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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, although the word cyclone is used in meteorology to name a weather system with a low-pressure area in the center around which, from an observer looking down toward the surface of the Earth, winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern. Tornadoes come in many shapes and sizes, and they are often visible in the form of a condensation funnel originating from the base of a cumulonimbus cloud, with a cloud of rotating debris and dust beneath it. Most tornadoes have wind speeds less than 180 kilometers per hour, are about 80 meters across, and travel several kilometers before dissipating. The most extreme tornadoes can attain wind speeds of more than 480 kilometers per hour (300 mph), are more than 3 kilometers (2 mi) in diameter, and stay on the ground for more than 100 km (62 mi).
In meteorology, a cyclone is a large air mass that rotates around a strong center of low atmospheric pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere as viewed from above. Cyclones are characterized by inward-spiraling winds that rotate about a zone of low pressure. The largest low-pressure systems are polar vortices and extratropical cyclones of the largest scale. Warm-core cyclones such as tropical cyclones and subtropical cyclones also lie within the synoptic scale. Mesocyclones, tornadoes, and dust devils lie within the smaller mesoscale. Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the tropical upper tropospheric trough during the summer months in the Northern Hemisphere. Cyclones have also been seen on extraterrestrial planets, such as Mars, Jupiter, and Neptune. Cyclogenesis is the process of cyclone formation and intensification. Extratropical cyclones begin as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones. These zones contract and form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, extratropical cyclones occlude as cold air masses undercut the warmer air and become cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the subtropical jet stream.
The United Kingdom straddles the higher mid-latitudes between 49° and 61°N on the western seaboard of Europe. Since the UK is always in or close to the path of the polar front jet stream, frequent changes in pressure and unsettled weather are typical. Many types of weather can be experienced in a single day. In general the climate of the UK is changeable, often cloudy especially in the more northerly areas of the country, with rain evenly distributed throughout the year.
An anticyclone is a weather phenomenon defined as a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere as viewed from above. Effects of surface-based anticyclones include clearing skies as well as cooler, drier air. Fog can also form overnight within a region of higher pressure.
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 killed and more than 2,298 were injured, making the outbreak the deadliest tornado outbreak, March 18 the deadliest tornado day, and 1925 the deadliest tornado year in U.S. history. The outbreak generated several destructive tornadoes in Missouri, Illinois, and Indiana on the same day, as well as significant tornadoes in Alabama and Kansas. In addition to confirmed tornadoes, there were undoubtedly others with lesser impacts, the occurrences of which have been lost to history.
A high-pressure area, high, or anticyclone, is an area near the surface of a planet where the atmospheric pressure is greater than the pressure in the surrounding regions. Highs are middle-scale meteorological features that result from interplays between the relatively larger-scale dynamics of an entire planet's atmospheric circulation.
Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere. Cyclogenesis is an umbrella term for at least three different processes, all of which result in the development of some sort of cyclone, and at any size from the microscale to the synoptic scale.
Hurricane Edith was the strongest hurricane to form during the 1971 Atlantic hurricane season and formerly the southernmost landfalling Category 5 hurricane on record in the Atlantic until 2007. Edith also stands as one of the only Category 5 Atlantic hurricanes to not have its name retired, next to 1953's Hurricane Carol, 1961's Hurricane Esther, 2005's Hurricane Emily, and 2019's Hurricane Lorenzo. Edith developed from a tropical wave on September 5 and quickly strengthened into a hurricane in the Caribbean Sea. Edith rapidly intensified on September 9 and made landfall on Cape Gracias a Dios as a Category 5 hurricane on the Saffir-Simpson Hurricane Scale. Being a category 5 hurricane, Edith peaked at only 943 mbar (hPa), making Edith the least intense category 5 Atlantic hurricane on record. It quickly lost intensity over Central America and after briefly entering the Gulf of Honduras it crossed the Yucatán Peninsula in Mexico. After moving across the Gulf of Mexico a trough turned the storm to the northeast and Edith, after having restrengthened while accelerating towards the coast, made landfall on Louisiana with winds of 105 mph (169 km/h) on September 16. Edith steadily weakened over land and dissipated over Georgia on September 18.
The Azores High also known as North Atlantic (Subtropical) High/Anticyclone or the Bermuda-Azores High, is a large subtropical semi-permanent centre of high atmospheric pressure typically found south of the Azores in the Atlantic Ocean, at the Horse latitudes. It forms one pole of the North Atlantic oscillation, the other being the Icelandic Low. The system influences the weather and climatic patterns of vast areas of North Africa, Western Asia, Southern Europe, and to a lesser extent, eastern North America. The aridity of the Sahara Desert and the summer drought of the Mediterranean Basin is due to the large-scale subsidence and sinking motion of air in the system. In its summer position, the high is centered near Bermuda, and creates a southwest flow of warm tropical air toward the East Coast of the United States. In summer, the Azores-Bermuda High is strongest. The central pressure hovers around 1024 mbar (hPa).
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 producing anything from cloudiness and mild showers to severe gales, thunderstorms, blizzards, and tornadoes. These types of cyclones are defined as large scale (synoptic) low pressure weather systems that occur in the middle latitudes of the Earth. In contrast with tropical cyclones, extratropical cyclones produce rapid changes in temperature and dew point along broad lines, called weather fronts, about the center of the cyclone.
The 2006 London tornado was a significant United Kingdom tornado spawned from a squall line moving over the city on 7 December 2006 at approximately 11:02 GMT. Its intensity is estimated to have been T5 on the TORRO scale, equating to F2 on the Fujita scale.
The March 1990 Central United States tornado outbreak affected portions of the United States Great Plains and Midwest regions from Iowa to Texas from March 11 to March 13, 1990. The outbreak produced at least 64 tornadoes across the region, including four violent tornadoes; two tornadoes, which touched down north and west of Wichita, Kansas, were both rated F5, including the tornado that struck Hesston. In Nebraska, several strong tornadoes touched down across the southern and central portion of the state, including an F4 tornado that traveled for 131 miles (211 km) making it the longest tracked tornado in the outbreak. Two people were killed in the outbreak, one each by the two F5 tornadoes in Kansas.
The December 1960 nor'easter was a significant early-season winter storm that impacted the Mid-Atlantic and New England regions of the United States. Moderate to heavy snowfall fell from West Virginia to eastern Maine, amounting to 10 in (25 cm) or more in parts of 13 states and peaking at 21.4 in (54 cm) at Newark, New Jersey. The storm was accompanied by strong winds, gusting to over 90 mph (140 km/h) in coastal New England, and left in its wake a dangerously cold air mass. The storm originated in a weak low pressure area which formed over the western Gulf of Mexico on December 10. A secondary low developed over South Carolina on the next day, supported by the merger of two troughs aloft. Sliding southeast of New England, the new storm explosively deepened to become a full-fledged nor'easter, with a minimum central air pressure of 966 mbar. It began to weaken over the Canadian Maritimes.
Tropical Storm Debra was the second of two tropical storms to hit the United States in the 1978 Atlantic hurricane season. The fourth named storm of the season, Debra developed from the interaction between a high-altitude cold low and a lower tropical wave in the Gulf of Mexico. Forming on August 25, it was upgraded to Tropical Storm Debra based on data from a Hurricane Hunter aircraft. As Debra approached the coast, it attained peak winds of 60 mph (95 km/h). The storm made landfall on the coast of Louisiana, east of the Texas border. Two deaths were caused by the storm. Debra weakened as it moved inland and ultimately dissipated on August 29 over Arkansas.
The following is a glossary of tornado terms. It includes scientific as well as selected informal terminology.
The 2015–16 North American winter was not as frigid across North America and the United States as compared to the 2013–14 and 2014–15 winters. This was mainly due to a strong El Niño, which caused generally warmer-then-average conditions. However, despite the warmth, significant weather systems still occurred, including a snowstorm and flash flooding in Texas at the end of December and a large tornado outbreak at the end of February. The main event of the winter season, by far and large, was when a crippling and historic blizzard struck the Northeastern United States in late January, dumping up to 3 feet of snow in and around the metropolitan areas. Several other smaller snow events affected the Northeast as well, but for the most part the heaviest snowstorms and ice stayed out further west, such as a severe blizzard in western Texas in late December, and a major late-season snowstorm in Colorado in mid-April.
2013–2014 Atlantic winter storms in Europe were a series of winter storms affecting areas of Atlantic Europe and beyond. The French Atlantic coastal regions, South West and Southern England, West Wales, Ireland, Spanish Atlantic coastal regions were especially affected by a "conveyor belt" series of high-precipitation storms and by high tides. Many storms were explosively deepened by a strong jet stream, many deepening below 950 hPa. The repeated formation of large deep lows over the Atlantic brought storm surges and large waves which coincided with some of the highest astronomical tides of the year and caused coastal damage. The low pressure areas brought heavy rainfalls which led to flooding, which became most severe over parts of England such as at the Somerset Levels. The repeated storms fit into a pattern of disturbed weather in the Northern Hemisphere, which saw from November 2013 a disturbance to the jet stream in the western Pacific, which propagated eastwards bringing a warm winter to Alaska, drought to California, and repeated cold air outbreaks to the eastern USA where the early 2014 North American cold wave resulted.
The winter of 1981–1982 in the United Kingdom was a severe cold wave that was formed in early December 1981 and lasted until mid-late January in 1982, and was one of the coldest Decembers recorded in the United Kingdom.
The 1913 United Kingdom tornado outbreak was an outbreak of Tornadoes, particularly over England and Wales, on 27 October 1913. The most notable tornadoes occurred in South Wales, where at least two tornadoes had winds of at least 160 miles per hour (260 km/h). This is equal to an F3 on the Fujita scale. One of the tornadoes, at Edwardsville, Merthyr Tydfil, resulted in 6 deaths and hundreds of injuries. This is the deadliest-known tornado to occur in the United Kingdom. Other notable tornadoes struck in Cheshire and Shropshire.
Anticyclone Hartmut was a storm that began on 22 February 2018, and brought a cold wave to Great Britain and Ireland. Anticyclone Hartmut also brought widespread unusually low temperatures and heavy snowfall to large areas. The cold wave combined with Storm Emma, part of the 2017–18 European windstorm season, which made landfall in southwest England and the south of Ireland on 2 March.
References
- 1 2 "European Severe Weather Database". www.eswd.eu.
- 1 2 3 Rowe, M. W.; Meaden, G. T. (1985). "Britain's Greatest Tornado Outbreak". Weather. 40 (8): 230–235. Bibcode:1985Wthr...40..230R. doi:10.1002/j.1477-8696.1985.tb06883.x.
- 1 2 3 Apsley, Miriam L.; Mulder, Kelsey J.; Schultz, David M. (2016). "Reexamining the United Kingdom's Greatest Tornado Outbreak: Forecasting the Limited Extent of Tornadoes along a Cold Front" (PDF). Weather and Forecasting. 31 (3): 853–875. Bibcode:2016WtFor..31..853A. doi:10.1175/WAF-D-15-0131.1.
- ↑ "23 November 1981: Tornado Outbreak - TheWeatherOutlook forum". www.theweatheroutlook.com.