tornado

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tornado Funnel-shaped, violently rotating storm extending downwards from the cumulonimbus cloud in which it forms. At the ground its diameter may be only c.100m (310ft). Rotational wind speeds range from 160 to 480km/h (100 to 300mph). Tornadoes occur in deep low pressure areas, associated with fronts or other instabilities. They are most frequent in the Midwest and s USA.

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