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A waterspout near Florida.
A tornado is a violent windstorm characterized by a twisting, funnel-shaped cloud. The word "tornado" comes from the Spanish or Portuguese verb tornar, meaning "to turn." The phenomenon appears in storms all around the world, though they most commonly occur in a broad area of the American Midwest and South known as Tornado Alley, but some other countries see the storms occur in even higher densities.
Tornadoes develop from severe thunderstorms, usually spawned from squall lines and supercell thunderstorms, though they sometimes happen as a result of a hurricane. They are believed to be produced when cool air overrides a layer of warm air, forcing the warm air to rise rapidly, though tornadoes over water ( waterspouts) frequently are observed forming in the absence of convection or apparent strong surface temperature differences. Tornadoes are inextricably associated with lightningFor alternate meanings, see Lightning (disambiguation). Lightning is a powerful natural electrostatic discharge produced during a thunderstorm. Lightning's abrupt electric discharge is accompanied by the emission of light. The electricity passing through, and tornadoes (as well as dust devilDust Devil Johnsonville, South Carolina A dust devil is a small rotating updraft, at times 1000 meters or more high, but usually smaller, by an order of magnitude, and tens of meters in diameter. Dust devils are often observed in times of atmospheric turbs) exhibit enormous electromagnetic fields that are inexplicable by convection models. Many tornadoes appear at the tail end of mesocycloneMesocyclones are convection vortices formed in powerful thunderstorms, which generate many dangerous byproducts. They are most commonly observed in supercell thunderstorms, but they can drive the activity of lesser thunderstorms as well. A mesocyclone gens, coming from areas on radarThis article is about the device. For the fictional character in M A S H see Corporal Walter (Radar) O'Reilly. antenna (approximately 40m (130ft) in diameter) rotates on a track to observe activities near the horizon. Radar is an acronym for ra dio d etec screens that show a characteristic "hook echo".
The damage to human endeavours from a tornado is a result of the high wind velocity and wind-blown debris, as well as from electromagnetic effects, which frequently cause "freak" occurrences like wood impaling metal or stone, dried grasses (straw) impaling wood or animals and other similar effects inexplicable by fluid dynamics alone - there are some anecdotal accounts of fowl being entirely plucked of their feathers by tornadoes, which could be explained by static electricityStatic electricity or electrostatics is a field of science and a class of phenomena involving the imbalanced charge present on an object, typically referring to charge with voltage of sufficient magnitude to produce a spark. Generation The presence of cha effects. Tornado winds range from a slow 40 mi/h (65 km/h) at the low end to a possible 300 mi/h (480 km/h) in the strongest storms. Tornado season in North AmericaNorth America is the third largest continent in area and the fourth ranked in population. It is bounded on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the south by the Caribbean Sea, and on the west by the North Pacific Ocea is generally March through August, although tornadoes can occur at any time of year. They tend to occur in the afternoons and evenings: over 80 percent of all tornadoes strike between noon and midnight.
Tornadoes can be nearly invisible, marked only by swirling debris at the base of the funnel, though some nocturnal tornadoes have been observed glowing diffusely[1]. Retired U.S. Army captain Roy S. Hall and his family and others who have been inside tornadoes have reported[2] that the inside of tornadoes is very bright and flickering like a fluorescent light bulb. Verified observations by Hall and others suggest a cellular structure inside tornadoes. Some tornadoes are composed of several mini-funnels. A tornado must by definition have both ground and cloud contact.
The United States experiences by far the most tornadoes of any country, and has also suffered the most intense ones. However, tornadoes do occur throughout the world; the most tornado-prone region of the world, as measured by number of tornadoes per unit area, is the United KingdomThe United Kingdom of Great Britain and Northern Ireland is a state in Western Europe, usually known simply as the United Kingdom the UK Britain or less accurately as Great Britain . The UK was formed by a series of Acts of Union which united the formerly, especially England [3].
In Canada, an average of 80 tornadoes occur annually, killing 2, injuring 20 and causing tens of millions of dollars in damage. The last killer tornado in Canada struck Pine Lake , Alberta in July of 2000, killing 11.
On average, the United States experiences 100,000 thunderstorms each year, resulting in over 1,000 tornadoes and approximately 50 deaths per year. The deadliest US tornado on record is the March 18, 1925 Tri-State Tornado that went across southeastern Missouri, southern Illinois, and southern Indiana, killing 695 people. More than six tornadoes in one day is considered a tornado outbreak. The biggest tornado outbreak on record—with 148 tornadoes, including six F5 and 30 F4 tornadoes—occurred on April 3, 1974. It is dubbed The Super Outbreak. Another such significant storm system was The Palm Sunday Tornado Outbreak which affected the United States Midwest on April 11, 1965.
The intensity of tornadoes is given by the Fujita-Pearson Tornado Scale (also known simply as Fujita scale). The intensity can be derived directly with high resolution Doppler radar wind speed data, or empirically derived from structural damage compared to engineering data. Also, note that intensity does not refer in any way to the size, or width, of a tornado.
Trained weather spotters are often on alert to look for tornadoes and notify local weather agencies when severe weather is occurring or predicted to be imminent. In the United States, skywarn spotters, often local sheriff's deputies, fulfill this role. Additionally, some individuals, known as storm chasers, enjoy pursuing thunderstorms and tornadoes to explore their many visual and scientific aspects.
