A
funnel cloud (generally the cause of a twister or
tornado) 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.