Tornado climatology
Encyclopedia
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
north into arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...
areas, and has no major east-west mountain range to block air flow between these two areas. In the middle latitudes
Middle latitudes
The middle latitudes are between 23°26'22" North and 66°33'39" North, and between 23°26'22" South and 66°33'39" South latitude, or, the Earth's temperate zones between the tropics and the Arctic and Antarctic. The prevailing winds in the middle latitudes are often very strong...
, where most tornadoes of the world occur, the Rocky Mountains
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...
block moisture and buckle the atmospheric flow
Prevailing winds
Prevailing winds are winds that blow predominantly from a single general direction over a particular point on Earth's surface. The dominant winds are the trends in direction of wind with the highest speed over a particular point on the Earth's surface. A region's prevailing and dominant winds...
, forcing drier air at mid-levels of the troposphere
Troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....
due to downsloped winds, and causing cyclogenesis downstream to the east of the mountains. Downsloped winds off the Rockies force the formation of a dry line
Dry line
A dry line separates moist air from the Gulf of Mexico and dry desert air from the south-western states . The dry line is an important factor in severe weather frequency in the Great Plains of North America...
when the flow aloft is strong, while the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
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. A large portion of these tornadoes form in an area of the central United States
Central United States
The Central United States is sometimes conceived as between the Eastern United States and Western United States as part of a three-region model, roughly coincident with the Midwestern United States plus the western and central portions of the Southern United States; the term is also sometimes used...
known as Tornado Alley
Tornado Alley
Tornado Alley is a colloquial and popular media term that most often refers to the area of the United States where tornadoes are most frequent. Although an official location is not defined, the area between the Rocky Mountains and Appalachian Mountains is usually associated with it.The areas...
. This area extends into Canada, particularly Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
and the Prairie Provinces. Strong tornadoes also occur in northern Mexico.
The United States averaged 1,274 tornadoes per year in the last decade. The Netherlands has the highest average number of recorded tornadoes per area of any country (more than 20, or 0.0013 per sq mi (0.00048 per km²), annually), followed by the UK (around 33, or 0.00035 per sq mi (0.00013 per km²), per year), but most are small and cause minor damage. In absolute number of events, ignoring area, the UK experiences more tornadoes than any other European country, excluding waterspouts.
Tornadoes kill an average of
52 people per year in Bangladesh, the most in the world. This is due to their high population density, poor quality of construction, lack of tornado safety knowledge, as well as other factors. Other areas of the world that have frequent tornadoes include South Africa, parts of Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
, Paraguay
Paraguay
Paraguay , officially the Republic of Paraguay , is a landlocked country in South America. It is bordered by Argentina to the south and southwest, Brazil to the east and northeast, and Bolivia to the northwest. Paraguay lies on both banks of the Paraguay River, which runs through the center of the...
, and southern Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
, as well as portions of Europe, Australia and New Zealand, and far eastern Asia.
The severity of tornadoes is commonly measured by the Enhanced Fujita Scale
Enhanced Fujita Scale
The Enhanced Fujita Scale rates the strength of tornadoes in the United States based on the damage they cause.Implemented in place of the Fujita scale introduced in 1971 by Ted Fujita, it began operational use on February 1, 2007. The scale has the same basic design as the original Fujita scale:...
, which scales tornado intensity from EF0 to EF5 by wind speed and the amount of damage they do to human environments. These judgements are always made after the tornado has dissipated and its damage trail is carefully studied by weather professionals.
Tornadoes are most common in spring and least common in winter. Since autumn and spring are transitional periods (warm to cool and vice versa) there are more chances of cooler air meeting with warmer air, resulting in thunderstorms. Tornadoes are focused in the right poleward section of landfall
Landfall (meteorology)
Landfall is the event of a tropical cyclone or a waterspout coming onto land after being over water. When a waterspout makes landfall it is reclassified as a tornado, which can then cause damage inland...
ing tropical cyclone
Tropical cyclone
A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...
s, which tend to occur in the late summer and autumn. Tornadoes can also be spawned
as a result of eyewall mesovortices, which persist until landfall. Favorable conditions can occur any time of the year.
Tornado occurrence is highly dependent on the time of day, because of solar heating. Worldwide, most tornadoes occur in the late afternoon, between 3 pm and 7 pm local time, with a peak near 5 pm. Destructive tornadoes can occur at any time of day. The Gainesville Tornado of 1936, one of the deadliest tornadoes in history, occurred at 8:30 am local time.
Geography
The United States has the most tornadoes of any country, seeing about four times the activity estimated in all of Europe. Many of these form in an area of the central United States known as Tornado AlleyTornado Alley
Tornado Alley is a colloquial and popular media term that most often refers to the area of the United States where tornadoes are most frequent. Although an official location is not defined, the area between the Rocky Mountains and Appalachian Mountains is usually associated with it.The areas...
. This area extends into Canada, particularly Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
and the Prairie Provinces; however, activity in Canada is less than that of the US. The Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
has the highest average number of tornadoes per square mile in the world (at least 20 recorded per year). The UK
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
also has a very high tornado density (more than 33 tornadoes reported annually), but most are small and result in minor damage.
Bangladesh
Bangladesh
Bangladesh , officially the People's Republic of Bangladesh is a sovereign state located in South Asia. It is bordered by India on all sides except for a small border with Burma to the far southeast and by the Bay of Bengal to the south...
and surrounding areas of eastern India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
suffer from tornadoes of lesser severity to those in the US with more regularity than any other region in the world. However, these occur with greater recurrence interval, and tend to be under-reported due to the scarcity of media coverage in a third-world country. The annual human death toll from tornadoes in Bangladesh is about 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 other factors.
Other areas of the world that have frequent strong tornadoes include parts of Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
and southern Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
, as well as South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. A fair number of weak and occasionally strong tornadoes occur annually in Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
, Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
and the Philippines. Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
, areas of the Middle East
Middle East
The Middle East is a region that encompasses Western Asia and Northern Africa. It is often used as a synonym for Near East, in opposition to Far East...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, Bangladesh
Bangladesh
Bangladesh , officially the People's Republic of Bangladesh is a sovereign state located in South Asia. It is bordered by India on all sides except for a small border with Burma to the far southeast and by the Bay of Bengal to the south...
and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
have a history of multiple damaging tornado events.
Tornadoes in the USA
The United States averaged 1,274 tornadoes per year in the last decade, with about 1000 tornadoes so far in 2011. April 2011 saw the most tornadoes ever recorded for any month in the US National Weather ServiceNational Weather Service
The National Weather Service , once known as the Weather Bureau, is one of the six scientific agencies that make up the National Oceanic and Atmospheric Administration of the United States government...
's history, 875; the previous record was only 542 in one month. 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
Appalachian Mountains
The Appalachian Mountains #Whether the stressed vowel is or ,#Whether the "ch" is pronounced as a fricative or an affricate , and#Whether the final vowel is the monophthong or the diphthong .), often called the Appalachians, are a system of mountains in eastern North America. The Appalachians...
and to the east of the Rockies
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...
. The Atlantic seaboard states - North Carolina
North Carolina
North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...
, South Carolina
South Carolina
South Carolina is a state in the Deep South of the United States that borders Georgia to the south, North Carolina to the north, and the Atlantic Ocean to the east. Originally part of the Province of Carolina, the Province of South Carolina was one of the 13 colonies that declared independence...
, Georgia
Georgia (U.S. state)
Georgia is a state located in the southeastern United States. It was established in 1732, the last of the original Thirteen Colonies. The state is named after King George II of Great Britain. Georgia was the fourth state to ratify the United States Constitution, on January 2, 1788...
and Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
- are also vulnerable, as well as Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
. The areas most vulnerable to tornadoes are the Southern Plains and Florida, though most Florida tornadoes are relatively weak. The Southern USA is one of the worst affected regions in terms of casualties.
Tornado reports have been officially collated since 1950. These reports have been gathered by the National Climatic Data Center
National Climatic Data Center
The United States National Climatic Data Center in Asheville, North Carolina is the world's largest active archive of weather data. The center became established in late 1951, with the move into the new facility occurring in early 1952....
(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.
Common misconceptions
Some people mistakenly believe that tornadoes only occur in the countryside. This is hardly the case. While it is true that the plains statesGreat Plains
The Great Plains are a broad expanse of flat land, much of it covered in prairie, steppe and grassland, which lies west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S...
are the most tornado-prone places in the nation, it should be noted that tornadoes have been reported in every U.S state, including Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
and Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
. One likely reason why tornadoes are so common in the central U.S is because this is where Arctic air first collides with warm tropical air from the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
where the cold front has not been "weakened" yet. As it heads further east, however, it is possible for the front to lose its strength as it travels over more warm air. Therefore, tornadoes are not as common on the East Coast
East Coast of the United States
The East Coast of the United States, also known as the Eastern Seaboard, refers to the easternmost coastal states in the United States, which touch the Atlantic Ocean and stretch up to Canada. The term includes the U.S...
as they are in the Midwest. However, they have happened on rare occasion, such as the F2 twister that struck the northern suburbs of New York City
New York City
New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...
on July 12, 2006, or the EF2 twister in parts of Brooklyn, New York on August 8, 2007.
Tornadoes can occur west of the continental divide
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, not connected to the open sea...
, but they are infrequent and usually relatively weak and short-lived. Recently tornadoes have struck the Pacific coast town of Lincoln City
Lincoln City, Oregon
Lincoln City is a city in Lincoln County, Oregon, United States. It is named after the county. The population was 7,930 at the 2010 census.- History :...
, Oregon (1996); Sunnyvale
Sunnyvale, California
Sunnyvale is a city in Santa Clara County, California, United States. It is one of the major cities that make up the Silicon Valley located in the San Francisco Bay Area...
, California (1998); and downtown Salt Lake City
Salt Lake City, Utah
Salt Lake City is the capital and the most populous city of the U.S. state of Utah. The name of the city is often shortened to Salt Lake or SLC. With a population of 186,440 as of the 2010 Census, the city lies in the Salt Lake City metropolitan area, which has a total population of 1,124,197...
, Utah (1999) (see Salt Lake City Tornado
Salt Lake City Tornado
The 1999 Salt Lake City tornado was a very rare tornado that occurred in Salt Lake City, Utah on August 11, 1999, during an unusually strong summer monsoon season...
). The California Central Valley
California Central Valley
California's Central Valley is a large, flat valley that dominates the central portion of California. It is home to California's most productive agricultural efforts. The valley stretches approximately from northwest to southeast inland and parallel to the Pacific Ocean coast. Its northern half is...
is an area of some frequency for tornadoes, albeit of weak intensity. Though tornadoes that occur on the Western Seaboard typically are weak, more powerful, damaging tornadoes can occur, such as a tornado that occurred on May 22, 2008 in Perris, California. http://articles.latimes.com/2008/may/23/local/me-weather23 More tornadoes occur in Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
than in any other US state.
The state which has the highest number of tornadoes per unit area is Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
, although most of the tornadoes in Florida are weak tornadoes of F0 or F1 intensity. A number of Florida's tornadoes occur along the edge of hurricanes that strike the state. The state with the highest number of strong tornadoes per unit area is Oklahoma
Oklahoma
Oklahoma is a state located in the South Central region of the United States of America. With an estimated 3,751,351 residents as of the 2010 census and a land area of 68,667 square miles , Oklahoma is the 28th most populous and 20th-largest state...
. The neighboring state of Kansas
Kansas
Kansas is a US state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa Native American tribe, which inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south...
is another particularly notorious tornado state. It records the most F4 and F5 tornadoes in the country.
Tornadoes in Canada
CanadaCanada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
also experiences numerous tornadoes, although fewer than the United States. In Canada, at least 80-100 tornadoes occur annually (with many more likely undetected in large expanses of unpopulated areas), causing tens of millions of dollars
Canadian dollar
The Canadian dollar is the currency of Canada. As of 2007, the Canadian dollar is the 7th most traded currency in the world. It is abbreviated with the dollar sign $, or C$ to distinguish it from other dollar-denominated currencies...
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
Southwestern Ontario is a subregion of Southern Ontario in the Canadian province of Ontario, centred on the city of London. It extends north to south from the Bruce Peninsula on Lake Huron to the Lake Erie shoreline, and east to south-west roughly from Guelph to Windsor. The region had a population...
is about half that of the most prone areas of the central US plains. The last multiple tornado-related deaths in Canada were caused by a tornado in Ear Falls, Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
, on July 9, 2009, where 3 died, and the last killer tornado was on August 21, 2011 in Goderich, Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
. The two deadliest tornadoes on Canadian soil were the Regina Cyclone
Regina Cyclone
The Regina Cyclone is the popular name for a tornado that devastated the city of Regina, Saskatchewan, Canada on June 30, 1912. At about 4:50 p.m., green funnel clouds formed and touched down south of the city, tearing a swath through the residential area between Wascana Lake and Victoria Avenue...
of June 30, 1912 (28 fatalities) and the Edmonton Tornado
Edmonton Tornado
The Edmonton Tornado, an event also known as Black Friday to Edmontonians, was a powerful and devastating tornado that ripped through the eastern part of Edmonton, Alberta, Canada and parts of neighbouring Strathcona County on the afternoon of Friday, July 31, 1987.The tornado remained on the...
of July 31, 1987 (27 fatalities). Both of these storms were rated an F4 on the Fujita scale. The city of Windsor
Windsor, Ontario
Windsor is the southernmost city in Canada and is located in Southwestern Ontario at the western end of the heavily populated Quebec City – Windsor Corridor. It is within Essex County, Ontario, although administratively separated from the county government. Separated by the Detroit River, Windsor...
, Ontario was struck by strong tornadoes four times within a 61-year span (1946, 1953 and 1974 and 1997) ranging in strength from an F2 to F4. Canada's first official F5 tornado struck Elie
Elie, Manitoba
Elie is the largest community in the Rural Municipality of Cartier in the Canadian province of Manitoba. The town of approximately 550 people is located approximately west of Winnipeg along the Trans-Canada Highway. The Assiniboine River forms the northern boundary of the municipality of...
, Manitoba on June 22, 2007
Elie, Manitoba Tornado
The Elie, Manitoba Tornado was an F5 tornado that struck the town of Elie, Manitoba, Canada, on June 22, 2007. While several houses were leveled, no one was injured or killed by the tornado. Two well-built homes in the town were swept clean off of their foundations, justifying the F5...
. At least two other tornadoes in Saskatchewan in earlier parts of the 20th century are suspected as F5.
Most common provinces for tornadoes are Manitoba, Alberta, Saskachewan and Ontario. But Windsor, Ontario and Winnipeg, Manitoba are the most tornado prone provinces in Canada.
Tornadoes Outside North America
Tornadoes do occur throughout the world as well; the most tornado-prone region of the world (outside North AmericaNorth America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
), as measured by number of reported tornadoes per unit area, is the Netherlands, followed by the United Kingdom (especially England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
). Bangladesh
Bangladesh
Bangladesh , officially the People's Republic of Bangladesh is a sovereign state located in South Asia. It is bordered by India on all sides except for a small border with Burma to the far southeast and by the Bay of Bengal to the south...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
, Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, Estonia
Estonia
Estonia , officially the Republic of Estonia , is a state in the Baltic region of Northern Europe. It is bordered to the north by the Gulf of Finland, to the west by the Baltic Sea, to the south by Latvia , and to the east by Lake Peipsi and the Russian Federation . Across the Baltic Sea lies...
, and portions of Uruguay
Uruguay
Uruguay ,officially the Oriental Republic of Uruguay,sometimes the Eastern Republic of Uruguay; ) is a country in the southeastern part of South America. It is home to some 3.5 million people, of whom 1.8 million live in the capital Montevideo and its metropolitan area...
also have pockets of high tornadic activity. Occasional strong tornadoes occur in Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, and portions of Paraguay
Paraguay
Paraguay , officially the Republic of Paraguay , is a landlocked country in South America. It is bordered by Argentina to the south and southwest, Brazil to the east and northeast, and Bolivia to the northwest. Paraguay lies on both banks of the Paraguay River, which runs through the center of the...
, Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
and Portugal
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
(such as the F3/T7 of Castelo Branco on November 6, 1954, which killed 5 and injured 220). Tornadoes have recently hit South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
and parts of Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...
in 2001 as well, and on April 4, 2006, a rare F2 tornado hit northwestern Israel, causing significant damage and injuries. Approximately 170 tornadoes are reported per year on land in Europe. One notable tornado of recent years was the tornado
Birmingham Tornado (UK)
The Birmingham Tornado was one of the strongest tornadoes recorded in the United Kingdom in nearly 30 years, occurring on 28 July 2005 in the suburbs of Birmingham. It formed on a day when strong tornadoes were expected to develop across the Midlands and eastern England...
which struck Birmingham, United Kingdom, in July 2005. A row of houses was destroyed, but no one was killed. A strong F3 (T7) Tornado hit the small town Micheln in Saxony-Anhalt, Germany on July 23, 2004 leaving 6 people injured and more than 250 buildings massively damaged.
Frequency of occurrence
Tornadoes can form in any month, providing the conditions are favorable. For example, a freak tornado hit South St. Louis County Missouri on January 1, 2011, causing pockets of heavy damage to a modest area before dissipating. The temperature was unseasonably warm that day. They are least common during the winter and most common in spring. Since autumn and spring are transitional periods (warm to cool and vice versa) there are more chances of cooler air meeting with warmer air, resulting in thunderstorms. Tornadoes in the late summer and fall can also be caused by hurricane landfall.Not every thunderstorm
Thunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
, supercell
Supercell
A supercell is a thunderstorm that is characterized by the presence of a mesocyclone: a deep, continuously-rotating updraft. For this reason, these storms are sometimes referred to as rotating thunderstorms...
, squall line
Squall
A squall is a sudden, sharp increase in wind speed which is usually associated with active weather, such as rain showers, thunderstorms, or heavy snow. Squalls refer to an increase in the sustained winds over a short time interval, as there may be higher gusts during a squall event...
, or tropical cyclone
Tropical cyclone
A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...
will produce a tornado. Precisely the right atmospheric conditions are required for the formation of even a weak tornado. On the other hand, 700 or more tornadoes a year are reported in the contiguous United States.
On average, the United States experiences 100,000 thunderstorms each year, resulting in more than 1,200 tornadoes and approximately 50 deaths per year. The deadliest U.S. tornado recorded is the March 18, 1925, Tri-State Tornado
Tri-State Tornado
The Tri-State Tornado of Wednesday, March 18, 1925, was the deadliest tornado in U.S. history. With 695 confirmed fatalities, the tornado killed more than twice as many as the second deadliest, the 1840 Great Natchez Tornado...
that swept across southeastern Missouri
Missouri
Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...
, southern Illinois
Illinois
Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...
and southern Indiana
Indiana
Indiana is a US state, admitted to the United States as the 19th on December 11, 1816. It is located in the Midwestern United States and Great Lakes Region. With 6,483,802 residents, the state is ranked 15th in population and 16th in population density. Indiana is ranked 38th in land area and is...
, killing 695 people. The biggest tornado outbreak
Tornado outbreak
While there is no single agreed upon definition, generally at least 6-10 tornadoes produced by the same synoptic scale weather system is considered a tornado outbreak. The tornadoes usually occur within the same day, or continue into the early morning hours of the succeeding day, and within the...
on record—with 353 tornadoes over the course of just 3 1/2 days, including four F5 and eleven F4 tornadoes—occurred starting on April 25, 2011 and intensifying on April 26 and especially the record-breaking day of April 27 before ending on April 28. It is named properly, April 25–28, 2011 tornado outbreak
April 25–28, 2011 tornado outbreak
An extremely large and violent tornado outbreak, the largest tornado outbreak ever recorded, and popularly known as the 2011 Super Outbreak, occurred from April 25 to 28, 2011. The outbreak affected the Southern, Midwestern, and Northeastern United States, leaving catastrophic destruction in...
but often called the second Super Outbreak. Previously, the record was 148 tornadoes, dubbed the (original) Super Outbreak
Super Outbreak
The Super Outbreak is the second largest tornado outbreak on record for a single 24-hour period, just behind the tornado outbreak of April 25–28, 2011...
. Another such significant storm system was the Palm Sunday tornado outbreak of 1965, which affected the United States Midwest on April 11, 1965. A series of continuous tornado outbreaks is known as a tornado outbreak sequence
Tornado outbreak sequence
A tornado outbreak sequence is a period of continuous or nearly continuous high tornado activity consisting of a series of tornado outbreaks over multiple days with no or very few days lacking tornado outbreaks....
, with significant occurrences in May 1917, 1930, 1949, and 2003.
Diurnality
Tornado occurrence is highly dependent on the time of day.Austria
Austria
Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...
, Finland
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, and the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
' peak hour of occurrence is 5 p.m., 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
University of Oklahoma
The University of Oklahoma is a coeducational public research university located in Norman, Oklahoma. Founded in 1890, it existed in Oklahoma Territory near Indian Territory for 17 years before the two became the state of Oklahoma. the university had 29,931 students enrolled, most located at its...
, have referred to this phenomenon as "five o'clock magic." Despite this, there are several morning tornadoes reported, like the Seymour
Seymour, Texas
Seymour is a city in and the county seat of Baylor County, Texas, United States. The population was 2,740 as of the 2010 Census.-Geography:Seymour is located at ....
, Texas one in April 1980.
Seasonality
The time of year is a big factor of the intensity and frequency of tornadoes. On average, in the United States as a whole, the month with the most tornadoes is 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 in every month of the year.July is the peak month in Austria, Finland, and Germany. On average, there are around 294 tornadoes throughout the United States during the month of May, and as many as 543 tornadoes have been reported in the month of 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
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...
and Wisconsin
Wisconsin
Wisconsin is a U.S. state located in the north-central United States and is part of the Midwest. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michigan to the northeast, and Lake Superior to the north. Wisconsin's capital is...
), 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 it is possible for warm Gulf of Mexico air to penetrate.
The reason for the peak period for tornado formation being in the spring has much to do with temperature patterns in the U.S. Tornadoes often form when cool, polar air traveling southeastward from the Rockies overrides warm, moist, unstable Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
air in the eastern states. Tornadoes therefore tend to be commonly found in front of a cold front, along with heavy rains, hail, and damaging winds. Since both warm and cold weather are common during the springtime, the conflict between these two air masses tends to be most common in the spring. As the weather warms across the country, the occurrence of tornadoes spreads northward. Tornadoes are also common in the summer and early fall because they 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, occurrences are found mostly in the Gulf states and Florida during winter (although there have been some notable exceptions). Interestingly, there is a second active tornado season of the year, late October to mid-November. Autumn, like spring, is a time of the year when warm weather alternates with cold weather frequently, 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 as opposed to the Midwest. They usually appear in late summer.
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 StatesSoutheastern United States
The Southeastern United States, colloquially referred to as the Southeast, is the eastern portion of the Southern United States. It is one of the most populous regions in the United States of America....
to the southern Great Plains
Great Plains
The Great Plains are a broad expanse of flat land, much of it covered in prairie, steppe and grassland, which lies west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S...
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.
See also
- Tornado intensity and damageTornado intensity and damageThe Fujita scale and the Enhanced Fujita Scale rate tornadoes by damage caused. The Enhanced Fujita Scale was an upgrade to the older Fujita scale, with engineered wind estimates and better damage descriptions, but was designed so that a tornado rated on the Fujita scale would receive the same...
- Tornado recordsTornado recordsThis article lists various tornado records. The most extreme tornado in recorded history was the Tri-State Tornado, which roared through parts of Missouri, Illinois, and Indiana on March 18, 1925. It was likely an F5, though tornadoes were not ranked on any scale in that era...
- List of tornadoes and tornado outbreaks
- List of F5 and EF5 tornadoes
- TornadogenesisTornadogenesisTornadogenesis is the process by which a tornado forms. There are many types of tornadoes, and each type of tornado can have several different methods of formation. Scientific study is ongoing, as some aspects of tornado formation remain a mystery....
- Tornado mythsTornado mythsDespite the fact that many misconceptions about tornadoes are no longer prevalent, many still remain. This can be attributed to many factors, including stories and news reports told by people unfamiliar with tornadoes, sensationalism by news media and the presentation of incorrect information in...
External links
- When and Where Do Tornadoes Occur? (National Atlas of the United StatesNational Atlas of the United StatesThe National Atlas of the United States is an online atlas published by the United States Department of the Interior.Since it is a publication of the United States Government, the atlas and the maps contained therein are in the public domain....
)