Tornadoes



A tornado is a violent, rotating column of air which is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. The most intense of all atmospheric phenomena, tornadoes come in many shapes and sizes but are typically in the form of a visible condensation funnel, whose narrow end touches the earth and is often encircled by a cloud of debris and dust.

Most tornadoes have wind speeds between 40 mph (64 km/h) and 110 mph (177 km/h), are approximately 250 feet (75 m) across, and travel a few miles (several kilometers) before dissipating. The most extreme can attain wind speeds of more than 300 mph (480 km/h), stretch more than a mile (1.6 km) across, and stay on the ground for dozens of miles (more than 100 km).

Various types of tornadoes include the landspout, multiple vortex tornado, and waterspout. Waterspouts have similar characteristics to tornadoes, characterized by a spiraling funnel-shaped wind current that form over bodies of water, connecting to large cumulus and thunderstorm clouds. Waterspouts are generally classified as non-supercellular tornadoes that develop over bodies of water. These spiraling columns of air frequently develop in tropical areas close to the equator, and are less common at high latitudes.

Other tornado-like phenomena which exist in nature include the gustnado, dust devil, fire whirls, and steam devil.

Tornadoes have been observed on every continent except Antarctica. However, the vast majority of tornadoes in the world occur in the Tornado Alley region of the United States, although they can occur nearly anywhere in North America. They also occasionally occur in south-central and eastern Asia, the Philippines, east-central South America, Southern Africa, northwestern and southeast Europe, western and southeastern Australia, and New Zealand.

Tornadoes can be detected before or as they occur through the use of Pulse-Doppler radar by recognizing patterns in velocity and reflectivity data, such as hook echoes, as well as by the efforts of storm spotters.

There are several different scales for rating the strength of tornadoes. The Fujita scale rates tornadoes by damage caused, and has been replaced in some countries by the updated Enhanced Fujita Scale. An F0 or EF0 tornado, the weakest category, damages trees but not substantial structures. An F5 or EF5 tornado, the strongest category, rips buildings off their foundations and can deform large skyscrapers. The similar TORRO scale ranges from a T0 for extremely weak tornadoes to T11 for the most powerful known tornadoes.

A tornado outbreak sequence (or extended tornado outbreak) is a period of continuous or near continuous high tornado activity consisting of a series of tornado outbreaks over multiple days where there are very little or no days with a lack of tornado outbreaks. Major tornado outbreak sequences occurred in the United States in May 1917, 1930, 1949, and 2003. Another exceptional outbreak sequence apparently occurred during mid to late May 1896. Tornado outbreak sequences tend to dominate the tornado statistics for a year and often cause a spike in tornado numbers for the entire year. Read more ...

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In the News ...





What we know about tornadoes and climate change   CBS - March 6, 2019
The deadliest tornado to hit the U.S. in six years touched down in Alabama Sunday with winds of 170 mph and a path of 27 miles. It killed 23 people and was part of an early severe weather outbreak with 50 preliminary reports of tornadoes. At least 17 have been confirmed. But while some were quick to point to climate change as a cause of the tornado outbreak, current science isn't definitive about how much climate change influences tornadoes.




Is climate change making U.S. tornadoes worse?   PBS - March 5, 2019
When Americans hear the word tornado, their minds may bolt to huge twisters rolling across northern Texas, Oklahoma, Nebraska and Kansas, like a scene out of The Wizard of Oz. But the deadliest U.S tornado in six years didnŐt strike the Great Plains - instead, it touched down Sunday hundreds of miles away in Alabama and Georgia. On Monday and Tuesday, search crews, aided by dogs and drones, sifted through wreckage caused by the violent tornado, which blew across 30 miles with winds reaching up to 170 miles per hour. So far, the storm has killed 23 people, including three children, and dozens remain missing.




Tornadoes Don't Form Like Meteorologists Thought They Did   Live Science - December 14, 2018
Picture a tornado forming. Does the funnel cloud in your mind's eye reach down from the sky like a malicious, spindly finger? If so, that mental picture may be all wrong. New research suggests that tornadoes form not from the clouds down, but from the ground up. In a new study presented yesterday (Dec. 13) at the annual meeting of the American Geophysical Union in Washington, D.C., Ohio University meteorologist Jana Houser argued that of four tornadoes observed in enough detail with a rapid radar technique, not a single one started its rotation in the sky. Instead, Houser and her team found, the tornado rotation began rapidly near the ground




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