Anyone who lives in the central United States is familiar with the term Tornado Alley. This is the region of the country where tornadoes are most likely to occur, the place where warm, humid air from the Gulf of Mexico collides with cool, dry air coming from Canada spawning the powerful storms that produce tornadoes. Tornado Alley encompasses much of the central region of the United States from North Dakota to Texas and east to Ohio and the western portions of Kentucky and Tennessee. This is where the most severe tornados form with the most frequency. Texas boasts the most tornadoes but Kansas and Oklahoma, second and third in numbers of tornadoes, actually have more tornadoes per land area. Florida has a large number of tornadoes but they are rarely of the intensity that occurs in Texas, Kansas, and Oklahoma.
Although Tornado Alley has the highest potential for deadly tornadoes, no state is free of tornadic activity. With changing climatic patterns, perhaps due to global warming, tornadoes are a risk throughout the United States. In fact, tornadoes have occurred on every continent on earth except Antarctica. Tornadoes can strike countryside, small towns, and major cities. They are not deterred from their paths by large urban areas. One of the most frightening potential situations is the destruction caused by a tornado in a major city.
Tornado Formation and Safety
The deadly twisting, funnel-shaped tornado descends from the base of a massive cumulonimbus cloud, a large thunderstorm cloud. This occurs when conditions are set for strong uplift of the warm moist air within the cloud. When warm moist air collides with a cold front with its cool dry air, atmospheric conditions become unstable, and incredible lifting occurs.
As the lifting brings wet air high into the cloud, rotation begins within the cloud. Tornadoes often accompany supercells where an area of rotation occurs several miles up into the atmosphere. These supercell thunderstorms spawn the most violent tornadoes. Tornadoes are brief and violent, but some storm systems can breed multiple tornadoes over the life of the storm.
Although science doesn’t fully understand the mechanisms of tornadic formation and action, these storms can be devastating in their intensity. Often coming with little or no prior warning, they wreak havoc when they strike. Even with the improvement of modern weather radar systems, there is still very little prior warning, so tornado-response plans must be made well in advance. Preparations include knowing well in advance where the safest place in the home, school, or office is. Interior rooms with no windows are preferable, but the safest spot is generally underground in a storm cellar or basement. Entire houses can be lifted off foundations leaving nothing but bathroom fixtures behind. If no other spot is available, an interior bathroom is the best choice. Cover heads with heavy pillows and crouch low in a corner to avoid flying debris.
Measuring the Strength of a Tornado
Since 1950, the National Weather Service has used the Fujita-Pearson Scale to measure the strength of a tornado. The lowest numbers represent the weakest tornadoes and the scale ranges from an F0 to an F6. An F0 tornado has winds of only 40-72 mph and does minor damage to trees, street signs, and chimneys. The next category is F1, capable of lifting a mobile home from its foundations. Wind speeds measure between 73 and 112 mph. F2 tornadoes are termed a significant tornado. With wind speeds of 113-157 mph it can do considerable damage to homes, lifting roofs and toppling trees. An F3 has powerful winds between 158 to 206 mph. With this kind of force, even well constructed homes can be severely damaged and most trees in the path are uprooted. An F4 tornado, capable of leveling a well-constructed house and turning airborne debris into deadly missiles, can flatten automobiles. Wind speeds for these devastating tornadoes range between 207 and 260 mph. During an F5 tornado houses are carried off their foundations and dropped a good distance away, cars-sized objects are thrown through the air, and the bark is pulled right off of trees. Skyscrapers can be severely damaged by an F5. Wind speeds accelerate to 318 mph. Thankfully never recorded, an F6 tornado could have wind speeds as high as 379 mph. This level of tornado is termed an inconceivable tornado and would cause total devastation.