Supercell

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Moisture streams in from the side of the precipitation free base and merges into a line of warm uplift region where the tower of the thundercloud is tipped by high altitude shear winds. The high shear causes horizontal vorticity which is tilted within the updraft to become vertical vorticity, and the mass of clouds spins as it gains altitude up to the cap, which can be up to the 55,000 feet (17,000 m)-70,000 feet (21,000 m) above ground for the largest storms, and trailing anvil. The capped, moisture laden air is cooled enough to precipitate as it is rotated toward the cooler region, represented by the turbulent air of the mammatus clouds where the warm air is spilling over top of the cooler, invading air. The cap is formed where shear winds block further uplift for a time, until a relative weakness allows a breakthrough of the cap (an overshooting top); Cooler air to the right in the image may or may not form a shelf cloud, but the precipitation zone will occur where the heat engine of the uplift intermingles with the invading, colder air. As the cooler but drier air circulates into the warm, moisture laden inflow, the cloud base will frequently form a wall, and the cloud base often experiences a lowering, which, in extreme cases, are where tornadoes are formed. Supercell02.svg
Moisture streams in from the side of the precipitation free base and merges into a line of warm uplift region where the tower of the thundercloud is tipped by high altitude shear winds. The high shear causes horizontal vorticity which is tilted within the updraft to become vertical vorticity, and the mass of clouds spins as it gains altitude up to the cap, which can be up to the 55,000 feet (17,000 m)70,000 feet (21,000 m) above ground for the largest storms, and trailing anvil. The capped, moisture laden air is cooled enough to precipitate as it is rotated toward the cooler region, represented by the turbulent air of the mammatus clouds where the warm air is spilling over top of the cooler, invading air. The cap is formed where shear winds block further uplift for a time, until a relative weakness allows a breakthrough of the cap (an overshooting top); Cooler air to the right in the image may or may not form a shelf cloud, but the precipitation zone will occur where the heat engine of the uplift intermingles with the invading, colder air. As the cooler but drier air circulates into the warm, moisture laden inflow, the cloud base will frequently form a wall, and the cloud base often experiences a lowering, which, in extreme cases, are where tornadoes are formed.
A low precipitation supercell shelf cloud. Shelf cloud forms when a cooler air mass under-flows the warmer moisture laden air. Shelfcloud.jpg
A low precipitation supercell shelf cloud. Shelf cloud forms when a cooler air mass under-flows the warmer moisture laden air.
A supercell. While many ordinary thunderstorms (squall line, single-cell, multi-cell) are similar in appearance, supercells are distinguishable by their large-scale rotation. Chaparral Supercell 2.JPG
A supercell. While many ordinary thunderstorms (squall line, single-cell, multi-cell) are similar in appearance, supercells are distinguishable by their large-scale rotation.
Supercells forming near Deshler, Nebraska, United States.
A supercell thunderstorm over Pikes Peak as seen from Palmer Park Supercell over Pikes Peak.jpg
A supercell thunderstorm over Pikes Peak as seen from Palmer Park

A supercell is a thunderstorm characterized by the presence of a mesocyclone: a deep, persistently rotating updraft. [1] For this reason, these storms are sometimes referred to as rotating thunderstorms. [2] Of the four classifications of thunderstorms (supercell, squall line, multi-cell, and single-cell), 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.

Thunderstorm type of weather

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.

Mesocyclone

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.

Vertical draft small‐scale current of rising air

An updraft is a small‐scale current of rising air, often within a cloud.

Contents

Supercells are often put into three classification types: Classic, Low-precipitation (LP), and High-precipitation (HP). LP supercells are usually found in climates that are more arid, such as the high plains of the United States, and HP supercells are most often found in moist climates. Supercells can occur anywhere in the world under the right pre-existing weather conditions, but they are most common in the Great Plains of the United States in an area known as Tornado Alley and in the Tornado Corridor of Argentina, Uruguay and southern Brazil.

Great Plains broad expanse of flat land west of the Mississippi River and east of the Rocky Mountains in the United States and Canada

The Great Plains is the broad expanse of flat land, much of it covered in prairie, steppe, and grassland, that lies west of the Mississippi River tallgrass prairie in the United States and east of the Rocky Mountains in the U.S. and Canada. It embraces:

Tornado Alley Area in the U.S. with frequent tornado outbreaks

Tornado Alley is a colloquial term for the area of the United States where tornadoes are most frequent.

Argentina federal republic in South America

Argentina, officially the Argentine Republic, is a country located mostly in the southern half of South America. Sharing the bulk of the Southern Cone with Chile to the west, the country is also bordered by Bolivia and Paraguay to the north, Brazil to the northeast, Uruguay and the South Atlantic Ocean to the east, and the Drake Passage to the south. With a mainland area of 2,780,400 km2 (1,073,500 sq mi), Argentina is the eighth-largest country in the world, the fourth largest in the Americas, and the largest Spanish-speaking nation. The sovereign state is subdivided into twenty-three provinces and one autonomous city, Buenos Aires, which is the federal capital of the nation as decided by Congress. The provinces and the capital have their own constitutions, but exist under a federal system. Argentina claims sovereignty over part of Antarctica, the Falkland Islands, and South Georgia and the South Sandwich Islands.

Characteristics

Supercells are usually found isolated from other thunderstorms, although they can sometimes be embedded in a squall line. Typically, supercells are found in the warm sector of a low pressure system propagating generally in a north easterly direction in line with the cold front of the low pressure system. Because they can last for hours, they are known as quasi-steady-state storms. Supercells have the capability to deviate from the mean wind. If they track to the right or left of the mean wind (relative to the vertical wind shear), they are said to be "right-movers" or "left-movers," respectively. Supercells can sometimes develop two separate updrafts with opposing rotations, which splits the storm into two supercells: one left-mover and one right-mover.

Squall line

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.

Wind shear

Wind shear, sometimes referred to as wind gradient, is a difference in wind speed or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical or horizontal wind shear. Vertical wind shear is a change in wind speed or direction with change in altitude. Horizontal wind shear is a change in wind speed with change in lateral position for a given altitude.

Supercells can be any size – large or small, low or high topped. They usually produce copious amounts of hail, torrential rainfall, strong winds, and substantial downbursts. Supercells are one of the few types of clouds that typically spawn tornadoes within the mesocyclone, although only 30% or fewer do so. [3]

Hail Form of solid precipitation

Hail is a form of solid precipitation. It is distinct from ice pellets, though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets fall generally in cold weather while hail growth is greatly inhibited during cold surface temperatures.

Rain liquid water in the form of droplets that have condensed from atmospheric water vapor and then precipitated

Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then become heavy enough to fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides suitable conditions for many types of ecosystems, as well as water for hydroelectric power plants and crop irrigation.

Downburst

A downburst is a strong ground-level wind system that emanates from a point source above and blows radially, that is, in straight lines in all directions from the point of contact at ground level. Often producing damaging winds, it may be confused with a tornado, where high-velocity winds circle a central area, and air moves inward and upward; by contrast, in a downburst, winds are directed downward and then outward from the surface landing point.

Geography

Supercells can occur anywhere in the world under the right weather conditions. The first storm to be identified as the supercell type was the Wokingham storm over England, which was studied by Keith Browning and Frank Ludlam in 1962. [4] Browning did the initial work that was followed up by Lemon and Doswell to develop the modern conceptual model of the supercell. [5] To the extent that records are available, supercells are most frequent in the Great Plains of the central United States and southern Canada extending into the southeastern U.S. and northern Mexico; east-central Argentina and adjacent regions of Uruguay; Bangladesh and parts of eastern India; South Africa; and eastern Australia. [6] Supercells occur occasionally in many other mid-latitude regions, including Eastern China and throughout Europe. The areas with highest frequencies of supercells are similar to those with the most occurrences of tornadoes; see tornado climatology and Tornado Alley.

Wokingham market town and civil parish in Berkshire in South East England

Wokingham is a historic market town in Berkshire, England, 39 miles (63 km) west of London, 7 miles (11 km) southeast of Reading, 8 miles (13 km) north of Camberley and 4 miles (6 km) west of Bracknell. At the 2011 census, it had a population of 30,690.

England Country in north-west Europe, part of the United Kingdom

England is a country that is part of the United Kingdom. It shares land borders with Wales to the west and Scotland to the north-northwest. The Irish Sea lies west of England and the Celtic Sea lies to the southwest. England is separated from continental Europe by the North Sea to the east and the English Channel to the south. The country covers five-eighths of the island of Great Britain, which lies in the North Atlantic, and includes over 100 smaller islands, such as the Isles of Scilly and the Isle of Wight.

Keith Anthony Browning is a British meteorologist who worked at Imperial College London, the Met Office, and the University of Reading departments of meteorology. His work with Frank Ludlam on the supercell thunderstorm at Wokingham, UK in 1962 was the first detailed study of such a storm. His well regarded research covered many areas of mesoscale meteorology including developing the theory of the sting jet. Arguably his greatest talent is his intuitive understanding of complex three-dimensional meteorological processes which he has described more simply using conceptual models.

Anatomy of a supercell

The current conceptual model of a supercell was described in Severe Thunderstorm Evolution and Mesocyclone Structure as Related to Tornadogenesis by Leslie R. Lemon and Charles A. Doswell III. (See Lemon technique).

Lemon technique

The Lemon technique is a method used by meteorologists using weather radar to determine the relative strength of thunderstorm cells in a vertically sheared environment. It is named for Leslie R. Lemon, the co-creator of the current conceptual model of a supercell. The Lemon technique is largely a continuation of work by Keith A. Browning, who first identified and named the supercell.

Supercells derive their rotation through tilting of horizontal vorticity (an invisible horizontal vortex) caused by wind shear. Strong updrafts lift the air turning about a horizontal axis and cause this air to turn about a vertical axis. This forms the deep rotating updraft, the mesocyclone.

A cap or capping inversion is usually required to form an updraft of sufficient strength. The cap puts an inverted (warm-above-cold) layer above a normal (cold-above-warm) boundary layer, and by preventing warm surface air from rising, allows one or both of the following:

This creates a warmer, moister layer below a cooler layer, which is increasingly unstable (because warm air is less dense and tends to rise). When the cap weakens or moves, explosive development follows.

In North America, supercells usually show up on Doppler radar as starting at a point or hook shape on the southwestern side, fanning out to the northeast. The heaviest precipitation is usually on the southwest side, ending abruptly short of the rain-free updraft base or main updraft (not visible to radar). The rear flank downdraft , or RFD, carries precipitation counterclockwise around the north and northwest side of the updraft base, producing a "hook echo" that indicates the presence of a mesocyclone.

Wind shear (red) sets air spinning (green) Meso-1.svg
Wind shear (red) sets air spinning (green)
The updraft (blue) 'bends' the spinning air upwards Meso-2.svg
The updraft (blue) 'bends' the spinning air upwards
The updraft starts rotating with the spinning column of air Meso-3.svg
The updraft starts rotating with the spinning column of air

Structure of a supercell

Structure of a supercell. Northwestward view in the Northern Hemisphere Supercell.svg
Structure of a supercell. Northwestward view in the Northern Hemisphere
Diagram of supercell from above. RFD: rear flank downdraft, FFD: front flank downdraft, V: V-notch, U: Main Updraft, I: Updraft/Downdraft Interface, H: hook echo Supercell-above.svg
Diagram of supercell from above. RFD: rear flank downdraft, FFD: front flank downdraft, V: V-notch, U: Main Updraft, I: Updraft/Downdraft Interface, H: hook echo

Overshooting top

This "dome" feature appears above the strongest updraft location on the anvil of the storm. It is a result of a very powerful updraft; enough to break through the upper levels of the troposphere. An observer who is at ground level too close to the storm is unable to see the overshooting top due to the fact that the anvil blocks the sight of this feature. The overshooting is visible from satellite images as a "bubbling" amidst the otherwise smooth upper surface of the anvil cloud.

Anvil

An anvil forms when the storm's updraft collides with the upper levels of the lowest layer of the atmosphere, or the tropopause, and has nowhere else to go due to the laws of fluid dynamics- specifically pressure, humidity, and density. The anvil is very cold and virtually precipitation free even though virga can be seen falling from the forward sheared anvil. Since there is so little moisture in the anvil, winds can move freely. The clouds take on their anvil shape when the rising air reaches 15,200–21,300 metres (50,000–70,000 ft) or more. The anvil's distinguishing feature is that it juts out in front of the storm like a shelf. In some cases, it can even shear backwards, called a backsheared anvil, another sign of a very strong updraft.

Precipitation-free base

This area, typically on the southern side of the storm in North America, is relatively precipitation free. This is located beneath the main updraft, and is the main area of inflow. While no precipitation may be visible to an observer, large hail may be falling from this area. A region of this area is called the Vault. It is more accurately called the main updraft area.

Wall cloud

The wall cloud forms near the downdraft/updraft interface. This "interface" is the area between the precipitation area and the precipitation-free base. Wall clouds form when rain-cooled air from the downdraft is pulled into the updraft. This wet, cold air quickly saturates as it is lifted by the updraft, forming a cloud that seems to "descend" from the precipitation-free base. Wall clouds are common and are not exclusive to supercells; only a small percentage actually produce a tornado, but if a storm does produce a tornado it usually exhibits wall clouds that persist for more than ten minutes. Wall clouds that seem to move violently up or down, and violent movements of cloud fragments (scud or fractus) near the wall cloud are indications that a tornado could form.

Mammatus clouds

Mammatus (Mamma, Mammatocumulus) are bulbous or pillow-like cloud formations extending from beneath the anvil of a thunderstorm. These clouds form as cold air in the anvil region of a storm sinks into warmer air beneath it. Mammatus are most apparent when they are lit from one side or below and are therefore at their most impressive near sunset or shortly after sunrise when the sun is low in the sky. Mammatus are not exclusive to supercells and can be associated with developed thunderstorms and cumulonimbus.

Forward Flank Downdraft (FFD)

This is generally the area of heaviest and most widespread precipitation. For most supercells, the precipitation core is bounded on its leading edge by a shelf cloud that results from rain-cooled air within the precipitation core spreading outward and interacting with warmer, moist air from outside of the cell. Between the precipitation-free base and the FFD, a "vaulted" or "cathedral" feature can be observed. In high precipitation supercells an area of heavy precipitation may occur beneath the main updraft area where the vault would alternately be observed with classic supercells.

Rear Flank Downdraft (RFD)

The RFD of a supercell is a very complex and not yet fully understood feature. RFD mainly occur within classic and HP supercells although RFDs have been observed within LP supercells. The RFD of a supercell is believed to play a large part in tornadogenesis by further tightening rotation within the surface mesocyclone. RFDs are caused by mid level steering winds of a supercell colliding with the updraft tower and moving around it in all directions; specifically the flow that is redirected downward is referred to as the RFD. This downward surge of relatively cool mid level air, due to interactions between dew points, humidity, and condensation of the converging of air masses, can reach very high speeds and is known to cause widespread wind damage. The radar signature of an RFD is a hook like structure where sinking air has brought with it precipitation.

Vault

A vault is not observed with all supercells. The vault can only be identified visibly due to it visibly appearing to be free of precipitation but usually containing large hail. On Doppler radar, the region of very high precipitation echos with a very sharp gradient perpendicular to the RFD.

Flanking line

A flanking line is a line of smaller cumulonimbi or cumulus that form in the warm rising air pulled in by the main updraft. Due to convergence and lifting along this line, landspouts sometimes occur on the outflow boundary of this region.

Radar features of a supercell

Radar reflectivity map Supercell in Wichita Falls.svg
Radar reflectivity map

The "hook echo" is the area of confluence between the main updraft and the rear flank downdraft (RFD). This indicates the position of the mesocyclone, and probably a tornado.

This is a region of low radar reflectivity bounded above by an area of higher radar reflectivity with an untilted updraft. This is evidence of a strong updraft, and oftentimes the presence of a tornado.

A "notch" of weak reflectivity on the inflow side of the cell. This is not a V-Notch.

A "V" shaped notch on the leading edge of the cell, opening away from the main downdraft. This is an indication of divergent flow around a powerful updraft.

This three body scatter spike is a region of weak echoes found radially behind the main reflectivity core at higher elevations when large hail is present. [7]

Supercell variations

Supercell thunderstorms are sometimes classified by meteorologists and storm spotters into three categories. However, not all supercells fit neatly into any one category, being hybrid storms, and many supercells may fall into different categories during different periods of their lifetimes. The standard definition given above is referred to as the Classic supercell. All types of supercells typically produce severe weather.

Low Precipitation (LP)

Schematics of an LP supercell Low precipitation supercell thunderstorm.gif
Schematics of an LP supercell
Idealized view of an LP supercell Lp supercell.jpg
Idealized view of an LP supercell

LP supercells contain a small and relatively light precipitation (rain/hail) core that is well separated from the updraft. The updraft is intense and LPs are inflow dominant storms. The updraft tower is typically more strongly tilted and the deviant rightward motion lesser than for other supercell types. The forward flank downdraft (FFD) is noticeably weaker than for other supercell types and the rear-flank downdraft (RFD) is much weaker—even visually absent in many cases. Like classic supercells, LP supercells tend to form within stronger mid-to-upper level storm-relative wind shear, [8] however, the atmospheric environment leading to their formation is not well understood. The moisture profile of the atmosphere, particularly the depth of the elevated dry layer, also appears to be important [9] and the low-to-mid level shear may also be important. [10]

This type of supercell may be easily identifiable with "sculpted" cloud striations in the updraft base or even a "corkscrewed" or "barber pole" appearance on the updraft, and sometimes an almost "anorexic" look compared to classic supercells. This is because they often form within drier moisture profiles (often initiated by dry lines) leaving LPs with little available moisture despite high mid-to-upper level environmental winds. They most often dissipate rather than turning into classic or HP supercells, although it is still not unusual for LPs to do the latter, especially when moving into a much moister air mass. LPs were first formally described by Howard Bluestein in the early 1980s [11] although storm chasing scientists noticed them throughout the 1970s. [12] Classic supercells may wither yet maintain updraft rotation as they decay, becoming more like the LP type in a process known as "downscale transition" that also applies to LP storms and this process is thought to be how many LPs dissipate. [13]

LP supercells rarely spawn tornadoes and those that form tend to be weak, small, and high based tornadoes but strong tornadoes have been observed. These storms although generating lesser precipitation amounts and producing smaller precipitation cores can generate huge hail. LPs may produce hail larger than baseballs in clear air where no rainfall is visible. [14] LPs are thus hazardous to people and animals caught outside as well as to storm chasers and spotters. Due to the lack of a heavy precipitation core, LP supercells often exhibit relatively weak radar reflectivity without clear evidence of a hook echo, when in fact they are producing a tornado at the time. LP supercells may not even be recognized as supercells in reflectivity data unless one is trained or experienced on their radar characteristics. [15] This is where observations by storm spotter and storm chasers may be of vital importance in addition to Doppler velocity (and polarimetric) radar data. High-based shear funnel clouds sometimes form midway between the base and the top of the storm, descending from the main Cb (cumulonimbus) cloud.[ citation needed ] Lightning discharges may be less frequent compared to other supercell types, but on occasion LPs are prolific sparkers, and the discharges are more likely to occur as intracloud lightning rather than cloud-to-ground lightning.[ citation needed ]

In North America, these storms most prominently form in the semi-arid Great Plains during the spring and summer months. Moving east and southeast, they often collide with moist air masses from the Gulf of Mexico, leading to the formation of HP supercells in areas just to the west of Interstate 35 before dissipating (or coalescing into squall lines) at variable distances farther east. LP supercells have been observed as far east as Illinois and Indiana, [16] however. LP supercells can occur as far north as Montana, North Dakota, and even in the Prairie Provinces of Alberta, Saskatchewan, and Manitoba in Canada. They have also been observed by storm chasers in Australia and Argentina (the Pampas).[ citation needed ]

LP supercells are quite sought after by storm chasers, because the limited amount of precipitation makes sighting tornadoes at a safe distance much less difficult than with a classic or HP supercell and more so because of the unobscured storm structure unveiled. During spring and early summer, areas in which LP supercells are readily spotted include southwestern Oklahoma and northwestern Texas, among other parts of the western Great Plains.[ citation needed ]

High Precipitation (HP)

Schematics of an HP supercell High precipitation supercell thunderstorm.gif
Schematics of an HP supercell
High precipitation supercell HPsupercell.jpg
High precipitation supercell

The HP supercell has a much heavier precipitation core that can wrap all the way around the mesocyclone. These are especially dangerous storms, since the mesocyclone is wrapped with rain and can hide a tornado (if present) from view. These storms also cause flooding due to heavy rain, damaging downbursts and weak tornadoes, although they are also known to produce strong to violent tornadoes. They have a lower potential for damaging hail than Classic and LP supercells, although damaging hail is possible. It has been observed by some spotters that they tend to produce more cloud-to-ground and intracloud lightning than the other types. Also, unlike the LP and Classic types, severe events usually occur at the front (southeast) of the storm. The HP supercell is the most common type of supercell in the United States east of Interstate 35, in the southern parts of the provinces of Ontario and Quebec in Canada, and in the central portions of Argentina and Uruguay.

Mini-supercell or low-topped supercell

Whereas classic, HP, and LP refer to different precipitation regimes and mesoscale frontal structures, another variation was identified in the early 1990s by Jon Davies. [17] These smaller storms were initially called mini-supercells [18] but are now commonly referred to as low-topped supercells. These are also subdivided into Classic, HP and LP types.

Effects

Satellite view of a supercell Supercell04.jpg
Satellite view of a supercell

Supercells can produce 2 inch hail, winds over 70 mph, EF3 or EF4 or EF5 tornadoes, flooding, frequent to continuous lightning, and very heavy rain.

Severe events associated with a supercell almost always occur in the area of the updraft/downdraft interface. In the Northern Hemisphere, this is most often the rear flank (southwest side) of the precipitation area in LP and classic supercells, but sometimes the leading edge (southeast side) of HP supercells.

Examples worldwide

Asia

Some reports suggest that the deluge on 26 July 2005 in Mumbai, India was caused by a supercell when there was a cloud formation 15 kilometres (9.3 mi) high over the city. On this day 944 mm (37.2 in) of rain fell over the city, of which 700 mm (28 in) fell in just four hours. The rainfall coincided with a high tide, which exacerbated conditions. [19] [ not in citation given ]

Supercells occur commonly from March–May in Bangladesh, West Bengal and the bordering north-eastern Indian states including Tripura. Supercells that produce very high winds with hail and occasional tornadoes are observed in these regions, with them also occurring along the Northern Plains of India and Pakistan. On March 23, 2013, a massive tornado ripped through Brahmanbaria district in Bangladesh, killing 20 and injuring 200. [20]

Australia

On April 14, 1999, a severe storm later classified as a supercell hit the east coast of New South Wales. It is estimated that the storm dropped 500,000 tonnes (490,000 long tons; 550,000 short tons) worth of hailstones during its course. At the time it was the most costly disaster in Australia's insurance history, causing an approximated A$2.3 billion worth of damage, of which A$1.7 billion was covered by insurance.

On February 27, 2007, a supercell hit Canberra, dumping nearly thirty-nine centimetres (15 inches) of ice in Civic. The ice was so heavy that a newly built shopping center's roof collapsed, birds were killed in the hail produced from the supercell, and people were stranded. The following day many homes in Canberra were subjected to flash flooding, caused either by storm water infrastructure's inability to cope or through mud slides from cleared land. [21]

On 6 March 2010, supercell storms hit Melbourne. The storms caused flash flooding in the center of the city and tennis ball-sized (10 cm or 4 in) hailstones hit cars and buildings, causing more than $220 million worth of damage, and sparking 40,000-plus insurance claims. In just 18 minutes, 19 cm (7.5 in) of rain fell, causing havoc as streets were flooded and trains, planes and cars were brought to a standstill. [22]

That same month, on March 22, 2010 a supercell hit Perth. This storm was one of the worst in the city's history, causing hail stones of 6 centimetres (2.4 in) in size and torrential rain. The city had its average March rainfall in just seven minutes during the storm. Hail stones caused severe property damage, from dented cars to smashed windows. [23] The storm itself caused more than 100 million dollars in damage. [24]

On November 27, 2014 a supercell hit the inner city suburbs including the CBD of Brisbane. Hailstones up to softball size cut power to 71,000 properties, injuring 39 people, [25] and causing a damage bill of $1 billion AUD. [26] A wind gust of 141 km/h was recorded at Archerfield Airport [27]

South America

An area in South America known as the Tornado Corridor is considered to be the second most frequent location for severe weather, after Tornado Alley in the United States.[ citation needed ] The region, which covers portions of Argentina, Uruguay, Paraguay, and Brazil during the spring and summer, often experiences strong thunderstorms, which may include tornadoes. One of the first known South American supercell thunderstorms to include tornadoes occurred on September 16, 1816 and destroyed the town of Rojas (240 kilometres (150 mi) west of the city of Buenos Aires).[ citation needed ]

On September 20, 1926, an EF4 tornado struck the city of Encarnación (Paraguay), killing over 300 people and making it the second deadliest tornado in South America. On 21 April 1970, the town of Fray Marcos in the Department of Florida, Uruguay experienced an F4 tornado that killed 11, the strongest in the history of the nation. January 10, 1973 saw the most severe tornado in the history of South America: The San Justo tornado, 105 km north of the city of Santa Fe (Argentina), was rated EF5, making it the strongest tornado ever recorded in the southern hemisphere, with winds exceeding 400 km/h. On April 13, 1993, in less than 24 hours in the province of Buenos Aires was given the largest tornado outbreak in the history of South America. There were more than 300 tornadoes recorded, with intensities between F1 and F3. The most affected towns were Henderson (EF3), Urdampilleta (EF3) and Mar del Plata (EF2). In December 2000, a series of twelve tornadoes (only registered) affected the Greater Buenos Aires and the province of Buenos Aires, causing serious damage. One of them struck the town of Guernica, and, just two weeks later, in January 2001, an EF3 again devastated Guernica, killing 2 people.

The December 26, 2003 Tornado F3 happened in Cordoba, with winds exceeding 300 km/h, which hit Córdoba Capital, hit just 6 km from the city center, in the area known as CPC Route 20, especially neighborhoods of San Roque and Villa Fabric, killing 5 people and injuring hundreds. The tornado that hit the State of São Paulo in 2004 was one of the most destructive in the state. Destroyed several industrial buildings, with 400 houses, left 1 dead and 11 wounded. The tornado was rated EF3, but many claim it was a tornado EF4. In November 2009, four tornadoes category F1 and F2 reached the town of Posadas (capital of the province of Misiones, Argentina), generating serious damage in the city. Three of the tornado affected area of the airport, causing damage in Barrio Belén. On April 4, 2012, the Gran Buenos Aires was hit by the storm Buenos Aires, with intensities F1 and F2, which left nearly 30 dead in various locations.

On February 21, 2014, in Berazategui (province of Buenos Aires), a tornado of intensity F1 caused material damage including a car was, with two occupants inside, which was elevated a few feet off the ground and flipped over asphalt, both the driver and his passenger were slightly injured. The tornado caused no fatalities. The severe weather that occurred on Tuesday 8/11 had features rarely seen in such magnitude in Argentina. In many towns of La Pampa, San Luis, Buenos Aires and Cordoba, intense hail stones fell up to 6 cm in diameter. On Sunday December 8, 2013, severe storms took place in the center and the coast. The most affected province was Córdoba, storms and supercells type "bow echos" also developed in Santa Fe and San Luis.

Europe

In 2009, on the night of Monday May 25, a supercell formed over Belgium. It was described by Belgian meteorologist Frank Deboosere as "one of the worst storms in recent years" and caused much damage in Belgium - mainly in the provinces of East Flanders (around Ghent), Flemish Brabant (around Brussels) and Antwerp. The storm occurred between about 1:00am and 4:00am local time. An incredible 30,000 lightning flashes were recorded in 2 hours - including 10,000 cloud-to-ground strikes. Hailstones up to 6 centimetres (2.4 in) across were observed in some places and wind gusts over 90 km/h (56 mph); in Melle near Ghent a gust of 101 km/h (63 mph) was reported. Trees were uprooted and blown onto several motorways. In Lillo (east of Antwerp) a loaded goods train was blown from the rail tracks. [28] [29]

On August 18, 2011, the rock festival Pukkelpop in Kiewit, Hasselt (Belgium) may have been seized by a supercell with mesocyclone around 18:15. Tornado-like winds were reported, trees of over 30 centimetres (12 in) diameter were felled and tents came down. Severe hail scourged the campus. Five people reportedly died and over 140 people were injured. One more died a week later. The event was suspended. Buses and trains were mobilised to bring people home.

On June 28, 2012, three supercells affected England. Two of them formed over the Midlands, producing hailstones reported to be larger than golfballs, with conglomerate stones up to 10 cm across. Burbage in Leicestershire saw some of the most severe hail. Another supercell produced a tornado near Sleaford, in Lincolnshire.

A third supercell affected the North East region of England. The storm struck the Tyneside area directly and without warning during evening rush hour causing widespread damage and travel chaos, with people abandoning cars and being trapped due to lack of public transport. Flooded shopping malls were evacuated, Newcastle station was shut, as was the Tyne & Wear Metro, and main road routes were flooded leading to massive tailbacks. 999 land line services were knocked out in some areas and the damage ran to huge amounts only visible the next day after water cleared. Many parts of County Durham and Northumberland were also affected, with thousands of homes across the North East left without power due to lightning strikes. Lightning was seen to hit the Tyne Bridge (Newcastle).

In Europe, the mini-supercell, or low-topped supercell, is very common, especially when showers and thunderstorms develop in cooler polar air masses with a strong jet stream above, especially in the left exit-region of a jetstreak.

North America

The Tornado Alley is a region of the central United States where severe weather is common, particularly tornadoes. Supercell thunderstorms can affect this region at any time of the year, but they are most common in the spring. Tornado watches and warnings are frequently necessary in the spring and summer. Most places from the Great Plains to the East Coast of the United States and north as far as the Canadian Prairies, the Great Lakes region, and the St. Lawrence River will experience one or more supercells each year.[ citation needed ]

Gainesville, Georgia was the site of the fifth deadliest tornado in U.S. history in 1936, where Gainesville was devastated and 203 people were killed. [30]

The 1980 Grand Island tornado outbreak affected the city of Grand Island, Nebraska on June 3, 1980. Seven tornadoes touched down in or near the city that night, killing 5 and injuring 200. [31]

The Elie, Manitoba tornado was an F5 that struck the town of Elie, Manitoba on June 22, 2007. While several houses were leveled, no one was injured or killed by the tornado. [32] [33] [34]

A massive tornado outbreak on May 3, 1999 spawned an F5 tornado in the area of Oklahoma City that had the highest recorded winds on Earth. [35] This outbreak spawned over 66 tornadoes in Oklahoma alone. On this day throughout the area of Oklahoma, Kansas and Texas, over 141 tornadoes were produced. This outbreak resulted in 50 fatalities and 895 injuries.[ citation needed ]

A series of tornadoes, which occurred in May 2013, caused severe devastation to Oklahoma City in general. The first tornado outbreaks occurred on May 18 to May 21 when a series of tornadoes hit. From one of the storms developed a tornado which was later rated EF5, which traveled across parts of the Oklahoma City area, causing a severe amount of disruption. This tornado was first spotted in Newcastle. It touched the ground for 39 minutes, crossing through a heavily populated section of Moore.[ citation needed ] Winds with this tornado peaked at 210 miles per hour (340 km/h). [36] Twenty-three fatalities and 377 injuries were caused by the tornado. [37] [38] Sixty-one other tornadoes were confirmed during the storm period. Later on in the same month, on the night of May 31, 2013, another eight deaths were confirmed from what became the widest tornado on record which hit El Reno, Oklahoma, one of a series of tornadoes and funnel clouds which hit nearby areas. [39]

South Africa

South Africa witnesses several supercell thunderstorms each year with the inclusion of isolated tornadoes. On most occasions these tornadoes occur in open farmlands and rarely cause damage to property, as such many of the tornadoes which do occur in South Africa are not reported. The majority of supercells develop in the central, northern, and north eastern parts of the country. The Free State, Gauteng, and Kwazulu Natal are typically the provinces where these storms are most commonly experienced, though supercell activity is not limited to these provinces. On occasion, hail reaches sizes in excess of golf balls, and tornadoes, though rare, also occur.

On 6 May 2009, a well-defined hook echo was noticed on local South African radars, along with satellite imagery this supported the presence of a strong supercell storm. Reports from the area indicated heavy rains, winds and large hail. [40]

On October 2, 2011, two devastating tornadoes tore through two separate parts of South Africa on the same day, hours apart from each other. The first, classified as an EF2 hit Meqheleng, the informal settlement outside Ficksburg, Free State which devastated shacks and homes, uprooted trees, and killed one small child. The second, which hit the informal settlement of Duduza, Nigel in the Gauteng province, also classified as EF2 hit hours apart from the one that struck Ficksburg. This tornado completely devastated parts of the informal settlement and killed two children, destroying shacks and RDP homes. [41] [42]

See also

Related Research Articles

Wall cloud cloud formation

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.

Hook echo

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.

Gustnado short-lived, shallow surface-based vortex generated by a thunderstorm

A gustnado is a short-lived, shallow surface-based vortex which forms within the downburst emanating from a thunderstorm. The name is a portmanteau by elision of "gust front tornado", as gustnadoes form due to non-tornadic straight-line wind features in the downdraft (outflow), specifically within the gust front of strong thunderstorms. Gustnadoes tend to be noticed when the vortices loft sufficient debris or form condensation cloud to be visible although it is the wind that makes the gustnado, similarly to tornadoes. As these eddies very rarely connect from the surface to the cloud base, they are very rarely considered as tornadoes. The gustnado has little in common with tornadoes structurally or dynamically in regard to vertical development, intensity, longevity, or formative process --as classic tornadoes are associated with mesocyclones within the inflow (updraft) of the storm, not the outflow.

Anticyclonic tornado

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, as either companion/satellite tornadoes or nonmesocyclonic tornadoes.

Landspout slang term for a kind of tornado not associated with the mesocyclone of a thunderstorm

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

Cumulonimbus incus variety of cloud

A cumulonimbus incus also known as an anvil cloud is a cumulonimbus cloud which has reached the level of stratospheric stability and has formed the characteristic flat, anvil-top shape. It signifies the thunderstorm in its mature stage, succeeding the cumulonimbus calvus stage. Cumulonimbus incus is a sub-form of Cumulonimbus capillatus.

Tornadogenesis process by which a tornado forms

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.

Rear flank downdraft

The rear flank downdraft or RFD is a region of dry air wrapping around the back of a mesocyclone in a supercell thunderstorm. These areas of descending air are thought to be essential in the production of many supercellular tornadoes. Large hail within the rear flank downdraft often shows up brightly as a hook on weather radar images, producing the characteristic hook echo, which often indicates the presence of a tornado.

Overshooting top part of the anvil of a thunderstorm

An overshooting top is a dome-like protrusion shooting out of the top of the anvil of a thunderstorm. When an overshooting top is present for 10 minutes or longer, it's a strong indication the storm is severe.

Multicellular thunderstorm

A multicellular thunderstorm cluster is a thunderstorm that is composed of multiple cells, each being at a different stage in the life cycle of a thunderstorm. It appears as several anvils clustered together. A cell is an updraft/downdraft couplet. These different cells will dissipate as new cells form and continue the life of the multicellular thunderstorm cluster with each cell taking a turn as the dominant cell in the group.

Air-mass thunderstorm

An air-mass thunderstorm, also called an "ordinary", "single cell", or "garden variety" thunderstorm, is a thunderstorm that is generally weak and usually not severe. These storms form in environments where at least some amount of Convective Available Potential Energy (CAPE) is present, but very low levels of wind shear and helicity. The lifting source, which is a crucial factor in thunderstorm development, is usually the result of uneven heating of the surface, though they can be induced by weather fronts and other low-level boundaries associated with wind convergence. The energy needed for these storms to form comes in the form of insolation, or solar radiation. Air-mass thunderstorms do not move quickly, last no longer than an hour, and have the threats of lightning, as well as showery light, moderate, or heavy rainfall. Heavy rainfall can interfere with microwave transmissions within the atmosphere.

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.

Vertically integrated liquid

Vertically integrated liquid (VIL) is an estimate of the total mass of precipitation in the clouds. The measurement is obtained by observing the reflectivity of the air which is obtained with weather radar.

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

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