In some parts of the world, waterspouts are a common sight. These twisting funnels of water are technically known as "convective vortices" and are similar to dust devils, which form over land. Most of the time, waterspouts occur on bodies of water with high surface temperatures, usually in tropical regions, larger forms include both tornadoes and hurricanes. The big spouts may generate vortexes of 100 mph or higher (160+ km/h). In the ocean around the Florida Keys, as many as 500 waterspouts form every summer, some of them of the larger variety. Farther north, drivers crossing the Tampa Bay Bridge are frequently entertained by the sight of these dancing funnels during the summer months. Waterspouts are also sometimes observed in the Great Lakes, along the Gulf Coast, and in the southern part of the Pacific Coast. Several have also bee noted on the Great Salt Lake in Utah.
Waterspouts form under
a variety of conditions, but are mostly associated with the growth phase of
cumulus congestus clouds. As a line of these clouds forms, waterspouts often
follow, sometimes appearing in groups. A waterspout, visible because of the
spinning spray of water that it is comprised of, usually extends from the surface
of a body of water up to the vase of the cloud aboveit, typically only a few
thousand feet (610m) above the surface. Often, the funnels formed by the smallest,
most common waterspouts twist and snake unevenly across this distance.
Depending on the amount of water in the funnel, all or part of the funnel may be observable, but in general, the closer to the water, the more visible the funnel. As they form, waterspouts often kick up a circular movement of water near the surface, making a ring of spray at the base of the spout, which appears larger than the funnel that extends out of it. This feature is called the spray sheath. Because of the long lines of visibility on the water, observers are often able to see the entire life cycle of a waterspout, beginning with the first signs of rotation on the surface. Waterspout funnels often grow in size as they "mature" and may form and reform more than once before dissipating. As spouts decay, they become thinner and fainter in appearance.
Most waterspouts are small, with this, ropelike funnels that may only be a few feet in diameter, but sometimes much larger spouts are generated. The big ones feature higher rotation speeds and large funnel diameters, sometimes as large as tornadoes. And just as tornadoes pack enough power to pose a threat to people and property, so too can large waterspouts produce damage and death, although this is rare.
On Lake Tahoe, high in the mountains in northern California --the elevation of the lake is 6,200 feet (1,890m)-- waterspouts are not common. In fact, waterspouts are so rare in mountain lakes that only a few have ever been recorded any where in the world. On September 26, 1998, however, the weather at Lake Tahoe featured a unique set of conditions ripe for the production of waterspouts. Gary Kaufman, a photographer living in the area, was lucky enough to be there at that time--with his camera ready--his interest piqued because of an earlier waterspout sighting on the same lake in 1981. In a period of several hours on that day, Kaufman observed and snapped multiple photographs of these rare Tahoe waterspouts.
These high-altitude twisters occurred between 7:00 and 9:30 A.M., forming and moving across the northern part of the lake. Several conditions combined to produce this event, although the exact set of circumstances is not known. One contributing factor may have been the surface temperature of the water--in the 60 degrees F (about 16 degrees C) -- but close to its peak temperature for the year in this high, cold environment. In these surroundings, the surface temperature rises due to the absorption of heat from the sun. At the same time cyclonic circulation in the atmosphere of the region helped converge moisture at a relatively low altitude-- related to an upper-level low--forming a line of cumulus congestus clouds and ideal conditions for the creation for waterspouts. Another potential factor may have been surface winds channeled by the local terrain around the shore of the lake.
A waterspout at Lake Tahoe is not only rare, the fact that there were at least six of these twisters observed makes it even more unusual. Stranger still, one of the spouts was of unusual size. This large funnel of vapor gradually expanded to be more than 250ft (76m) in diameter and could have been a serious threat if it had encountered any boats or structures on shore. Before this event, only about 12 waterspouts had been reported on Lake Tahoe in the previous 30 years. Thanks to Gary Kaufman, they now have a wider audience.
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