Before the 1950’s, very little was actually known about the severe storms that spawn the recurring vortexes known as tornadoes. Science knew that tornadoes formed out of some really nasty thunderstorms over land, but the complete set of mechanics that had to come together in a specific unique way to actually form a single tornado, wasn’t completely understood by the meteorologists of the day.
Most people who have seen a tornado up close and personal can tell you what it looked like and the devastation it caused, but to understand some of the mechanics of how one is formed, Weatherquestions.com’s explanation provides an excellent overview of the driving forces that bring about the formation of a tornado, and the two primary reasons are due to instability of the atmosphere, and wind shear.
“Instability refers to unusually warm and humid conditions in the lower atmosphere, and possibly cooler than usual conditions in the upper atmosphere. Wind shear in this case refers to the wind direction changing, and the wind speed increasing, with height. An example would be a southerly wind of 15 mph at the surface, changing to a southwesterly or westerly wind of 50 mph at 5,000 feet altitude.
This kind of wind shear and instability usually exists only ahead of a cold front and low pressure system. The intense spinning of a tornado is partly the result of the updrafts and downdrafts in the thunderstorm (caused by the unstable air) interacting with the wind shear, causing a tilting of the wind shear to form an upright tornado vortex. Helping the process along, cyclonically flowing air around the cyclone, already slowly spinning in a counter-clockwise direction (in the Northern Hemisphere), converges inward toward the thunderstorm, causing it to spin faster. This is the same process that causes an ice skater to spin faster when she pulls her arms in toward her body.”
In the early 1950’s, a Japanese professor by the name of Tetsuya Theodore Fujita was brought to the United States by a man named Horace Byers of the University of Chicago. Dr. Fujita immediately began to direct an intense study of thunderstorm activity to gain a further understanding of the elements which have to come together for a tornado to form. He came up with a concept that he coined “tornado families” to explain why some of the destruction paths in the aftermath of a severe thunderstorm tornado were so long. These tornado families, he determined, were individual tornadoes that formed out of the same severe thunderstorm.
On Palm Sunday, April 11,1965, one of the worst tornado outbreaks ever recorded in America injured 1500 unsuspecting individuals, and further claimed the lives of 271 people. Dr. Fujita conducted an intense damage analysis from thousands of aerial photographs, and from his observations he was able to determine that there was something unique about specific tornadoes. Based on the patterns of destruction, he came to the conclusion that those tornadoes causing the worst calamities didn’t consist of just one vortex; they had multiple vortexes. So, from that point forward these monsters of destructive force in the tornado family have earned the right to be named “multiple vortex tornadoes”.
What is a multiple vortex tornado?
According to absoluteastronomy.com, “A multiple vortex tornado is a tornado that contains several vortices rotating around, inside of, and as part of the main vortex. These multiple vortices are somewhat similar to eyewall mesovortices found in intense tropical cyclones. The only times multiple vortices may be visible are when the tornado is first forming or when condensation and debris is balanced enough so that subvortices are apparent without being obscured. They are responsible for most (if not all) cases where narrow arcs of extreme destruction lie right next to weak damage within tornado paths.” These vortices are formed by the same processes that formed the primary tornado.
The inner vortices intensify the tornadoes destructive power because they rotate at a much faster rate than the primary tornado itself. Information from Stormeyes.org indicates that “Suction vortices can add over 100 mph to the ground-relative wind in a tornado circulation. As a result, they are responsible for most (if not all) cases where narrow arcs of extreme destruction lie right next to weak damage within tornado paths.” There can be as many as 6 or 7 vortices inside of one monstrous tornado, but normally, only 2 to 5 will occur at the same time.
There is no method for accurately determining the actual wind speed of a multiple vortex tornado. The Fujita Scale, which was developed by Dr. Fujita, estimates what an actual tornadoes wind speed was based on the amount of destruction that’s involved. Wind speeds are estimated from 40mph in the least destructive tornadoes, to 379mph in the most destructive ones.
It really doesn’t matter how much mankind attempts to understand, or anticipate the possibility of a multiple vortex tornado forming within a congested or rural area. It really doesn’t matter how well new structures are built, or how well older ones are modified. The end result of a multiple vortex tornado will be the same; destruction of an unbelievable scale.