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Incus (inc) – Latin for ‘anvil’, these striated icy canopies grow to enormous heights above a cumulonimbus capillatus cloud, spreading out when they reach the limits if the troposphere, the lowest layer of the atmosphere in which most clouds and weather occur. They can become detached from the cumulonimbus cloud whilst still active, of left behind long after it has decayed. In this case it is known as cirrus spissatus cumulonimbogenitus. |
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Mamma (mam) – also known as ‘mammatus’, these udder-like protuberances form on the undersides of stratocumulus and cumulonimbus clouds or their anvils. They are caused by powerful downdraughts as pockets of cold air sink rapidly from the upper to lower parts of the cloud, reversing the usual convective process. |
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Virga (vir) – Latin for ‘rod’ and also known as ‘fallstreaks’, virga is rain, snow or hail that evaporates before reaching the ground as it passes through warmer or drier air. It is usually associated with high or medium level cloud such as altocumulus floccus. |
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Praecipitatio (pra) – Latin for ‘fall’, this term is applied to any cloud from which rain, snow or hail reaches the ground. Precipitating clouds are most commonly cumulonimbus, stratus, nimbostratus, altostratus and stratocumulus. |
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Arcus (arc) – Latin for ‘arch’, these menacing clouds form a shelf or roll of dense cloud ahead of an approaching cumulonimbus cloud. They are formed by downdraughts of cold air pushing up layers of warm air near the ground. |
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Tuba (tub) – also known as ‘funnel clouds’, these columns of rotating air form beneath cumulonimbus clouds, creating a tapered cone or funnel descending as a vortex beneath the cloud. They rarely reach the ground, but if they do are known as landspouts or waterspouts. These are weak features compared to tornadoes which are produced by large scale rotation of a supercell thunderstorm. |