They are not related to truetornadoes, and may occur well in front of the storm. Gustnadoes are strong, very local spinning winds associated withthe gust front of a thunderstorm. Rotation in the cloud is less organised than in large rotatingstorms associated with most tornadoes, and the funnel usuallydoesn't touch down, when it would be classified as a weak tornado. They are associated withcooler days when convective activity is not as strong, andoccur with weak thunderstorms or growing cumulus clouds. They form in a rotating storm systemand are associated with a wall cloud, but often decay beforea tornado is born.īut once a dust cloud is visible below the funnel cloud, a tornado has, by definition, formed, as the dust cloudis clear evidence that the vortex associated with the funnel cloud has touched down.Ĭold air funnel clouds, probably more common in Canada, sitbetween landspouts and tornadoes. This photo, courtesy of NOAA and theKrausman family, shows a probable landspout in East Wenatchee,Washington.įunnel clouds are closely related to genuine tornadoes andmay develop into them. They are usually defined by swirling dust, may have a weakcondensation funnel reaching up to the cloud base, and can be quite destructive. They most commonly form under large, actively growing cumulus clouds or weak thunderstorms, but unlike tornadoes are not associated with a wall cloud or strongly rotating storms. More information on waterspouts can be found amongĪs the name implies, landspouts are the land-based equivalentof waterspouts. Rain, whichis often falling behind the spout, will kill a waterspoutby cooling the air around it, stopping convection and rotation. Thecolumn becomes ropy in appearance, and may bend. The final stages of a waterspout occur as the column loses contact with the warm water and rising air that formed it. Fairweather waterspoutsrarely exceed 100ft (30m) in diameter.Īpart from the spray at its base, the funnel is not composed ofwater, but is outlined by water vapour formed as pressure dropsand evaporative cooling occurs. Wind speeds within the spout are typically between 60 and 120 mph (95-195kph), strong enough to be destructive but not devastating.The height of the column is generally less than 300ft (100m),but can reach heights of 2000ft or 600m. The waterspout is now at its peak, and has commenced moving across the surface, generally slowly butspeeds up to 80mph (130kph) have been recorded. As rotation increases,spiral wind lanes extend outwards, and once wind speeds increaseenough, water is whipped up to form a small cloud at the base.Īs the spout grows a funnel develops and extends upwardstowards the cloud base. The first sign of a waterspout is a dark spot on the watersurface marking the beginning of a vortex. Unlike tornadoes, fair weather waterspouts grow from the bottom up. Often their development is associated with incoming colder air,- the waterspouts of the Great Lakes form this way when thewater temperature is at its peak in late summer and early fall. Waterspout, Florida Keys.Courtesy NOAA Photo Library Much of our knowledge of waterspouts comes from studies by Dr Joseph Golden of NOAA in the 1960s and 1970s, and one of his photos is reproduced here. These conditions occur frequently in theFlorida Keys, a prime spot for waterspout observation. They are less intense, and tend to form over warm bodies of water in association with rapidly growing cumulus clouds. The other, more common forms are Fairweather waterspouts. They are just as dangerous, form under a rotating storm or supercell, and like tornadoes are associated with a wall cloud. In fact some of them, the tornadic waterspouts, are tornadoes which either move over water from the land, or form over water. As their nameimplies they occur over larger bodies of water - lakes orstretches of sea - and have the typical funnel form of tornadoes. Waterspouts are perhaps the most familiar, and whenconditions are right they can be quite common. Have the fastest and most destructive winds of all, and they are discussed elsewhere.But there are several other members of the tornado family of fast rotating winds, usually not as destructive but still dangerous. Large scale weather systems like cyclones, hurricanes, and even closed high pressure systems have some development ofspiralling winds to them, strong and destructive in the case of Moving air has a tendency to spin - to form into a vortex. Waterspouts and other tornado look-alikes may precede or follow tornadoes.
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