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 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, and are often, but not always, a visual precursor to tornadoes. Funnel clouds are visual phenomena, but these are not the vortex of wind itself.
A needle-like funnel cloud, which may have been a tornadic circulation but was not yet visible as such and which did later develop to become a confirmed tornado, near Elie, Manitoba
A shear funnel extending from a cumulus humilis cloud, which was observed in northern Texas during the first VORTEX project.
A cold-air funnel in Amarillo, Texas
Cumulonimbus is a dense, towering vertical cloud, typically forming from water vapor condensing in the lower troposphere that builds upward carried by powerful buoyant air currents. Above the lower portions of the cumulonimbus the water vapor becomes ice crystals, such as snow and graupel, the interaction of which can lead to hail and to lightning formation, respectively. When occurring as a thunderstorm these clouds may be referred to as thunderheads. Cumulonimbus can form alone, in clusters, or along squall lines. These clouds are capable of producing lightning and other dangerous severe weather, such as tornadoes, hazardous winds, and large hailstones. Cumulonimbus progress from overdeveloped cumulus congestus clouds and may further develop as part of a supercell. Cumulonimbus is abbreviated Cb.
Cumulonimbus incus
A view from space of a silhouette of a cumulonimbus in the afterglow of the troposphere at Earth's horizon, below the blue afterglow of the ozone layer at the lower stratosphere.
Cumulonimbus calvus cloud in Monterrey, Mexico.
Cumulonimbus calvus