The USA has been called the “land of opportunity” and surely she has exclusive wonders; but as April 26-28, 2011 has shown, nature’s violent side has found a unique home in America as well. True, the USA is not alone in her share of tectonic movement and meteorological variations; but in one area Mother Nature slaps the American landscape unduly hard, tougher than any other place on earth – America’s Tornado Alley.
Tornado Alley
This swath of land across the Great American Plains, is an impact zone where cool northwestern Canadian air flows southeastward and warm moist Gulf of Mexico air flows due north. Simultaneously, cold high altitude jet streams, descending across the Rocky Mountains from west to east, combine with low altitude dry desert winds, climbing to the northeast out of Mexico. These vertical and horizontal wind and direction mixtures increase the rotational effect already imposed on the colliding Canadian and Gulf air masses along a region we call Tornado Alley.
Stretching from Minnesota and South Dakota in the north to Texas and New Mexico in the south, Tornado Alley carves out a modified L shape that cuts through western Wisconsin, Iowa, Nebraska, Kansas, eastern Colorado, southeastern Wyoming and western Oklahoma every spring and summer. There is a secondary lane (what pilots call nature’s pressure bulkhead region or affectionately the Tennessee Popcorn Belt) that jumps from the west Texas contour into an area mostly east of the Mississippi River. This bow-shaped line includes the states of Mississippi, Alabama, Tennessee, Missouri, southern Illinois, Indiana and Ohio. Of the 53 recorded level F5 storms in the USA mentioned below, only three have been outside these few states (two in Michigan in the 1950s and one in North Dakota in 1957.)
Tornadoes, Tornadoes Everywhere
According to tornado expert Sid Perkins in his Science News article "Tornado Alley, USA", published on May 5, 2002; America has an average of 1,200 tornadoes a year. Peter Tyson, editor in chief of NOVA argued in a 2004 TV special entitled "Tornado Country" that this total is 75% of all tornadoes on the planet; however, the reasoning both supports and contradicts his thesis.
Tyson maintains that the “climatological conditions in the Great Plains are unparalleled for spawning tornadoes” and therefore forces the USA to have a disproportionate number of the beasts. On the other hand, he maintains that “…very few nations even bother to record tornadoes” implying the total number is reportedly low, artificially raising the USA’s percentage.
Mr. Tornado Solves the Conundrum
Whether the percentage is lower or the raw numbers of tornadoes is higher than reported, this minutia is irrelevant according to Dr. Tetsuya “Ted” Fujita. In his June 1976 award winning paper, "Photogrammetric Analysis of Tornadoes, F. History of Suction Vortices", Fujita explains that the USA has undeniably the greatest percentage of the most violent localized storms on earth.
Known by meteorologists as Mr. Tornado and by pilots as Father Ted (for his discovery of what he called the “thundernose,” today’s microburst) Ted Fujita completely changed society’s view of the world of violent wind. Looking at damage patterns from the atomic blasts in Japan after World War II, Dr. Fujita used this knowledge to eventually design his now famous Fujita Tornado Scale, or F-Scale of measuring intensities of relative small cyclonic events. While the scale was modified in 2007 (EFS) the basic design and ranges remained the same. From the lowly F0 wind event to the inconceivable F6 monster*; Mr. Tornado measured damage patterns to determine the wind speed of any particular storm.
The Geography of F5 Tornadoes
However, Father Ted’s scale had one serious drawback. The F-Scale measured damage and thus if a tornado, with very high wind speeds touched down in an uninhabited area, it did little damage. This leads to different rankings for storms with similar wind speeds. According to professor Fujita, no damage equals a small tornado; but logically that does not mean it is a nonviolent event.
The great plains of tornado alley are a very sparse region, full of wide open spaces, large farms, ranches and grazing lands. Subsequently, the quantities of potentially violent storms (ranking low on the F scale but nonetheless packing powerful winds) far outnumber those that do strike urban areas causing great devastating (F4) or incredible (F5) damage.
However, even with these urbanization facts encompassing a large geographical area in mind, the raw numbers of intense storms, ranking F4 or higher, still greatly exceed all other planetary zones combined. From the spring of 1953 to April 27, 2011’s Alabama storm** (according to the National Weather Service’s Storm Prediction Center), the USA’s Tornado Alley zone has had 53 confirmed EF5 tornadoes, compared to 11 worldwide (including the most deadly 1989 Bangladesh tornado that killed 1300 people).
During a three-day period from April 26 to 28, 2011, the USA saw 211 tornadoes kill 340 people (and climbing) in the second worst outbreak in American history. Racing across the entire length of tornado alley, these super storms set new records. But as devastating and deadly as this outbreak was, tornadoes in this part of America are an annual rite of spring. Formed by the collision of winds from the Rockies and deserts of the southwest with cold dry and warm moist air from Canada and the Gulf, America’s Tornado Alley comes to life six months out of every year.
*The original F-Scale actually ranged from F0 to F12 (the speed of sound); however, Dr. Ted believed the F6 and above storm “would be difficult to distinguish from an F5.”
**The Birmingham storm is part of a series of super-storms. This particular cell may have originated in Tuscaloosa, while another F5 touched down in Smithville, Mississippi.
Frank W. Hardy - Frank has 36 years of airline experience navigating every ocean & continent. Flying 25,000 hours in 42 years presents a rare historical ...
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