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The following is a glossary of tornado terms. It includes scientific as well as selected informal terminology.

A tornado is a rapidly rotating column of air that 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 windstorm is often referred to as a twister, whirlwind or cyclone, although the word cyclone is used in meteorology to name a weather system with a low-pressure area in the center around which winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern. Tornadoes come in many shapes and sizes, and they are often visible in the form of a condensation funnel originating from the base of a cumulonimbus cloud, with a cloud of rotating debris and dust beneath it. Most tornadoes have wind speeds less than 110 miles per hour (180 km/h), are about 250 feet (80 m) across, and travel a few miles before dissipating. The most extreme tornadoes can attain wind speeds of more than 300 miles per hour (480 km/h), are more than two miles (3 km) in diameter, and stay on the ground for dozens of miles.

Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric physics, with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw modest progress in the field after weather observation networks were formed across broad regions. Prior attempts at prediction of weather depended on historical data. It was not until after the elucidation of the laws of physics and more particularly, the development of the computer, allowing for the automated solution of a great many equations that model the weather, in the latter half of the 20th century that significant breakthroughs in weather forecasting were achieved. An important domain of weather forecasting is marine weather forecasting as it relates to maritime and coastal safety, in which weather effects also include atmospheric interactions with large bodies of water.

## A

The Advanced Radar Research Center (ARRC) is a University Strategic Organization of the University of Oklahoma (OU) located at the Radar Innovation Lab (RIL) in Norman, Oklahoma. The Executive Director of ARRC is Dr. Robert D. Palmer.

In the field of physics, engineering, and earth sciences, advection is the transport of a substance or quantity by bulk motion. The properties of that substance are carried with it. Generally the majority of the advected substance is a fluid. The properties that are carried with the advected substance are conserved properties such as energy. An example of advection is the transport of pollutants or silt in a river by bulk water flow downstream. Another commonly advected quantity is energy or enthalpy. Here the fluid may be any material that contains thermal energy, such as water or air. In general, any substance or conserved, extensive quantity can be advected by a fluid that can hold or contain the quantity or substance.

The American Geophysical Union (AGU) is a 501(c)(3) nonprofit organization of geophysicists, consisting of over 62,000 members from 144 countries. AGU's activities are focused on the organization and dissemination of scientific information in the interdisciplinary and international field of geophysics. The geophysical sciences involve four fundamental areas: atmospheric and ocean sciences; solid-Earth sciences; hydrologic sciences; and space sciences. The organization's headquarters is located on Florida Avenue in Washington, D.C.

## B

In fluid dynamics, the baroclinity of a stratified fluid is a measure of how misaligned the gradient of pressure is from the gradient of density in a fluid. In meteorology a baroclinic atmosphere is one for which the density depends on both the temperature and the pressure; contrast this with a barotropic atmosphere, for which the density depends only on the pressure. In atmospheric terms, the barotropic zones of the Earth are generally found in the central latitudes, or tropics, whereas the baroclinic areas are generally found in the mid-latitude/polar regions.

The Beaufort scale is an empirical measure that relates wind speed to observed conditions at sea or on land. Its full name is the Beaufort wind force scale.

In fluid dynamics, Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy. The principle is named after Daniel Bernoulli who published it in his book Hydrodynamica in 1738. Although Bernoulli deduced that pressure decreases when the flow speed increases, it was Leonhard Euler who derived Bernoulli's equation in its usual form in 1752. The principle is only applicable for isentropic flows: when the effects of irreversible processes and non-adiabatic processes are small and can be neglected.

## C

A capping inversion is an elevated inversion layer that caps a convective boundary layer.

The Center for Analysis and Prediction of Storms (CAPS) was established at the University of Oklahoma in 1989 as one of the first eleven National Science Foundation Science and Technology Centers. Located at the National Weather Center in Norman, Oklahoma, its mission is the development of techniques for the computer-based prediction of high-impact local weather, such as individual spring and winter storms, with the NEXRAD (WSR-88D) Doppler weather radar serving as a key data source.

A cold front is the leading edge of a cooler mass of air, replacing at ground level a warmer mass of air, which lies within a fairly sharp surface trough of low pressure. It forms in the wake of an extratropical cyclone, at the leading edge of its cold air advection pattern, which is also known as the cyclone's dry conveyor belt circulation. Temperature differences across the boundary can exceed 30 °C (54 °F) from one side to the other. When enough moisture is present, rain can occur along the boundary. If there is significant instability along the boundary, a narrow line of thunderstorms can form along the frontal zone. If instability is less, a broad shield of rain can move in behind the front, which increases the temperature difference across the boundary. Cold fronts are stronger in the fall and spring transition seasons and weakest during the summer.

## D

Tetsuya Theodore "Ted" Fujita was a prominent Japanese-American severe storms researcher. His research at the University of Chicago on severe thunderstorms, tornadoes, hurricanes, and typhoons revolutionized the knowledge of each. Although he is probably best known for creating the Fujita scale of tornado intensity and damage., he also discovered downbursts and microbursts, and was an instrumental figure in advancing modern understanding of many severe weather phenomena and how they affect people and communities, especially through his work exploring the relationship between wind speed and damage.

The University of Chicago is a private research university in Chicago, Illinois. Founded in 1890 by John D. Rockefeller, the school is located on a 217-acre campus in Chicago's Hyde Park neighborhood, near Lake Michigan. The University of Chicago holds top-ten positions in various national and international rankings.

A tornadic debris signature (TDS), often colloquially referred to as a debris ball, is an area of high reflectivity on weather radar caused by debris lofting into the air, usually associated with a tornado. A TDS may also be indicated by dual-polarization radar products, designated as a polarimetric tornado debris signature (PTDS). Polarimetric radar can discern meteorological and nonmeteorological hydrometeors and the co-location of a PTDS with the enhanced reflectivity of a debris ball are used by meteorologists as confirmation that a tornado is occurring.

## I

• In situ -
• Inflow -
• Inflow jet -
• Inflow notch -
• Instability -
• Institute for Disaster Research (IDR) -

## J

• Jet max (or jet maximum) -
• Jet streak -
• Jet stream -

## S

• Safe room -
• Satellite tornado - A smaller tornado that orbits a primary tornado associated with the same mesocyclone.
• Scouring - Term used when soil and dirt is pulled from the surface after a tornado.
• Scud (Scattered Cumulus Under Deck) -
• Severe local storm (SLS) - A thunderstorm presenting severe characteristics in a localized area.
• Severe Local Storms Unit (SELS) - A team of National Weather Service experts tasked with forecasting convective weather. It was eventually included as a unit within the NSSFC.
• Severe thunderstorm (svr) - A hazardous thunderstorm capable of causing injury or damage. The U.S. National Weather Service defines a severe thunderstorm as one producing 58 mph (93 km/h) or greater winds, 1 in (2.5 cm) or larger hail, or producing a funnel cloud or tornado.
• Shallow convection - Occurs when convective instability exists, but no convection occurs
• Shear - Wind shear - Winds aloft, often measured in knots.
• Shear funnel - Brief, often weak funnel generated by shear in a thunderstorm.
• Shelf cloud - Generally associated with strong thunderstorms, found along the leading edge. Horizontal and dark in appearance.
• Shortwave trough - Embedded kink within seen in overall troughing patterns.
• Significant tornado - A substantial tornado, one that is rated F2-F5 or EF2-EF5. Grazulis also includes (E)F0-(E)F1 tornadoes that cause a fatality in his definition for The Tornado Project database.
• Significant tornado parameter (STP) - Model parameter calculated using Shear values, Instability values, and vorticity values.
• Skywarn - The storm spotting program of the US National Weather Service. Skywarn organizations have also been formed in Europe. The Canadian program is Canwarn.
• Slight risk (SLGT) -
• Space Science and Engineering Center (SSEC) -
• Speed shear -
• Spin-up - A small, ephemeral vortex. These can refer to tornadoes spawned by quasi-linear convective systems or tropical cyclones, which occasionally become strong and fairly long track. A spin-up may sometimes refer to a landspout or gustnado (the latter of which is rarely an actual tornado).
• Splitting storm (or storm split) -
• Stability index -
• Stacked low -
• Steam devil -
• Storm chasing - Traveling with the intent to observe tornadoes and other severe weather.
• Storm interaction -
• Storm merger -
• Storm relative environmental helicity (SREH) or storm relative helicity (SRH) -
• Storm shelter -
• Storm spotting - The observation of severe weather by individuals trained in weather and reporting. Spotters can be stationary or mobile.
• Storm Data (SD) - A National Climatic Data Center (NCDC) publication beginning in 1959 detailing quality controlled tornado and other severe weather summaries as the official NOAA record of such events.
• Storm Prediction Center (SPC) - The NWS national guidance center that issues tornado, severe thunderstorm (straight-line wind and hail), and wildfire forecasts.
• Storm scale -
• Storm Track (magazine) (ST) - A science and hobby magazine on storm chasing published from 1977-2002.
• Stovepipe tornado - (slang) Storm chaser slang for a large cylindrically shaped tornado resembling a stovepipe.
• Straight-line wind -
• Streamline -
• Streamwise vorticity -
• Striations -
• Strong tornado - A tornado rated F2-F3, EF2-EF3, T4-T7, or at least as strong as F2, EF2, T4.
• Subsidence -
• Subvortex - A smaller constituent vortex within a (multiple vortex) tornado.
• Suction spot - Older term for a subvortex.
• Supercell (sup) -
• Supercell composite parameter (SCP) -
• Supertornado - (slang) A colloquial term used to refer to a tornado achieving the maximum of some measurement, such as a F5/EF5 tornado.
• Surface weather analysis -
• Surface weather observation -
• Synoptic scale meteorology -

## T

F0
EF0
F1
EF1
F2
EF2
F3
EF3
F4
EF4
F5
EF5
WeakStrongViolent
Significant
Intense
• Tail - (slang) A colloquial term for a tornado; most commonly used in the Southern U.S.
• Tail cloud -
• Temperature -
• Terminal Doppler Weather Radar (TDWR) -
• Thermal -
• Thermodynamics -
• Thunderstorm (tstm) -
• The Thunderstorm Project -
• Thunderstorm spectrum -
• Tilted updraft
• Tornado Alley - A colloquial term referring to regions where tornadoes are perceived as striking more frequently than other areas. It may also be referred to as a tornado belt, especially when describing smaller areas.
• Tornado climatology - The study of geographical and temporal distribution of tornadoes and causes thereof.
• Tornado Debris Project (TDP) -
• Tornado debris signature (TDS) - A more formal term for a debris ball.
• Tornado emergency - Enhanced wording used by the U.S. National Weather Service in a tornado warning or severe weather statement when a large, intense tornado is expected to impact a highly populated area (traverse a large city or dense suburbs).
• Tornado family - A series of tornadoes spawned by successive (low-level) mesocyclones of the same supercell thunderstorm in a process known as cyclic tornadogenesis. Multiple such supercells occurring on the same day in a common region results in a corridor outbreak of tornadoes.
• Tornado Force scale (TF scale) -
• Tornado Intercept Project (TIP) -
• The Tornado Project (TP) - A concerted research effort from the 1970s-1990s by Thomas P. Grazulis that compiled tornado information for risk assessment. TP published exhaustive accounts, tabulations, and analysis of all known significant tornadoes in the US from 1680-1995, which comprises one of three tornado databases.
• Tornado rating - A subjective integer value assigned to a tornado differentiating its intensity (or path length or width), typically as a proxy inferred by damage analysis.
• Tornado watch (TOA or WT) - A forecast that atmospheric conditions within a designated area are favorable for significant tornado activity over the next 1-6 hours (colloquially referred to as red box).
• Tornado warning (TOR) - A tornado is occurring or is imminent as one is sighted or is suggested by radar.
• Tornadocyclone - The parent circulation of a tornado. This nay refer to a low-level mesocyclone.
• TORRO (TORnado and storm Research Organisation) -
• TORRO scale - A tornado rating scale developed by Terence Meaden of TORRO classifying tornadoes in the UK from T0-T10 based on intensity.
• TOTO (TOtable Tornado Observatory) -
• Transverse rolls -
• Trigger - (slang)
• Tropical cyclone (TC) -
• Trough -
• Tube - (slang) A storm chaser term for a tornado.
• Turbulence -
• Twister - (slang) A colloquial term for a tornado. Also, a major theatrical film about storm chasing released in 1996.
• TWISTEX (Tactical Weather-Instrumented Sampling in/near Tornadoes EXperiment) -

## Related Research Articles

In meteorology, a cyclone is a large scale air mass that rotates around a strong center of low atmospheric pressure. Cyclones are characterized by inward spiraling winds that rotate about a zone of low pressure. The largest low-pressure systems are polar vortices and extratropical cyclones of the largest scale. Warm-core cyclones such as tropical cyclones and subtropical cyclones also lie within the synoptic scale. Mesocyclones, tornadoes and dust devils lie within smaller mesoscale. Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the tropical upper tropospheric trough during the summer months in the Northern Hemisphere. Cyclones have also been seen on extraterrestrial planets, such as Mars and Neptune. Cyclogenesis is the process of cyclone formation and intensification. Extratropical cyclones begin as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones. These zones contract and form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, extratropical cyclones occlude as cold air masses undercut the warmer air and become cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the subtropical jet stream.

A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are sometimes called thundershowers. Thunderstorms occur in a type of cloud known as a cumulonimbus. They are usually accompanied by strong winds, and often produce heavy rain and sometimes snow, sleet, or hail, but some thunderstorms produce little precipitation or no precipitation at all. Thunderstorms may line up in a series or become a rainband, known as a squall line. Strong or severe thunderstorms include some of the most dangerous weather phenomena, including large hail, strong winds, and tornadoes. Some of the most persistent severe thunderstorms, known as supercells, rotate as do cyclones. While most thunderstorms move with the mean wind flow through the layer of the troposphere that they occupy, vertical wind shear sometimes causes a deviation in their course at a right angle to the wind shear direction.

A supercell is a thunderstorm characterized by the presence of a mesocyclone: a deep, persistently rotating updraft. For this reason, these storms are sometimes referred to as rotating thunderstorms. Of the four classifications of thunderstorms, supercells are the overall least common and have the potential to be the most severe. Supercells are often isolated from other thunderstorms, and can dominate the local weather up to 32 kilometres (20 mi) away. They tend to last 2-4 hours.

A mesocyclone is a vortex of air within a convective storm. It is air that rises and rotates around a vertical axis, usually in the same direction as low pressure systems in a given hemisphere. They are most often cyclonic, that is, associated with a localized low-pressure region within a severe thunderstorm. Such thunderstorms can feature strong surface winds and severe hail. Mesocyclones often occur together with updrafts in supercells, within which tornadoes may form at the interchange with certain downdrafts.

A squall is a sudden, sharp increase in wind speed lasting minutes, contrary to a wind gust lasting seconds. They are usually associated with active weather, such as rain showers, thunderstorms, or heavy snow. Squalls refer to the increase to the sustained winds over that time interval, as there may be higher gusts during a squall event. They usually occur in a region of strong sinking air or cooling in the mid-atmosphere. These force strong localized upward motions at the leading edge of the region of cooling, which then enhances local downward motions just in its wake.

A squall line or quasi-linear convective system (QLCS) is a line of thunderstorms forming along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front. It contains heavy precipitation, hail, frequent lightning, strong straight-line winds, and possibly tornadoes and waterspouts. Strong straight-line winds can occur where the squall line is in the shape of a bow echo. Tornadoes can occur along waves within a line echo wave pattern (LEWP), where mesoscale low-pressure areas are present. Some bow echoes which develop within the summer season are known as derechos, and they move quite fast through large sections of territory. On the back edge of the rainband associated with mature squall lines, a wake low can be present, sometimes associated with a heat burst.

A wall cloud is a large, localized, persistent, and often abrupt lowering of cloud that develops beneath the surrounding base of a cumulonimbus cloud and from which tornadoes sometimes form. It is typically beneath the rain-free base (RFB) portion of a thunderstorm, and indicates the area of the strongest updraft within a storm. Rotating wall clouds are an indication of a mesocyclone in a thunderstorm; most strong tornadoes form from these. Many wall clouds do rotate, however some do not.

A hook echo is a pendant or hook-shaped weather radar signature as part of some supercell thunderstorms. It is found in the lower portions of a storm as air and precipitation flow into a mesocyclone resulting in a curved feature of reflectivity. The echo is produced by rain, hail, or even debris being wrapped around the supercell. It is one of the classic hallmarks of tornado-producing supercells. The National Weather Service may consider the presence of a hook echo coinciding with a tornado vortex signature as sufficient to justify issuing a tornado warning.

Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere. Cyclogenesis is an umbrella term for at least three different processes, all of which result in the development of some sort of cyclone, and at any size from the microscale to the synoptic scale.

This is a list of meteorology topics. The terms relate to meteorology, the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting.

A mesoscale convective system (MCS) is a complex of thunderstorms that becomes organized on a scale larger than the individual thunderstorms but smaller than extratropical cyclones, and normally persists for several hours or more. A mesoscale convective system's overall cloud and precipitation pattern may be round or linear in shape, and include weather systems such as tropical cyclones, squall lines, lake-effect snow events, polar lows, and Mesoscale Convective Complexes (MCCs), and generally form near weather fronts. The type that forms during the warm season over land has been noted across North America, Europe, and Asia, with a maximum in activity noted during the late afternoon and evening hours.

An anticyclonic tornado is a tornado which rotates in a clockwise direction in the Northern Hemisphere and a counterclockwise direction in the Southern Hemisphere. The term is a naming convention denoting the anomaly from normal rotation which is cyclonic in upwards of 98 percent of tornadoes. Many anticyclonic tornadoes are smaller and weaker than cyclonic tornadoes, forming from a different process.

A landspout is a term created by atmospheric scientist Howard B. Bluestein in 1985 for a kind of tornado not associated with a mesocyclone. The Glossary of Meteorology defines a landspout as

Tornadogenesis is the process by which a tornado forms. There are many types of tornadoes and these vary in methods of formation. Despite ongoing scientific study and high-profile research projects such as VORTEX, tornadogenesis is a volatile process and the intricacies of many of the mechanisms of tornado formation are still poorly understood.

Convective storm detection is the meteorological observation, and short-term prediction, of deep moist convection (DMC). DMC describes atmospheric conditions producing single or clusters of large vertical extension clouds ranging from cumulus congestus to cumulonimbus, the latter producing thunderstorms associated with lightning and thunder. Those two types of clouds can produce severe weather at the surface and aloft.

A tornado vortex signature or tornadic vortex signature, abbreviated TVS, is a Pulse-Doppler radar weather radar detected rotation algorithm that indicates the likely presence of a strong mesocyclone that is in some stage of tornadogenesis. It may give meteorologists the ability to pinpoint and track the location of tornadic rotation within a larger storm, but it is not an important feature in the National Weather Service's warning operations.

Mesovortices are small scale rotational features found in convective storms, such as those found in bow echos, supercell thunderstorms, and the eyewall of tropical cyclones. They range in size from tens of miles in diameter to a mile or less, and can be immensely intense.

This glossary of meteorology is a list of terms and concepts relevant to meteorology and the atmospheric sciences, their sub-disciplines, and related fields.