Tornado Alley: What's that???
* Cooling off before late week warm-up: Full Forecast *
Notwithstanding a tardy beginning to the severe weather season this spring, the atmosphere has made up for lost time with destructive and deadly outbreaks of tornado generating thunderstorms for the past few days over much of the south and southeast U.S (here).
We generally expect a maximum in the occurrence of major tornado activity within a swath of the central U.S. colloquially referred to as "tornado alley" . Tornado alley is really just a nickname for the area of the relatively flat land in the Great Plains where warm moist air from the Gulf of Mexico clashes with cold air from Canada to generate conditions ripe for severe weather. But a new study suggests the greatest concentration of intense activity fall outside what's been traditionally considered tornado alley.
Keep reading for more discussion of tornado alley and actual storm activity...
There are several differing and sometimes inconsistent depictions of the geographical boundaries of tornado alley (here) depending upon how tornado occurrence is measured and differing databases over different time periods. (Note: there is no official National Weather Service (NWS) definition of the area delineating tornado alley)
An outstanding question is whether there is even justification for describing any single contiguous region as tornado alley (here)?
The latest contribution to this question (controversy?) is by Michael Frates of the University of Akron (Ohio) who sought to verify the existence of the "colloquial tornado alley" and to delineate other zones in the United States with high tornado activity. As reported by an article in Science News, Frates explored the distribution of F3 to F5 tornadoes with tracks 20 miles or longer over the southern and eastern U. S. from 1950 to 2006. A key distinguishing aspect of this study was its high spatial resolution and rigorous analysis techniques (quadrat analysis , Choropleth maps ).
Results from this analysis indicate the so-called "Tornado Alley" fails to represent the areas of most intense tornado activity in the United States. Surprisingly, the maximum number of intense tornadoes was found in what is referred to as "Dixie Alley", centered over Mississippi and northern Alabama. Frates also notes that tornadoes tend to strike Dixie Alley all year round, unlike the peak season in Tornado Alley being only four months long. Runner ups to these two top-prone areas in frequency of tornadoes occurred in Hoosier Alley (Indiana) and Carolina Alley.
Saturday's deadly twister in Mississippi is clear demonstration of the well-known fact that violent and killer tornadoes occur outside Tornado Alley every year. The study described here is an important contribution in defining regions subject to maximum danger and calling specific attention to the vulnerability in Dixie.
Beware, however, that dangerous tornadoes can occur almost anywhere in the U.S. including west of the Rockies and east of the Appalachians, and of course, the D.C. metro region. So, just in case, be prepared (caveat: if confronting a tornado while in a car, see, "Confusion on What to Do If Car Meets Tornado")
| April 26, 2010; 11:00 AM ET
Categories: Science, Thunderstorms, Tracton
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