<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (October 2012) (Learn how and when to remove this template message) </Td> </Tr> <P> A funnel cloud is a funnel - shaped cloud of condensed water droplets, associated with a rotating column of wind and extending from the base of a cloud (usually a cumulonimbus or towering cumulus cloud) but not reaching the ground or a water surface . A funnel cloud is usually visible as a cone - shaped or needle like protuberance from the main cloud base . Funnel clouds form most frequently in association with supercell thunderstorms . </P> <P> If a funnel cloud touches the ground it becomes a tornado . Most tornadoes begin as funnel clouds, but many funnel clouds do not make ground contact and so do not become tornadoes . Also, a tornado does not necessarily need to have an associated condensation funnel--if strong cyclonic winds are occurring at the surface (and connected to a cloud base, regardless of condensation), then the feature is a tornado . Some tornadoes may appear only as a debris swirl, with no obvious funnel cloud extending below the rotating cloud base . </P> <P> In cloud nomenclature, any funnel - or inverted - funnel - shaped cloud depending from cumulus or cumulonimbus clouds is technically described as an accessory feature called tuba . The terms tuba and funnel cloud are nearly but not exactly synonymous; a wall cloud, for example, is also a form of tuba . </P>

When does a funnel cloud become a tornado