Tuesday 18 October 2011

Waterspout.

A waterspout is an intense columnar vortex  that occurs over a body of water and is connected to a cumuliform cloud. In the common form, it is a non-supercell tornado over water. While it is often weaker than most of its land counterparts, stronger versions spawned by mesocyclones do occur. Waterspouts do not suck up water; the water seen in the main funnel cloud is actually water droplets formed by condensation. While many waterspouts form in the tropics, locations at higher latitude within temperate zones also report waterspouts, such as Europe and the Great Lakes. Although rare, waterspouts have been observed in connection with lake-effect snow precipitation bands.A winter waterspout, also known as a snow devil, an icespout, an ice devil, a snonado, or a snowspout, is an extremely rare instance of a waterspout forming under the base of a snow squall. The term "winter waterspout" is used to differentiate between the common warm season waterspout and this rare winter season event. Very little is known about this phenomenon and only six known pictures of this event exist to date, four of which were taken in Ontario, Canada. There are a couple of critical criteria for the formation of a winter waterspout. Extremely cold temperatures need to be present over a body of warm water enough to produce fog resembling steam above the water's surface; this requires a 19°C (34°F) temperature difference between the water and the invading surface air mass. Like the more efficient lake-effect snow events, winds focusing down the axis of long lakes enhance wind convergence and likely enhance their development.Waterspouts have long been recognized as serious marine hazards. Stronger waterspouts are usually quite dangerous, posing threats to ships, planes, helicopters, and swimmers. It is recommended to keep a considerable distance from these phenomena, and to always be on alert through weather reports. The United States National Weather Service will often issue special marine warnings when waterspouts are likely or have been sighted over coastal waters, or tornado warnings when waterspouts are expected to move onshore. When close to shorelines, waterspouts can devastate nearby coral reefs and marine organisms close to the surface.

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