Monday, February 9, 2015

Whirlwinds or Dust Devils

     Whirlwinds or dust devils are quite common throughout the arid and semiarid environments of Utah. All that is required to produce a dust devil is moderate heating at the surface of the earth and some horizontal component of wind. Usually a temperature in the 80's (Fahrenheit) and 10-15 knot (12-17mph) winds are enough to do the trick. Dust devils are therefore almost always associated with fair, sunny weather during the warm half of the year.
     Because the above conditions can occur almost anywhere in Utah, one would expect dust devils to be reported almost all of the time in various parts of the state. But, in fact, 90% are reported in the western valleys (often called the "west desert") of the Beehive state. The reason for this is implied in the name often applied to these twisting winds. It is usually only in the drier west deserts that there is enough loose and dry earth materials at the surface to be lifted by the wind and therefore become visible at a distance. In urban areas along the Wasatch Front, the progress of a dust devil can often be traced by the pattern of flying papers and other debris.
     Utah's dust devils have been called "crypto-vortices" or "sneaky winds." On occasion, they have surprised unsuspecting roofers and construction workers in precarious positions. However, there are no reports of severe injuries due to Utah dust devils, and only a few accounts of damage to property, as noted below:
     On June 7, 1974, a 60 miles-per-hour whirlwind 75 yards wide struck a boat marina near the Great Salt Lake and damaged a sign, roof, and small boat.
     On August 5, 1985, a huge dust devil tore part of the roof off a business in Murray.
     On June 15, 1996, a large dust devil more than 30 feet wide and about 500 feet high moved across the southwestern part of Salt Lake County, and did minor damage to some out buildings.
On a few occasions, large whirlwinds have been reported in the area of huge thunderstorm clouds. These are probably associated with "mircoburst" or downdraft winds from convective clouds. Sometimes the dust raised by this brand of dust devil may extend several thousand feet to near the base of the cloud. This may account for a few of the "twisters" or tornadoes that sometimes become a part of the official weather reports in the public media.
     Generally speaking, the dust devil or whirlwind is a phenomenon that can be considered a fair-weather or warm-weather happening in Utah that is not particularly dangerous, and can bring a rather welcome relief to the routine of an otherwise uneventful summer afternoon.

This picture of a whirlwind was taken above Geneva Steel 
on July 13, 2005, by Lynnette Kerby of Provo, Utah

Much of the information for this section originally appeared in the copyrighted book Utah's Weather and Climate, edited by Dan Pope and Clayton Brough, in 1996. UCCW Directors have received permission from the copyright owners of this book to reproduce such information on its website and to revise and updated it where appropriate.

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