Picture from NOAA
Copyright © 2007 by Ralph Couey
Written content only
Information for this article was taken primarily from “The Tornado” by Research Meteorologist Thomas P. Grazulis, who is the director of The Tornado Project, a private research and archive organization. Additional data was taken from the websites for the National Oceanographic and Atmospheric Administration (NOAA), The National Severe Storms Laboratory, and the National Weather Service.
Tornados are nature’s most violent windstorms. Born of powerful thunderstorms called supercells, their powerful winds and unpredictable nature pose a very real threat to life and property. According to the National Weather Service, the U.S. gets more tornados than any other country, around 1,200 per year. And while most seem to occur in Florida and the swath of Midwestern states known as ‘Tornado Alley,” all 50 states have experienced these storms. Anywhere supercell thunderstorms can form, the threat for tornados exists.
Hurricanes, in comparison, are enormous storms, covering thousands of square miles. But even the winds of the most powerful hurricanes ever recorded, Camille in 1969 and Allen in 1980, both 190 mph, were equal only to a medium-sized tornado.
The question of how and why tornadoes occur is still being investigated. Scientists know there are conditions within supercell storms common to tornado formation, but as to exactly what the actual trigger mechanism is, no one yet knows. Some supercells might spawn several tornados, while others with measurably identical parameters won't even form a single wall cloud.
Identifying and understanding that trigger mechanism also holds the key to determining how long a particular tornado might stay on the ground. Some have only touched down for a few minutes, while others might roar across the landscape for an hour or more. The infamous Tri-State Tornado of 1925 was reportedly on the ground for an incredible 219 miles across parts of Missouri, Illinois, and Indiana, leaving in its wake F-5 level damage and 619 dead. In recent years, meteorologists have begun to doubt that this was actually one tornado. In 1998, storm spotters recorded on video one instance where, as one tornado dissipated, another formed and strengthened within the same wall cloud. Although there were two separate twisters, the resulting damage path was uninterrupted. Some researchers suspect that this mechanism was at work in that Tri-State storm.
No one, not even an expert can rate a tornado by looking at it. There's simply too much variability in the twister's appearance to make such an assessment reliable or accurate. Tornados are rated according to the Enhanced Fujita Scale, which gauges storms based on a comprehensive damage assessment done after the tornado has passed. Such damage to a well-constructed frame home can range from shingles and windows for an EF-0 to complete obliteration in an EF-5.
