The word tornado comes from Spanish language and means to twist or turn. A tornado is a whirlwind produced by atmospheric conditions, mainly extremely low pressure, during a severe thunderstorm. Tornados usually turn counterclockwise. They appear as funnel shaped columns of violently rotating winds that reach down from a storm and touch the ground. Although a tornado is not always visible to the eye, tornadic conditions can still be picked up on radar, or the tornado may become visible once debris and dirt are pulled into it.
A tornado may also be referred to as a funnel cloud, but this is technically not a correct term. While the two words are sometimes used interchangeably, a funnel cloud is different, not in its make up, but in the fact that it does not touch the ground. Another name that is often used to describe a tornado is twister, due to its violent twisting motion.
The tornado is one of the most unpredictable and destructive forces of nature, often destroying everything in its path. A tornado is usually preceded by severe storms, which may include lightning, high winds, and frequently hail. It can change course without notice, and is usually accompanied by a roaring sound, or as some describe it, the sound of freight train.
The Fujita Scale measures the strength or intensity of tornados and uses five categories to determine how damaging each storm is. An F-1 is considered moderate, F-2 significant, F-3 severe, F-4 devastating, and F-5 incredible. There is a designation for F-6 but it is considered inconceivable, with winds reaching over 319 miles per hour (or about 510 kilometers per hour).
While tornados can occur anywhere in the world, there are more tornados in the United States each year than in any other country. There is even a section of the U.S. called Tornado Alley, which reaches from the Midwest into the South. The United Kingdom seems to experience quite a few tornados as well, and Canada sees its share, although most Canadian tornados are classified in the F-1 category.