuermeister via Wikimedia Commons

Photo: Uli Feuermeister via Wikimedia Commons

Cumulonimbus facts

  • A cumulonimbus cloud can rise to 20km into the sky – that’s over 12 miles!

  • There is as much energy in a single cumulonimbus as there would be in ten atom bombs.

  • A single cumulonimbus can weigh up to one million tons.

  • Most cumulonimbus clouds are short-lived, lasting around an hour before ‘blowing themselves out’.

  • Cumulonimbus clouds can exist on their own or can form a multicell or supercell storm, and can last for hours or even days at a time.

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