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Storm Cloud Week: MondayCumulonimbus is the wild beast of the cloud world. The mighty storm cloud is the embodiment of the power that drives our atmosphere. It can breed thunder, lightning, and hail within its turbulent belly. The largest Cumulonimbus clouds reach over 10 miles (16 km) up into the atmosphere, making it the tallest of the main types of cloud. It is also the one that gives us the happy phrase ‘on cloud nine’. When the first edition of the cloud-classification reference book the International Cloud Atlas was published in 1896, Cumulonimbus was ninth in the list of the ten main types of cloud. To be on cloud nine, therefore, was to be on the tallest cloud. And given conditions within and beneath an atmospheric monster like this, up the top is probably the part of a Cumulonimbus to be on.A huge Cumulonimbus with an ‘overshooting top’ likely extending into the lower stratosphere, spotted over Bluff, Utah, US by Paul Martini (Cloud Appreciation Society Member 27,060).