A rotating, cone-shaped extension of cloud descending from a thunderstorm's base that has not yet reached the ground or a water surface; once it does, it is reclassified as a tornado or waterspout. A funnel cloud forms through the same low-pressure, rotating updraft dynamics as a tornado, made visible by condensation as air spirals inward and rises, and its presence signals conditions capable of producing a full tornado at any moment.
Facts
Identification
Distinguishing AppearanceA condensation funnel that extends downward from the base of a towering cumulus or cumulonimbus cloud, tied to a rotating column of air that has not reached the ground 1 PeriodicityFunnel clouds form most often in connection with supercell thunderstorms, the same rotating storm type that produces tornadoes 2 Connections
Associated With
A tornado is defined as a funnel cloud, or its associated ground-level circulation, that makes contact with the earth's surface; the two describe the same rotating column at different stages of one event.
Sources
1. NWS Glossary - Funnel Cloud
Glossary entry: funnel cloudQuote, Glossary entry: funnel cloud
A condensation funnel extending from the base of a towering cumulus or Cb, associated with a rotating column of air that is not in contact with the ground
2. Wikipedia - Funnel Cloud
Formation sectionQuote, Formation section
Funnel clouds form most frequently in association with supercell thunderstorms.
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