Gustnado

From Freepedia

A Gustnado is a type of short-lived cyclonic circulation that can form with severe thunderstorms. While it derives its name from the tornado, it has very little in common with tornadoes structurally.

Generally, severe thunderstorm winds (58 miles per hour and higher) are needed to generate gustnadoes. Damaging gustnadoes most often form in straight-line wind events and are more prevalent in thunderstorms with winds in excess of 100 miles per hour. They occur when rapidly descending air in a downburst or microburst interacts with the surface. The friction from this interaction forms spinning columns of air, or eddy currents, that can resemble tornadoes to the untrained eye, and can even cause tornado-like damage. To get a general idea of how gustnadoes form, one can picture an area of leaves swirling about on a windy day.

Gustnado circulations are thought to last, on average, no more than a few seconds to a few minutes each, although they may form, dissipate, and others reform so long as the thunderstorm can sustain its high winds.

A gustnado event occurred in Dickenson County, Virginia on July 4, 1997. A supercell thunderstorm formed near Clintwood, Virginia and raced across southwest Virginia at nearly 60 miles per hour. Along its path, wind speeds were estimated to be in excess of 100 miles per hour in some communities. Residents reported seeing tornadoes along the damage path, although most of the damage was of a straight-line nature. It is thought that gustnadoes formed in the downburst from this supercell storm.

A field survey confirmed localized pockets of tornado-like damage in the same path as the straight line wind damage. These smaller areas of tornado-like damage are thought to have been caused by gustnadoes. The storm had a nearly continuous damage path for over 100 miles before finally dissipating near Wytheville, Virginia. Template:Weatherstub