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Tornado A tornado is a violently 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. It is often referred to as a twister, whirlwind or cyclone, altho ...
es have been recorded on all continents except Antarctica. They are most common in the middle latitudes where conditions are often favorable for convective storm development. The United States has the most tornadoes of any country, as well as the strongest and most violent tornadoes. A large portion of these tornadoes form in an area of the central United States popularly known as
Tornado Alley Tornado Alley is a loosely defined area of the central United States where tornadoes are most frequent. The term was first used in 1952 as the title of a research project to study severe weather in areas of Texas, Louisiana, Oklahoma, Kansas, S ...
. Canada experiences the second most tornadoes.
Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...
and the
prairie provinces The Canadian Prairies (usually referred to as simply the Prairies in Canada) is a region in Western Canada. It includes the Canadian portion of the Great Plains and the Prairie Provinces, namely Alberta, Saskatchewan, and Manitoba. These pr ...
see the highest frequency. Other areas of the world that have frequent tornadoes include significant portions of Europe, South Africa, Philippines, Bangladesh, parts of Argentina, Uruguay, and southern and southeastern Brazil, northern Mexico, New Zealand, and far eastern Asia. Tornado reports in the U.S. have been officially collated since 1950. These reports have been gathered by the
National Climatic Data Center The United States National Climatic Data Center (NCDC), previously known as the National Weather Records Center (NWRC), in Asheville, North Carolina, was the world's largest active archive of weather data. Starting as a tabulation unit in New ...
(NCDC), based in Asheville, North Carolina. A tornado can be reported more than once, such as when a storm crosses a county line and reports are made from two counties. The severity of tornadoes is measured by the
Enhanced Fujita Scale The Enhanced Fujita scale (abbreviated as EF-Scale) rates tornado intensity based on the severity of the damage they cause. It is used in some countries, including the United States, Canada, China, and Mongolia. The Enhanced Fujita scale repla ...
, which measures
tornado intensity Tornado intensity can be measured by ''in situ'' or remote sensing measurements, but since these are impractical for wide-scale use, intensity is usually inferred by proxies, such as damage. The Fujita scale, Enhanced Fujita scale, and the In ...
on a scale of EF0 to EF5 based on wind speed and intensity of destruction. The ratings are made after the tornado has dissipated and the damage trail is carefully studied by weather professionals. A series of continuous tornado outbreaks is known as a
tornado outbreak sequence A tornado outbreak sequence, or tornado outbreak day sequence, sometimes referred to as an extended tornado outbreak, is a period of continuous or nearly continuous high tornado activity consisting of a series of tornado outbreaks over multiple days ...
.


Necessary conditions

Not every
thunderstorm 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 somet ...
,
supercell A supercell is a thunderstorm characterized by the presence of a mesocyclone: a deep, persistently rotating updraft. Due to this, these storms are sometimes referred to as rotating thunderstorms. Of the four classifications of thunderstorms ( ...
,
squall line A squall line, or more accurately a quasi-linear convective system (QLCS), is a line of thunderstorms, often forming along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front (which often are accomp ...
, or
tropical cyclone A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Dep ...
will produce a tornado. Precisely the right atmospheric conditions are required for the formation of even a weak tornado. Tornadoes can form in any month when conditions are favorable. 1,000 or more tornadoes a year are reported in the contiguous United States. The high frequency of tornadoes in North America is largely due to geography, as moisture from the Gulf of Mexico is easily advected into the midcontinent with few topographic barriers in the way. The
Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico ...
block Pacific-sourced moisture and buckle the atmospheric flow, forcing the drier air to mid-levels of the
troposphere The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From ...
. Downsloping winds off the Rockies force the formation of a
dry line A dry line (also called a dew point line, or Marfa front, after Marfa, Texas) is a line across a continent that separates moist air and dry air. One of the most prominent examples of such a separation occurs in central North America, especially ...
when the flow aloft is strong, while the
Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United St ...
fuels abundant low-level moisture. This unique topography allows for frequent collisions of warm and cold air, the conditions that breed strong, long-lived storms throughout the year. This area extends into Canada, particularly
Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...
and the
Prairie Provinces The Canadian Prairies (usually referred to as simply the Prairies in Canada) is a region in Western Canada. It includes the Canadian portion of the Great Plains and the Prairie Provinces, namely Alberta, Saskatchewan, and Manitoba. These pr ...
. Tornadoes can also be triggered by hurricanes, although the tornadoes caused by hurricanes are often much weaker and harder to spot. Winter is the least common time for tornadoes to occur, since hurricane activity is virtually non-existent at this time, and it is more difficult for warm, moist maritime tropical air to take over the frigid Arctic air from Canada. Winter tornado occurrences are found mostly in the Gulf states and
Florida Florida is a U.S. state, state located in the Southeastern United States, Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia (U.S. state), Geo ...
during winter (although there have been some notable exceptions). South America's tornado corridor region is favorable for tornadoes and severe thunderstorms, due to the large size of the Pampas Plain where the cold, dry air from Patagonia, the
Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S l ...
, and Antarctica collides with warm, moist air from areas of Brazil, northern Argentina, and Paraguay. Europe has some small "tornado alleys"—probably because of
frontal Front may refer to: Arts, entertainment, and media Films * ''The Front'' (1943 film), a 1943 Soviet drama film * ''The Front'', 1976 film Music *The Front (band), an American rock band signed to Columbia Records and active in the 1980s and ea ...
collisions as in the south and east of England, but also because Europe is partitioned by mountain ranges such as the
Alps The Alps () ; german: Alpen ; it, Alpi ; rm, Alps ; sl, Alpe . are the highest and most extensive mountain range system that lies entirely in Europe, stretching approximately across seven Alpine countries (from west to east): France, Swi ...
. The
Po Valley The Po Valley, Po Plain, Plain of the Po, or Padan Plain ( it, Pianura Padana , or ''Val Padana'') is a major geographical feature of Northern Italy. It extends approximately in an east-west direction, with an area of including its Venetic e ...
(Pianura Padana) is one of the areas frequented with more tornadoes in the European continent than elsewhere. Located in the heart of Europe, between the Alps and the
Apennines The Apennines or Apennine Mountains (; grc-gre, links=no, Ἀπέννινα ὄρη or Ἀπέννινον ὄρος; la, Appenninus or  – a singular with plural meaning;''Apenninus'' (Greek or ) has the form of an adjective, which wou ...
, the collision between cold and warm air here during the summer months easily permits the growing of very strong thunderstorms. The most frequent tornadoes occur in the eastern section of the Po Plains. Parts of
Styria Styria (german: Steiermark ; Serbo-Croatian and sl, ; hu, Stájerország) is a state (''Bundesland'') in the southeast of Austria. With an area of , Styria is the second largest state of Austria, after Lower Austria. Styria is bordered to ...
(Steiermark) in
Austria Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populou ...
may be a tornado alley, and this state has had at least three F3 tornadoes since 1900. F3 and perhaps one F4 tornado have also occurred as far north as Finland.


Geographical occurrences

The United States has the most tornadoes of any country. Many of these form in an area of the central United States known as
Tornado Alley Tornado Alley is a loosely defined area of the central United States where tornadoes are most frequent. The term was first used in 1952 as the title of a research project to study severe weather in areas of Texas, Louisiana, Oklahoma, Kansas, S ...
. This area extends into Canada, particularly the prairie provinces and Ontario. Activity in Canada, however, is less frequent and intense than that of the US. Strong tornadoes occur in northern Mexico. A large region of South America is also characterized by storms that reach the level of supercells and produce intense hailstorms, floods, and tornadoes during the spring, summer, and early fall. The region recently dubbed as the Tornado Corridor (South America) is considered the second largest in the world in terms of the formation of extreme weather events. It covers most of central Argentina, southern Paraguay, southeastern Brazil, and Uruguay. Other areas of the world that have frequent strong tornadoes include Germany, the Czech Republic, Slovakia, Italy, Spain, China, and the
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
. Australia, France, Russia, areas of the Middle East, and Japan have a history of multiple damaging tornado events. Bangladesh and surrounding areas of eastern India suffer from a couple tornadoes annually of similar severity to stronger tornadoes in the US. These occur with a greater recurrence interval but over a smaller region. The annual human death toll from tornadoes in Bangladesh is estimated at 179 deaths per year, which is much greater than in the US. This is likely due to the density of population; poor quality of construction; lack of tornado safety knowledge; and lack of warnings—among other factors.


Location specifics


United States

The United States averaged 1,274 tornadoes per year from 2001 to 2011. April 2011 saw the most tornadoes recorded to date for any month in the US
National Weather Service The National Weather Service (NWS) is an agency of the United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the ...
's history: 875. It has more tornadoes yearly than any other country, and reports more violent F4 and F5 tornadoes than anywhere else. Tornadoes are common in many states but are most common to the west of the
Appalachian Mountains The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a mountain range, system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovicia ...
and to the east of the
Rockies The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico ...
. The Atlantic seaboard states:
North Carolina North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia and ...
,
South Carolina )'' Animis opibusque parati'' ( for, , Latin, Prepared in mind and resources, links=no) , anthem = " Carolina";" South Carolina On My Mind" , Former = Province of South Carolina , seat = Columbia , LargestCity = Charleston , LargestMetro = ...
,
Georgia Georgia most commonly refers to: * Georgia (country), a country in the Caucasus region of Eurasia * Georgia (U.S. state), a state in the Southeast United States Georgia may also refer to: Places Historical states and entities * Related to th ...
and
Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth are ...
, are also vulnerable, as well as
Florida Florida is a U.S. state, state located in the Southeastern United States, Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia (U.S. state), Geo ...
, though most Florida tornadoes are relatively weak, usually EF0 or EF1. The southern states are also highly impacted, in terms of casualties. More tornadoes occur in
Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...
than in any other US state, but the state that has the highest number of tornadoes per area is Florida. Tornadoes often occur along the edges of the
hurricane A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depe ...
s that strike the state. The state with the highest number of strong tornadoes per area is
Oklahoma Oklahoma (; Choctaw: ; chr, ᎣᎧᎳᎰᎹ, ''Okalahoma'' ) is a state in the South Central region of the United States, bordered by Texas on the south and west, Kansas on the north, Missouri on the northeast, Arkansas on the east, New ...
, while the neighboring state of
Kansas Kansas () is a state in the Midwestern United States. Its capital is Topeka, and its largest city is Wichita. Kansas is a landlocked state bordered by Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to ...
records the most EF4 and EF5 tornadoes in the country. Tornadoes can occur west of the
continental divide A continental divide is a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea, or else is endorheic, n ...
, but they are infrequent and usually relatively weak and short-lived. Recently, tornadoes have struck along the Pacific coast towns of Lincoln City, Oregon (1996); Sunnyvale, California (1998);
Port Orchard Port Orchard, part of Washington state's Puget Sound, is the strait that separates Bainbridge Island on the east from the Kitsap Peninsula on the west. It extends from Liberty Bay and Agate Pass in the north to Sinclair Inlet and Rich Passag ...
, Washington (2018); and downtown
Salt Lake City Salt Lake City (often shortened to Salt Lake and abbreviated as SLC) is the capital and most populous city of Utah, United States. It is the seat of Salt Lake County, the most populous county in Utah. With a population of 200,133 in 2020, th ...
, Utah (1999). The
California Central Valley The Central Valley is a broad, elongated, flat valley that dominates the interior of California. It is wide and runs approximately from north-northwest to south-southeast, inland from and parallel to the Pacific coast of the state. It covers ...
is an area of some frequency for tornadoes, albeit of very weak intensity. The deadliest U.S. tornado recorded is 18 March 1925,
Tri-State Tornado On March 18, 1925, one of the deadliest tornado outbreaks in recorded history generated at least twelve significant tornadoes and spanned a large portion of the midwestern and southern United States. In all, at least 751 people were ki ...
that swept across southeastern
Missouri Missouri is a state in the Midwestern region of the United States. Ranking 21st in land area, it is bordered by eight states (tied for the most with Tennessee): Iowa to the north, Illinois, Kentucky and Tennessee to the east, Arkansas to ...
, southern
Illinois Illinois ( ) is a state in the Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolitan areas include, Peoria and Rockf ...
, and southern
Indiana Indiana () is a U.S. state in the Midwestern United States. It is the 38th-largest by area and the 17th-most populous of the 50 States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th st ...
, that killed 695 people. The biggest
tornado outbreak __NOTOC__ A tornado outbreak is the occurrence of multiple tornadoes spawned by the same synoptic scale weather system. The number of tornadoes required to qualify as an outbreak typically are at least six to ten, with at least two rotational ...
on record—with 353 tornadoes for just days (including four EF5 and eleven EF4 tornadoes)—occurred starting on 25 April 2011 and intensifying on April, 26, and 27 (a record-breaking day), before ending on 28 April 2011, now referred to as the
2011 Super Outbreak The 2011 Super Outbreak was the largest, costliest, and one of the deadliest tornado outbreaks ever recorded, taking place in the Southern, Midwestern, and Northeastern United States from April 25–28, 2011, leaving catastrophic destruction ...
.


Canada

Canada annually experiences numerous tornadoes, although fewer than the United States. On average 62 are reported per year, but this number is expected to in fact be higher due to undetected tornadoes in large expanses of underpopulated areas.
NOAA The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditi ...
records a higher average of 100 per year in Canada. These storms cause tens of millions of dollars in damage. Most are weak F0 or F1 in intensity, but there are on average a few F2 or stronger that touch down each season. For example, the tornado frequency of
Southwestern Ontario Southwestern Ontario is a secondary region of Southern Ontario in the Canadian province of Ontario. It occupies most of the Ontario Peninsula bounded by Lake Huron, including Georgian Bay, to the north and northwest; the St. Clair River, Lake S ...
is about half that of the most tornado-prone areas of the central US plains. The last multiple tornado-related deaths in Canada were caused by a tornado in
Ear Falls, Ontario Ear Falls is a township located in Northwestern Ontario, Canada, on the banks of the English River, Lac Seul, Pakwash Lake and Wenesaga Lake. It is located along Highway 105, north of Highway 17 and Vermilion Bay, about halfway between Hi ...
on 9 July 2009, where 3 died, and the last killer tornado was on 3 August 2018 in Alonsa, Manitoba. The two deadliest tornadoes on Canadian soil were the
Regina Cyclone The Regina Cyclone, or Regina tornado of 1912, was a tornado that devastated the city of Regina, Saskatchewan, Canada, on Sunday, June 30, 1912. It remains the deadliest tornado in Canadian history with a total of 28 fatalities and about 300 ...
of 30 June 1912 (28 fatalities) and the
Edmonton Tornado The Edmonton tornado of 1987, an event also known as Black Friday to Edmontonians, was a powerful and devastating tornado that ripped through the eastern parts of Edmonton, Alberta, Canada and parts of neighbouring Strathcona County on the aft ...
of 31 July 1987 (27 fatalities). Both of these storms were rated an F4 on the Fujita scale. The city of Windsor was struck by strong tornadoes four times over 61 years (1946, 1953, 1974, 1997) ranging in strength from an F2 to F4. Canada's first official F5 tornado struck
Elie, Manitoba Elie is an unincorporated community recognized as a local urban district in the Rural Municipality of Cartier in the Canadian province of Manitoba. Geography The community is located approximately west of Winnipeg along the Trans-Canada Highw ...
on 22 June 2007. Tornadoes are most frequent in the provinces of
Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Terr ...
,
Saskatchewan Saskatchewan ( ; ) is a province in western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on the south by the U.S. states of Montana and North Da ...
,
Manitoba , image_map = Manitoba in Canada 2.svg , map_alt = Map showing Manitoba's location in the centre of Southern Canada , Label_map = yes , coordinates = , capital = Winn ...
, and Ontario.


Europe

The UK has the most annual tornadoes per land area per year, 0.14 per 1000 km2 (although these tornadoes are generally weak), and other European countries have a similar number of tornadoes per area. One notable tornado of recent years was the
tornado A tornado is a violently 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. It is often referred to as a twister, whirlwind or cyclone, altho ...
that struck Birmingham, United Kingdom, in July 2005. A row of houses was destroyed, but no one was killed. Europe as a whole has about 700 tornadoes per year. They are most common from June to August, especially in the inland, and rarest from January to March. Strong and violent tornadoes (F3–F5) do occur, especially in some of the interior areas and in the south, but are not as common as in parts of the US. As in the US, tornadoes are far from evenly distributed. Since 1900, deadly tornadoes have occurred in Austria, Belgium, Cyprus, Czech Republic, Finland, France, Germany, Italy, Lithuania, Malta, the Netherlands, Poland, Ukraine, Portugal, Romania, Russia, and the UK. The 1984 Ivanovo–Yaroslavl outbreak, with more than 400 fatalities and 213 injured, was the 20th century's deadliest tornado outbreak in Europe. It included at least one F5 and one F4.


Asia

Bangladesh and the eastern parts of India are very exposed to destructive tornadoes. Bangladesh, the Philippines, and Japan have the highest number of reported tornadoes in Asia. The single deadliest tornado ever recorded struck the
Manikganj District Manikganj ( bn, মানিকগঞ্জ ) is a district in central Bangladesh. It is a part of the Dhaka Division, In 1845 AD it was at first declared as a sub-division. It was at first, under Faridpur district (Faridpur Zila) then it was i ...
of Bangladesh on 26 April 1989, killing an estimated 1,300 people, injuring 12,000, and leaving approximately 80,000 people homeless. Five other recorded tornadic events have killed more than 500 people in Bangladesh, most recently on 13 May 1996 when a tornado swept through the Jamalpur and
Tangail Tangail ( bn, টাঙ্গাইল, ), is a major city within the Dhaka Division in central Bangladesh. It sits on the bank of the Louhajang River, north-west of Dhaka, the nation's capital. It is considered to be the main urban area of ...
districts, killing more than 600. China occasionally experiences destructive tornadoes. Storms producing multiple tornadoes and hail struck a densely populated area of farms and factories near the city of
Yancheng Yancheng () is a prefecture-level city in northeastern Jiangsu province, People's Republic of China. As the city with the largest jurisdictional area in Jiangsu, Yancheng borders Lianyungang to the north, Huai'an to the west, Yangzhou and Ta ...
in Jiangsu province, about 800 kilometers (500 miles) south of
Beijing, China } Beijing ( ; ; ), alternatively romanized as Peking ( ), is the capital of the People's Republic of China. It is the center of power and development of the country. Beijing is the world's most populous national capital city, with over 21 ...
. Throughout China, an estimated 100 tornadoes may occur per year with a few exceeding F4 in intensity, with activity most prevalent in eastern regions.


South America

South America has its own
tornado alley Tornado Alley is a loosely defined area of the central United States where tornadoes are most frequent. The term was first used in 1952 as the title of a research project to study severe weather in areas of Texas, Louisiana, Oklahoma, Kansas, S ...
, comprising areas in central and northern Argentina, southern and southeast Brazil, Uruguay, and part of Paraguay. It is considered the second-highest frequency tornado region in the world. Argentina has areas with high tornadic activity, and the strongest tornadoes in the southern hemisphere, such as the F5 in San Justo, Argentina, north of the city of Santa Fe, with winds that exceeded . In Brazil, one of the most remarkable events occurred on 24 May 2005 when an F3(EF3) multiple-vortex tornado struck the industrial district of the city of
Indaiatuba Indaiatuba is a municipality in the state of São Paulo in Brazil. It is part of the Metropolitan Region of Campinas. The population is 256,223 (2020 est.) in an area of . The elevation is . The city's name derives from the Tupi language Old ...
in the state of São Paulo.


Africa

Tornadoes do occur in extreme southern Africa (including the countries of
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...
,
Lesotho Lesotho ( ), officially the Kingdom of Lesotho, is a country landlocked as an enclave in South Africa. It is situated in the Maloti Mountains and contains the highest mountains in Southern Africa. It has an area of over and has a populatio ...
, and
Eswatini Eswatini ( ; ss, eSwatini ), officially the Kingdom of Eswatini and formerly named Swaziland ( ; officially renamed in 2018), is a landlocked country in Southern Africa. It is bordered by Mozambique to its northeast and South Africa to its no ...
). In October 2011 (i.e. in the spring), two people were killed and nearly 200 were injured after a tornado formed, near Ficksburg in the Free State; more than 1,000 shacks and houses were flattened. There is also the seasonal incidence of tornadoes in the coast of
western Africa West Africa or Western Africa is the westernmost region of Africa. The United Nations defines Western Africa as the 16 countries of Benin, Burkina Faso, Cape Verde, The Gambia, Ghana, Guinea, Guinea-Bissau, Ivory Coast, Liberia, Mali, Maurita ...
. These occur during the onset of the rainy season when tumultuous winds accompanied by sheets of rain as well as spectacular thunder and lightning batter the coast. The tornado generating storms were often welcomed by colonial settlers in the region since they dissipated extreme heat and
humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity de ...
during the last days of the dry season. Tornadoes are often embedded in the African
squall line A squall line, or more accurately a quasi-linear convective system (QLCS), is a line of thunderstorms, often forming along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front (which often are accomp ...
s, but they damage crops, and diminish any beneficial effect of its rains.


Oceania

Australia has about 16 tornadoes per year – excluding waterspouts, which are common. In New Zealand, a tornado hit the northern suburbs of
Auckland Auckland (pronounced ) ( mi, Tāmaki Makaurau) is a large metropolitan city in the North Island of New Zealand. The most populous urban area in the country and the fifth largest city in Oceania, Auckland has an urban population of about ...
on 3 May 2011, killing one and injuring at least 16 people.


Time of occurrence


Cyclonis systems

Tornadoes are most common in spring and least common in winter. The seasonal transition during autumn and spring promotes the development of
extratropical cyclone Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable of ...
s and frontal systems that support strong convective storms. Tornadoes are common in
landfall Landfall is the event of a storm moving over land after being over water. More broadly, and in relation to human travel, it refers to 'the first land that is reached or seen at the end of a journey across the sea or through the air, or the fact ...
ing
tropical cyclone A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Dep ...
s, where they are focused in the right poleward section of the cyclone. Tornadoes can be spawned as a result of eyewall mesovortices, which persist until landfall.


Seasonality

The time of year is a big factor in the intensity and frequency of tornadoes. On average, in the United States as a whole, the month with the most tornadoes is in May, followed by the months June, April, and July. There is no " tornado season" though, as tornadoes, including violent tornadoes and major outbreaks, can and do occur anywhere at any time of year if favorable conditions develop. Major tornado outbreaks have occurred every month of the year. The reason for the peak period for tornado formation in North America being skewed toward spring has much to do with temperature patterns in the U.S. Tornadoes often form when cool, polar air traveling southeastward from the Rockie Mountains overrides warm, moist, unstable
Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United St ...
air in the eastern states. Tornadoes tend to be commonly found in front of a cold front, along with heavy rains, hail, and damaging winds. Since both warm and cold major weather patterns collide in Spring, the conflict between the two air masses tends to the formation of tornado producing storms and supercells. As the weather warms across the country, the occurrence of tornadoes spreads northward. There is a second active tornado season of the year that usually appears in late September to mid-November. Autumn, like spring, is a time of the year when warm weather frequently alternates with cold weather, especially in the Midwest; but the season is not as active as it is during the springtime, and tornado frequencies are higher along the
Atlantic coastal plain The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Africa, Europe an ...
. On average, there are around 294 tornadoes throughout the United States during May, and as many as 543 tornadoes have been reported in May alone (in 2003). The months with the fewest tornadoes are usually December and January, although major tornado outbreaks can and sometimes do occur even in those months. In general, in the Midwestern and Plains states, springtime (especially the month of May) is the most active season for tornadoes, while in the far northern states (like
Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over to ...
and
Wisconsin Wisconsin () is a state in the upper Midwestern United States. Wisconsin is the 25th-largest state by total area and the 20th-most populous. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michi ...
), the peak tornado season is usually in the summer months (June and July). In the colder late autumn and winter months (from early December to late February), tornado activity is generally limited to the southern states, where warm Gulf of Mexico air can penetrate. July is the peak month in Austria, Finland, and Germany.


Diurnality

Tornado occurrence is highly dependent on the time of day because of
solar heating A solar thermal collector collects heat by absorbing sunlight. The term "solar collector" commonly refers to a device for solar hot water heating, but may refer to large power generating installations such as solar parabolic troughs and so ...
. Austria, Finland, Germany, and the United States' peak hour of occurrence is 5 pm, with roughly half of all tornado occurrence between 3 p.m. and 7 p.m. local time. Due to this being the time of peak atmospheric heating, and thus the maximum available energy for storms; some researchers, including Howard B. Bluestein of the
University of Oklahoma , mottoeng = "For the benefit of the Citizen and the State" , type = Public research university , established = , academic_affiliations = , endowment = $2.7billion (2021) , p ...
, have referred to this phenomenon as "five o'clock magic." Despite this, there have been several morning tornadoes reported, such as evidenced by the Gainesville Tornado of 1936 (one of the deadliest tornadoes in history) that occurred at 8:30 a.m. local time.


Common misconceptions

Tornado myths exist that may cause ill-conceived preparation, planning, and reactions to tornadoes. For instance: some people mistakenly believe that tornadoes only occur in the countryside. While it is true that the plains states are tornado-prone, tornadoes have been reported in every U.S. state, including
Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U. ...
and
Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only ...
. One likely reason tornadoes are so common in the central U.S. is that this is where Arctic air, cold fronts that have not been "weakened" yet first collide with warm tropical air from the
Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United St ...
. As these fronts head further east, they sometimes lose their strength as they travel over more warm air. For this reason, tornadoes are not as common on the East Coast as they are in the Midwest. However, they have happened on rare occasions, such as the F3 twister that struck Limerick Township, Pennsylvania near Philadelphia on 27 July 1994, the F2 twister that struck the northern suburbs of New York City on 12 July 2006, the EF2 twister in the borough of
Brooklyn Brooklyn () is a borough of New York City, coextensive with Kings County, in the U.S. state of New York. Kings County is the most populous county in the State of New York, and the second-most densely populated county in the United States, beh ...
on 8 August 2007, or the F4 twister that struck La Plata, Maryland on 28 April 2002. Another popular misconception is that tornadoes don't occur in mountainous areas, or that mountainous terrain will protect people from tornadoes. While the frequency of tornadoes is lower in mountainous areas compared to
Tornado Alley Tornado Alley is a loosely defined area of the central United States where tornadoes are most frequent. The term was first used in 1952 as the title of a research project to study severe weather in areas of Texas, Louisiana, Oklahoma, Kansas, S ...
, significant tornadoes can occur regularly in the southern Appalachian region of the United States and have even been documented at high altitudes along the
continental divide A continental divide is a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea, or else is endorheic, n ...
of Wyoming. In addition, tornado outbreaks occasionally occur around the southern Appalachian mountains, with the
1974 Super Outbreak The 1974 Super Outbreak was the second-largest tornado outbreak on record for a single 24-hour period, just behind the 2011 Super Outbreak. It was also the most violent tornado outbreak ever recorded, with 30 F4/F5 tornadoes confirmed. From Apr ...
and the
2011 Super Outbreak The 2011 Super Outbreak was the largest, costliest, and one of the deadliest tornado outbreaks ever recorded, taking place in the Southern, Midwestern, and Northeastern United States from April 25–28, 2011, leaving catastrophic destruction ...
directly affecting the southern Appalachian region.


Long-term trends

The reliable climatology of tornadoes is limited in geographic and temporal scope; only since 1976 in the United States and 2000 in Europe have thorough and accurate tornado statistics been logged. However, some trends can be noted in tornadoes causing significant damage in the United States, as somewhat reliable statistics on damaging tornadoes exist as far back as 1880. The highest incidence of violent tornadoes seems to shift from the Southeastern United States to the southern
Great Plains The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland in North America. It is located west of the Mississippi River and east of the Rocky Mountains, much of it covered in prairie, steppe, an ...
every few decades. Also, the 1980s seemed to be a period of unusually low tornado activity in the United States, and the number of multi-death tornadoes decreased every decade from the 1920s to the 1980s, suggesting a multi-decadal pattern of some sort.Grazulis, 196–198


See also

* List of tornadoes and tornado outbreaks *
List of F5 and EF5 tornadoes This is a list of tornadoes which have been officially or unofficially labeled as F5, EF5, T10-T11, IF5, or an equivalent rating, the highest possible ratings on the various tornado intensity scales. These scales – the Fujita scale, the Enhanc ...
* List of tornadoes by calendar day *
Tornadogenesis 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 pro ...


Notes


References


Further reading

* * * * * * *


External links


U.S. Severe Thunderstorm Climatology
( NSSL)
U.S. Tornado Climatology
( NCDC)
U.S. Tornado Climatology
(
University of Nebraska–Lincoln The University of Nebraska–Lincoln (Nebraska, NU, or UNL) is a public land-grant research university in Lincoln, Nebraska. Chartered in 1869 by the Nebraska Legislature as part of the Morrill Act of 1862, the school was known as the Univ ...
)
When and Where Do Tornadoes Occur?
(
National Atlas of the United States The ''National Atlas of the United States'' was an atlas published by the United States Department of the Interior from 1874 to 1997. Older editions were printed, but the most recent edition was available online. Since it is a publication of ...
) {{DEFAULTSORT:Tornado Climatology Tornado Natural disasters Climatology