A fictitious synoptic chart of an extratropical cyclone affecting Great Britain & Ireland. The blue and red arrows between isobars indicate the direction of the wind and its relative temperature, while the "L" symbol denotes the center of the "low". Note the occluded, cold and warm frontal boundaries. A surface weather analysis is a special type of Weather map that provides a view of Weather elements over a geographical area at a specified time based on information

Extratropical cyclones, sometimes called mid-latitude cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and horizontal gradients in temperature and dew point otherwise known as "baroclinic zones". In Meteorology, a cyclone refers to an area of closed circular fluid motion rotating in the same direction as the Earth. The synoptic scale in Meteorology (also known as large scale or cyclonic scale) is a horizontal length scale of the order of 1000 kilometres (about 620 A low pressure area, or " low " is a region where the Atmospheric pressure is lower in relation to the surrounding area A tropical cyclone is a storm system characterized by a low pressure center and numerous Thunderstorms that produce strong winds and Flooding Polar Cyclones (also known as polar vortices, Arctic cyclones, and sub-polar cyclones) are vast areas of low pressure which strengthen in the A surface weather analysis is a special type of Weather map that provides a view of Weather elements over a geographical area at a specified time based on information In Vector calculus, the gradient of a Scalar field is a Vector field which points in the direction of the greatest rate of increase of the scalar Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The dew point (sometimes spelled dewpoint) is the Temperature to which a given parcel of Air must be cooled at constant Barometric pressure, [1] Extratropical cyclones are the everyday phenomena which, along with anticyclones, drive the weather over much of the Earth, producing anything from cloudiness and mild showers to heavy gales and thunderstorms. In Meteorology, an anticyclone (that is opposite to a Cyclone) is a Weather phenomenon in which there is a descending movement of the air and Rain is Liquid precipitation. On Earth it is the condensation of atmospheric Water vapor into drops heavy enough to fall often making it to

## Terminology

Extratropical cyclones encompass a class of storms with many names. Although they are sometimes referred to as "cyclones", this is imprecise; cyclone applies to numerous types of low pressure areas. In Meteorology, a cyclone refers to an area of closed circular fluid motion rotating in the same direction as the Earth. The descriptor extratropical signifies that this type of cyclone generally occurs outside the tropics in the middle latitudes of Earth. Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the The term mid-latitude cyclones may be used because of where they form; "post-tropical cyclones" if extratropical transition has occurred. [1][2] Weather forecasters and the general public often describe them as "depressions" or "lows". Terms like frontal cyclone, frontal depression, frontal low, extratropical low, non-tropical low are often used as well.

Extratropical cyclones are classified mainly as baroclinic, because they form along zones of temperature and dewpoint gradient known as frontal zones. In Fluid dynamics, the baroclinity (sometimes called baroclinicity) is a measure of the Stratification in a fluid In Vector calculus, the gradient of a Scalar field is a Vector field which points in the direction of the greatest rate of increase of the scalar A weather front is a boundary separating two masses of air of different densities, and is the principal cause of meteorological phenomena. They can become barotropic late in their life cycle, when the distribution of heat around the cyclone becomes fairly uniform with its radius. In Meteorology, a barotropic atmosphere is one in which the pressure depends only on the density and vice versa so that isobaric surfaces (constant pressure surfaces

## Formation

Approximate areas of extratropical cyclone formation worldwide
An upper level jet streak. DIV areas are regions of divergence aloft, which will lead to surface convergence and aid cyclogenesis.

Extratropical cyclones form anywhere within the extratropical regions of the Earth (usually between 30° and 60° latitude from the equator), either through cyclogenesis or extratropical transition. Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the A study of extratropical cyclones in the Southern Hemisphere shows that between the 30th and 70th parallels, there are an average of 37 cyclones in existence during any 6-hour period. Southern Hemisphere is the half of a Planet that is South of the Equator —the word hemisphere literally means 'half ball' [3] A separate study in the Northern Hemisphere suggests that approximately 234 significant extratropical cyclones form each winter. Northern Hemisphere is the half of a Planet that is North of the Equator —the word hemisphere literally means 'half ball' [4]

### Cyclogenesis

Main article: Cyclogenesis

Extratropical cyclones form along linear bands of temperature/dewpoint gradient with significant vertical wind shear, and are thus classified as baroclinic cyclones. Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere (a low pressure area Wind shear, sometimes referred to as windshear or Wind gradient, is a difference in Wind speed and direction over a relatively Barotropic cyclones are those where Isotherms are parallel to height lines on a map at a constant pressure surface or at the surface parallel to Isobars. Initially, cyclogenesis, or low pressure formation, occurs along frontal zones near a favorable quadrant of a maximum in the upper level jetstream known as a jet streak, usually being the right rear and left front quadrants, where divergence ensues. Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere (a low pressure area A surface weather analysis is a special type of Weather map that provides a view of Weather elements over a geographical area at a specified time based on information Jet streams are fast flowing relatively narrow air currents found at the Tropopause, the transition between the Troposphere (where temperature decreases In Vector calculus, the divergence is an Operator that measures the magnitude of a Vector field &rsquos source or sink at a given point the This causes air to rush out from the top of the air column which in turn forces convergence in the low-level wind field and increased upward motion within the column. In the absence of a more specific context convergence denotes the approach toward a definite value as time goes on or to a definite point a common view or opinion or The increased upward motion causes surface pressures to lower as the upward air motion counteracts gravity, lessening the weight of the atmosphere (surface pressure) in that location, and thus strengthening the cyclone. In Meteorology, a cyclone refers to an area of closed circular fluid motion rotating in the same direction as the Earth. As the cyclone strengthens, the cold front sweeps towards the equator and moves around the back of the cyclone. The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the Meanwhile, its associated warm front progresses more slowly, as the cooler air ahead of the system is denser, and therefore more difficult to dislodge. A warm front is defined as the leading edge of an advancing mass of warm air it separates warm air from the colder air ahead The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different Later, the cyclones occlude as the poleward portion of the cold front overtakes a section of the warm front, forcing a tongue, or trowal, of warm air aloft. Eventually, the cyclone will become barotropically cold and begin to weaken.

A rapidly-falling atmospheric pressure is possible due to strong upper level forces on the system, and when pressures fall more than 1 millibar (0. 029 inHg) per hour, such a cyclone is sometimes referred to as a bomb. [5][6][7] These bombs rapidly drop in pressure to below 980 millibars (28. The bar (symbol bar) decibar (symbol dbar) and the millibar (symbol mbar, also mb are units of Pressure. 94 inHg) under favorable conditions such as near a natural temperature gradient like the Gulf Stream, or at a preferred quadrant of an upper level jet streak, where upper level divergence is best. Inches of mercury, inHg or "Hg is a measuring unit for Pressure. The Gulf Stream, together with its northern extension towards Europe the North Atlantic Drift, is a powerful warm and swift Atlantic Ocean current that The stronger the upper level divergence over the cyclone, the deeper the cyclone can become. Hurricane-force extratropical cyclones are most likely to form in the northern Atlantic and northern Pacific oceans in the months of December and January. [8] The lowest pressure measured from an extratropical cyclone in the United States was 951. The United States of America —commonly referred to as the 7 millibars (28. 10 inHg) on March 1, 1914 in Bridgehampton, New York. Events 86 BC - Lucius Cornelius Sulla, at the head of a Roman Republic army enters in Athens, removing the Tyrant Year 1914 ( MCMXIV) was a Common year starting on Thursday (link will display the full calendar of the Gregorian calendar (or a Common year Bridgehampton is a hamlet (and Census-designated place) in the South Fork of Suffolk County, New York, United States. Between January 4 and January 5, 1989, an extratropical cyclone south of Atlantic Canada deepened to 928 millibars (27. Events 46 BC - Titus Labienus defeats Julius Caesar in the Battle of Ruspina. Events 1477 - Battle of Nancy: Charles the Bold is killed and Burgundy becomes part of France. Year 1989 ( MCMLXXXIX) was a Common year starting on Sunday (link displays 1989 Gregorian calendar) 40 inHg), equivalent to a category 4 hurricane. The Saffir-Simpson Hurricane Scale is a classification used for most Western Hemisphere Tropical cyclones that exceed the intensities of Tropical depressions [9] In the Arctic, the average pressure for cyclones is 988 millibars (29. The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region is the smallest and shallowest of the world's five major 18 inHg) during the winter, and 1,000 millibars (29. 53 inHg) during the summer. [10]

### Extratropical transition

Cyclone Florence in the north Atlantic after completing its transition to an extratropical cyclone from a hurricane

Tropical cyclones often transform into extratropical cyclones at the end of their tropical existence, usually between 30° and 40° latitude, where there is sufficient forcing from upper-level troughs or shortwaves riding the Westerlies for the process of extratropical transition to begin. A tropical cyclone is a storm system characterized by a low pressure center and numerous Thunderstorms that produce strong winds and Flooding Earth's atmosphere (and its mechanics can often be described in Meteorology with very particular and specific terms The Westerlies or the Prevailing Westerlies are the prevailing winds in the Middle latitudes between 30 and 60 degrees Latitude, blowing from During extratropical transition, the cyclone begins to tilt back into the colder airmass with height, and the cyclone's primary energy source converts from the release of latent heat from condensation (from thunderstorms near the center) to baroclinic processes. The enthalpy of vaporization, (symbol \Delta{}_{v}H also known as the heat of vaporization or heat of evaporation, is the Energy required The low pressure system eventually loses its warm core and becomes a cold-core system. During this process, a cyclone in extratropical transition (known in Canada as the post-tropical stage)[11] will invariably form or connect with nearby fronts and/or troughs consistent with a baroclinic system. Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page Due to this, the size of the system will usually appear to increase, while the core weakens. However, after transition is complete, the storm may re-strengthen due to baroclinic energy, depending on the environmental conditions surrounding the system. The cyclone will also distort in shape, becoming less symmetric with time.

On rare occasions, an extratropical cyclone can transit into a tropical cyclone if it reaches an area of ocean with warmer waters and an environment with less vertical wind shear. The peak time of subtropical cyclogenesis (the midpoint of this transition) is in the months of September and October, when the difference between the temperature of the air aloft and the sea surface temperature is the greatest, leading to the greatest potential for instability. A subtropical cyclone is a Weather system that has some characteristics of a Tropical cyclone and some characteristics of an Extratropical cyclone. Sea surface temperature (SST is the water Temperature close to the surface [12] The process known as "tropical transition" involves the usually slow development of an extratropically cold core vortex into a tropical cyclone. [13][14]

## Structure

### Surface pressure/Wind distribution

QuikSCAT image of typical extratropical cyclones over the ocean. A weather front is a boundary separating two masses of air of different densities, and is the principal cause of meteorological phenomena. See also Earth Observing System European Remote-Sensing Satellite Note the maximum winds are on the outside of the occlusion.

The windfield of an extratropical cyclone constricts with distance in relation to surface level pressure, with the lowest pressure being found near the center, and the highest winds typically just on the cold/poleward side of warm fronts, occlusions, and cold fronts, where the pressure gradient force is highest. A cold front defined as the leading edge of a cooler and drier mass of air [15] The area north and west of the cold and warm fronts connected to extratropical cyclones is known as the cold sector, while the area south and east of its associated cold and warm fronts is known as the warm sector.

The wind flow around a large cyclone is counterclockwise in the northern hemisphere, and clockwise in the southern hemisphere, due to the Coriolis effect (this manner of rotation is generally referred to as cyclonic). A clockwise motion is one that proceeds 'like the Clock 's hands' from the top to the right then down and then to the left and back to the top In physics the Coriolis effect is an apparent deflection of moving objects when they are viewed from a Rotating frame of reference. Near this center, the pressure gradient force (from the pressure at the center of the cyclone compared to the pressure outside the cyclone) and the Coriolis force must be in an approximate balance for the cyclone to avoid collapsing in on itself as a result of the difference in pressure. The central pressure of the cyclone will lower with increasing maturity, while outside of the cyclone, the sea-level pressure is not very low; its typical value is around 1,013 millibars (29. 92 inHg), which is the average sea level pressure for Earth. In most extratropical cyclones, the part of the cold front ahead of the cyclone will develop into a warm front, giving the frontal zone (as drawn on surface weather maps) a wave-like shape. A surface weather analysis is a special type of Weather map that provides a view of Weather elements over a geographical area at a specified time based on information Due to their appearance on satellite images, extratropical cyclones can also be referred to as frontal waves early in their life cycle. In the United States, an old name for such a system is "warm wave". The United States of America —commonly referred to as the [16]

Once a cyclone occludes, a trough of warm air aloft, or "trowal" for short, will be caused by strong southerly winds on its eastern periphery rotating aloft around its northeast, and ultimately northwestern, periphery (also known as the warm conveyor belt), forcing a surface trough to continue into the cold sector on a similar curve to the occluded front. The trowal creates the portion of an occluded cyclone known as its comma head, due to the comma-like shape of the mid-tropospheric cloudiness that accompanies the feature. A comma ( ,   is a Punctuation mark It has the same shape as an Apostrophe or single closing Quotation mark in many typefaces but it differs It can also be the focus of locally heavy precipitation, with thunderstorms possible if the atmosphere along the trowal is unstable enough for convection. [17]

### Vertical structure

Extratropical cyclones slant back into colder air masses and strengthen with height, sometimes exceeding 30,000 feet (approximately 9 km) in depth. The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand [18] Above the surface of the earth, the air temperature near the center of the cyclone is increasingly colder than the surrounding environment. These characteristics are the direct opposite of those found in their tropical cyclones; thus, they are sometimes called "cold-core lows". A tropical cyclone is a storm system characterized by a low pressure center and numerous Thunderstorms that produce strong winds and Flooding [19] Various charts can be examined to check the characteristics of a cold-core system with height, such as the 700 millibars (20. 67 inHg) chart, which is at about 10,000 feet or 3,000 meters in height. Cyclone phase diagrams are used to tell whether a cyclone is tropical, subtropical, or extratropical. [20]

## Cyclone evolution

Norwegian model and Shapiro-Keyser model differences in frontal structure

There are two models of cyclone development and lifecycles in common use - the Norwegian model and the Shapiro-Keyser Model. The older of the models of Extratropical cyclone development is known as the Norwegian Cyclone Model, developed during and shortly after World War I within the [21]

### Norwegian cyclone model

Of the two theories on extratropical cyclone structure and life cycle, the older is the Norwegian Cyclone Model, developed during World War I. World War I (abbreviated WWI; also known as the First World War, the Great War, and the War to End All In this theory, cyclones develop as they move up and along a frontal boundary, eventually occluding and reaching a barotropically cold environment. [22] It was developed completely from surface-based weather observations, including descriptions of clouds found near frontal boundaries. This theory still retains merit, as it is a good description for extratropical cyclones over continental landmasses.

### Shapiro-Keyser model

A second competing theory for extratropical cyclone development over the oceans is the Shapiro-Keyser model, developed in 1990. [23] Its main differences with the Norwegian Cyclone Model are the fracture of the cold front, treating warm-type occlusions and warm fronts as the same, and allowing the cold front to progress through the warm sector perpendicular to the warm front. In Geometry, two lines or planes (or a line and a plane are considered perpendicular (or orthogonal) to each other if they form congruent This model was based on oceanic cyclones and their frontal structure, as seen in surface observations and in previous projects which used planes to determine the vertical structure of fronts across the northwest Atlantic. Overview Fixed-wing aircraft range from small training and recreational aircraft to Wide-body aircraft and military cargo aircraft.

#### Warm seclusion

A warm seclusion is the mature phase of the extratropical cyclone lifecycle. This was conceptualized after the ERICA field experiment of the late 1980s, which produced observations of intense marine cyclones that indicated an anomalously warm low-level thermal structure, secluded (or surrounded) by a bent-back warm front and a coincident chevron-shaped band of intense surface winds. ERICA, or the Experiment on Rapidly Intensifying Cyclones over the Atlantic, is a scientific field project that started in the winter of 1988 / 1989. [24] The Norwegian Cyclone Model, as developed by the Bergen School of Meteorology, largely observed cyclones at the tail end of their lifecycle and used the term occlusion to identify the decaying stages. [25]

Warm seclusions may have cloud-free, eye-like features at their center (reminiscent of tropical cyclones), significant pressure falls, hurricane force winds, and moderate to strong convection. The eye is a region of mostly calm Weather found at the center of strong Tropical cyclones The eye of a Storm is a roughly circular area and typically 30–65 km A tropical cyclone is a storm system characterized by a low pressure center and numerous Thunderstorms that produce strong winds and Flooding Convection in the most general terms refers to the movement of molecules within Fluids (i The most intense warm seclusions often attain pressures less than 950 millibars (28. 05 inHg) with a definitive lower to mid-level warm core structure. [24] A warm seclusion, the result of a baroclinic lifecycle, occurs at latitudes well poleward of the tropics.

As latent heat flux releases are important for their development and intensification, most warm seclusion events occur over the oceans; they may impact coastal nations with hurricane force winds and torrential rain. In the various subfields of Physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks An ocean (from Greek, ''Okeanos'' (Oceanus) is a major body of saline water, and a principal component of the Hydrosphere. Wind is the flow of Air or other Gases that compose an Atmosphere (including but not limited to the Earth's) Rain is Liquid precipitation. On Earth it is the condensation of atmospheric Water vapor into drops heavy enough to fall often making it to [23][26] Climatologically, the Northern Hemisphere sees warm seclusions during the cold season months, while the Southern Hemisphere may see a strong cyclone event such as this during all times of the year.

In all tropical basins, except the Northern Indian Ocean, the extratropical transition of a tropical cyclone may result in reintensification into a warm seclusion. For example, Hurricane Maria of 2005 reintensified into a strong baroclinic system and achieved warm seclusion status at maturity (or lowest pressure). Hurricane Maria was a Cape Verde-type hurricane which formed in September during the 2005 Atlantic hurricane season. [27]

## Motion

A February 24, 2007 radar image of a large Extratropical cyclonic storm system at its peak over the central United States (3 MB)

Extratropical cyclones are generally driven, or "steered", by deep westerly winds in a general west to east motion across both the Northern and Southern hemispheres of the Earth. Events 303 - Galerius, Roman Emperor, publishes his edict that begins the persecution of Christians in his portion of the Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. This general motion of atmospheric flow is known as "zonal". [28] Where this general trend is the main steering influence of an extratropical cyclone, it is known as a "zonal flow regime". Zonal flow is a meteorological term meaning that the general flow pattern is west to east along the earth's Latitude lines (as opposed

When the general flow pattern buckles from a zonal pattern to the meridional pattern,[29] a slower movement in a north or southward direction is more likely. Meridional flow patterns feature strong, amplified troughs and ridges, generally with more northerly and southerly flow. Meridional flow is a meteorological term meaning that the general flow pattern is north to south along the earth's Longitude lines (the opposite of Zonal flow

Changes in direction of this nature are most commonly observed as a result of a cyclone's interaction with other low pressure systems, troughs, ridges, or with anticyclones. A low pressure area, or " low " is a region where the Atmospheric pressure is lower in relation to the surrounding area A trough is an elongated region of relatively low Atmospheric pressure, often associated with fronts Unlike fronts there is not a universal symbol for A ridge is an elongated region of relatively high Atmospheric pressure, the opposite of a trough. In Meteorology, an anticyclone (that is opposite to a Cyclone) is a Weather phenomenon in which there is a descending movement of the air and A strong and stationary anticyclone can effectively block the path of an extratropical cyclone. Such blocking patterns are quite normal, and will generally result in a weakening of the cyclone, the weakening of the anticyclone, a diversion of the cyclone towards the anticyclones periphery, or a combination of all three to some extent depending on the precise conditions. Blocks in Meteorology are large scale patterns in the Atmospheric pressure field that are nearly stationary effectively "blocking" or redirecting migratory It is also common for an extratropical cyclone to strengthen as the blocking anticyclone or ridge weakens in these circumstances. [30]

Where an extratropical cyclone encounters another extratropical cyclone (or almost any other kind of cyclonic vortex in the atmosphere), the two may combine to become a "Binary cyclone", where the vorticies of the two cyclones rotate around each other (known as the "Fujiwhara effect"). V erification of the O rigins of R otation in T ornadoes Ex periment or VORTEX, is a field project that seeks to understand how a The Fujiwhara effect or Fujiwara interaction is a type of interaction between two nearby cyclonic vortices, causing them to appear to "orbit" This most often results in a merging of the two low pressure systems into a single extratropical cyclone, or can less commonly result in a mere change of direction of either one or both of the cyclones. [31] The precise results of such interactions depend on factors such as the size of the two cyclones, their strength, their distance from each other, and the prevailing atmospheric conditions around them.

## Effects

### General

Preferred region of snowfall in an extratropical cyclone

Extratropical cyclones can bring mild weather with a little rain and surface winds of 15–30 km/h (10–20 mph), or they can be cold and dangerous with torrential rain and winds exceeding 119 km/h (74 mph),[32] (sometimes referred to as windstorms in Europe). Wind is the flow of Air or other Gases that compose an Atmosphere (including but not limited to the Earth's) (For the South African airport with IATA code "KMH" see Johan Pienaar Airport. A European windstorm is a severe cyclonic storm that tracks across the North Atlantic towards northwestern Europe in the winter months The band of precipitation that is associated with the warm front is often extensive. In Meteorology, precipitation (also known as one class of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric A warm front is defined as the leading edge of an advancing mass of warm air it separates warm air from the colder air ahead In mature extratropical cyclones, an area known as the comma head on the northwest periphery of the surface low can be a region of heavy precipitation, frequent thunderstorms, and thundersnows. Thundersnow also known as a winter thunderstorm or a thunder snowstorm is a rare Thunderstorm with Snow falling as the primary precipitation Cyclones tend to move along a predictable path at a moderate rate of progress. During fall, winter, and spring, the atmosphere over continents can be cold enough through the depth of the troposphere to cause snowfall. Autumn (also known as fall in North American English) is one of the four Temperate Seasons Autumn marks the transition from Summer The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and almost all of its Water vapor and

### Severe weather

Squall lines, or solid bands of strong thunderstorms, can form ahead of cold fronts and lee troughs due to the presence of significant atmospheric moisture and strong upper level divergence, leading to hail and high winds. A trough is an elongated region of relatively low Atmospheric pressure, often associated with fronts Unlike fronts there is not a universal symbol for Hail is a form of precipitation which consists of balls or irregular lumps of ice (hailstones [33] When significant directional wind shear exists in the atmosphere ahead of a cold front in the presence of a strong upper level jet stream, tornado formation is possible. [34] Although tornadoes can form anywhere on Earth, the greatest number occur in the Great Plains in the United States, because downsloped winds off the north-south oriented Rocky Mountains, which can form a dryline, aid their development at any strength. The Great Plains are the broad expanse of Prairie and Steppe which lie east of the Rocky Mountains in the United States and Canada Mountain peaks of the Rocky Mountains The Rocky Mountains, often called the Rockies, are a Mountain range in western North America. The Fujita scale ( F-Scale) or Fujita-Pearson scale, is a scale for rating Tornado intensity based on the damage tornadoes inflict on human-built structures

Explosive development of extratropical cyclones can be sudden. The storm known in the UK as the "Great Storm of 1987" deepened to 953 millibars (28. The Great Storm of 1987 occurred on the night of 15 October to 16 October 1987, when an unusually strong weather system caused winds to hit much of 14 inHg) with a highest recorded wind of 220 km/h (137 mph), resulting in the loss of 19 lives, 15 million trees, widespread damage to homes and an estimated economic cost of £1. The Pound Sterling ( symbol £; ISO code: GBP) subdivided into 100 pence (singular penny) is the Currency 2 billion (US$2. The United States dollar ( sign:$; code: USD) is the unit of Currency of the United States; it has also been 3 billion). [35][36]

Although most tropical cyclones that become extratropical quickly dissipate or are absorbed by another weather system, they can still retain winds of hurricane or gale force. In 1954, Hurricane Hazel became extratropical over North Carolina as a strong Category 3 storm. Hurricane Hazel was the worst Hurricane of the 1954 Atlantic hurricane season and one of the worst hurricanes of the 20th century North Carolina ( is a state located on the Atlantic Seaboard in the southeastern United States The Columbus Day Storm of 1962, which evolved from the remains of Typhoon Freda, caused heavy damage in Oregon and Washington, with widespread damage equivalent to at least a Category 3. The Columbus Day Storm of 1962 (otherwise known as the Big Blow was an extratropical wave Cyclone that ranked among the most intense to strike the United States Pacific Oregon ( is a state in the Pacific Northwest region of the United States. Washington ( is a state in the Pacific Northwest region of the United States. In 2005, Hurricane Wilma began to lose tropical characteristics while still sporting Category 3-force winds (and became fully extratropical as a Category 1 storm). Hurricane Wilma was the most intense hurricane ever recorded in the Atlantic basin. [37]

## Historic storms

A violent storm during the Crimean War on November 14, 1854 wrecked 30 vessels, and sparked initial investigations into meteorology and forecasting in Europe. The Crimean War, also known in Russia as the Eastern War (Восточная война Vostochnaya Vojna) (March 1854–February 1856 was fought Events 1533 - Conquistadors from Spain under the leadership of Francisco Pizarro arrive in Cajamarca, Inca Year 1854 ( MDCCCLIV) was a Common year starting on Sunday (link will display the full calendar of the Gregorian Calendar (or a Common year In the United States, the Columbus Day Storm of 1962 led to Oregon's lowest measured pressure of 965. The Columbus Day Storm of 1962 (otherwise known as the Big Blow was an extratropical wave Cyclone that ranked among the most intense to strike the United States Pacific Oregon ( is a state in the Pacific Northwest region of the United States.hPa (28. 51 inHg), violent winds, and US\$170 million in damage (1964 dollars). [38] A rapidly strengthening storm struck Vancouver Island on October 11, 1984, and inspired the development of moored buoys off the western coast of Canada. Vancouver Island is a large Island in British Columbia, Canada, one of several North American regions named after George Vancouver, the British Events 1138 - A massive earthquake struck Aleppo, Syria. 1531 - Huldrych Zwingli is killed Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page [39] The Wahine disaster, New Zealand's most infamous maritime disaster, occurred during a major extratropical storm. The Wahine disaster occurred on 10 April 1968 when the TEV Wahine, a New Zealand inter-island Ferry of the Union Company

## References

1. ^ a b Dr. Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere (a low pressure area A European windstorm is a severe cyclonic storm that tracks across the North Atlantic towards northwestern Europe in the winter months The extratropical transition (XT technique is a system used to subjectively estimate the intensity of Tropical cyclones undergoing transition into Extratropical A nor'easter (also northeaster; see below is a macro-scale Storm along the East Coast of the United States and Atlantic Canada. A surface weather analysis is a special type of Weather map that provides a view of Weather elements over a geographical area at a specified time based on information The Storm of the Century, also known as the ’93 Superstorm, No-Name Hurricane, the White Hurricane, or the ( Great) Blizzard Thundersnow also known as a winter thunderstorm or a thunder snowstorm is a rare Thunderstorm with Snow falling as the primary precipitation A tropical cyclone is a storm system characterized by a low pressure center and numerous Thunderstorms that produce strong winds and Flooding Tropical cyclogenesis is the technical term describing the development and strengthening of a Tropical cyclone in the Atmosphere. DeCaria (2005-12-07). Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Events 43 BC - Marcus Tullius Cicero assassinated 1696 - Connecticut Route 108, one of the oldest highways ESCI 241 – Meteorology; Lesson 16 – Extratropical Cyclones. Department of Earth Sciences, Millersville University, Millersville, Pennsylvania. Retrieved on 2006-10-21. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1512 - Martin Luther joins the theological faculty of the University of Wittenberg.
2. ^ Robert Hart and Jenni Evans (2003). Synoptic Composites of the Extratropical Transition Lifecycle of North Atlantic TCs as Defined Within Cyclone Phase Space. American Meteorological Society. Retrieved on 2006-10-03. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 42 BC - First Battle of Philippi: Triumvirs Mark Antony and Octavian fight an indecisive battle with Caesar's
3. ^ Ian Simmonds and Kevin Keay (2000-02). Variability of Southern Hemisphere Extratropical Cyclone Behavior, 1958–97. American Meteorology Society (Allenpress Inc). Retrieved on 2006-10-20. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1740 - Maria Theresa takes the throne of Austria. France, Prussia, Bavaria and Saxony
4. ^ S. K. Gulev, O. Zolina, and S. Grigoriev (2001). Winter Storms in the Northern Hemisphere (1958–1999). CO2 Science. Retrieved on 2006-10-20. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1740 - Maria Theresa takes the throne of Austria. France, Prussia, Bavaria and Saxony
5. ^ Jack Williams (2005-05-20). Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Events 325 - The First Council of Nicaea &ndash the first Ecumenical Council of the Christian Church is held Bomb cyclones ravage northwestern Atlantic. USA Today. Retrieved on 2006-10-04. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 610 - Heraclius arrives by ship from Africa at Constantinople, overthrows Byzantine Emperor Phocas
6. ^ American Meteorological Society Glossary - Bomb. Allen Press Inc. (2000-06). Retrieved on 2006-10-03. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 42 BC - First Battle of Philippi: Triumvirs Mark Antony and Octavian fight an indecisive battle with Caesar's
7. ^ Frederick Sanders and John R. Gyakum (October 1980). "Synoptic-Dynamic Climatology of the "Bomb"" (PDF). Monthly Weather Review 108 (10). Monthly Weather Review is a publication of the American Meteorological Society.
8. ^ Joseph M. Sienkiewicz, Joan M. Von Ahn, and G. M. McFadden (2005-07-18). Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Events 390 BC - Roman - Gaulish Wars Battle of the Allia - a Roman army is defeated by raiding Gauls, Hurricane Force Extratropical Cyclones. American Meteorology Society. Retrieved on 2006-10-21. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1512 - Martin Luther joins the theological faculty of the University of Wittenberg.
9. ^ JeffMasters (2006-02-15). Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 590 - Khosrau II is crowned as king of Persia 1637 - Ferdinand III becomes Holy Roman Emperor Flying into a record Nor'easter. JeffMasters' Blog on Wunderground.Com. Retrieved on 2006-10-04. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 610 - Heraclius arrives by ship from Africa at Constantinople, overthrows Byzantine Emperor Phocas
10. ^ A cyclone statistics for the Arctic based on European Centre re-analysis data (Abstract). Springer, Wien, AUTRICHE (1986). Retrieved on 2006-10-04. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 610 - Heraclius arrives by ship from Africa at Constantinople, overthrows Byzantine Emperor Phocas
11. ^ Glossary of Hurricane Terms. Canadian Hurricane Center (2003-07-10). Year 2003 ( MMIII) was a Common year starting on Wednesday of the Gregorian calendar. Events 48 BC - Battle of Dyrrhachium, Julius Caesar barely avoids a catastrophic defeat to Pompey in Macedonia. Retrieved on 2006-10-04. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 610 - Heraclius arrives by ship from Africa at Constantinople, overthrows Byzantine Emperor Phocas
12. ^ David M. Roth (2002-02-15). See also 2002 (disambiguation Year 2002 ( MMII) was a Common year starting on Tuesday of the Gregorian calendar. Events 590 - Khosrau II is crowned as king of Persia 1637 - Ferdinand III becomes Holy Roman Emperor A Fifty year History of Subtropical Cyclones. Hydrometeorological Prediction Center. Retrieved on 2006-10-04. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 610 - Heraclius arrives by ship from Africa at Constantinople, overthrows Byzantine Emperor Phocas
13. ^ Michelle L. Stewart, COAPS, Tallahassee, FL; and M. A. Bourassa (2006-04-25). Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1607 - Eighty Years' War: The Dutch fleet destroys the anchored Spanish fleet at Gibraltar. Cyclogenesis and Tropical Transition in decaying frontal zones. American Meteorological Society Conference. Retrieved on 2006-10-24. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 69 - Second Battle of Bedriacum, forces under Antonius Primus the commander of the Danube armies loyal to Vespasian, defeat
14. ^ Christopher A. Davis; Lance F. Bosart (2004-11). The TT Problem - Forecasting the Tropical Transition of Cyclones (PDF). American Meteorological Society Journals Online. Retrieved on 2006-10-24. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 69 - Second Battle of Bedriacum, forces under Antonius Primus the commander of the Danube armies loyal to Vespasian, defeat
15. ^ WW2010 - Pressure Gradient Force. University of Illinois (1999-09-02). Year 1999 ( MCMXCIX) was a Common year starting on Friday (link will display full 1999 Gregorian calendar) Events 44 BC - Pharaoh Cleopatra VII of Egypt declares her son co-ruler as Ptolemy XV Caesarion. Retrieved on 2006-10-11. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1138 - A massive earthquake struck Aleppo, Syria. 1531 - Huldrych Zwingli is killed
16. ^ The Atmosphere in motion: Pressure & mass. Ohio State University (2006-04-26). Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1467 - The miraculous image in Our Lady of Good Counsel appear in Genazzano, Italy. Retrieved on 2006-10-04. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 610 - Heraclius arrives by ship from Africa at Constantinople, overthrows Byzantine Emperor Phocas
17. ^ What is a TROWAL?. [St. Louis University] (Unknown). Retrieved on 2006-11-02. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1570 - A Tidal wave in the North Sea devastates the coast from Holland to Jutland, killing more than 1000
18. ^ Andrea Lang (2006-04-20). Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1303 - The University of Rome La Sapienza is instituted by Pope Boniface VIII. Mid-Latitude Cyclones: Vertical Structure. University of Wisconsin-Madison Department of Atmospheric and Oceanic Sciences. Retrieved on 2006-10-03. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 42 BC - First Battle of Philippi: Triumvirs Mark Antony and Octavian fight an indecisive battle with Caesar's
19. ^ Robert Hart (2003-02-18). Year 2003 ( MMIII) was a Common year starting on Wednesday of the Gregorian calendar. Events 3102 BC - Epoch (origin of the Kali Yuga. 1229 - The Sixth Crusade: Frederick II Holy Cyclone Phase Analysis and Forecast: Help Page. Florida State University Department of Meteorology. Retrieved on 2006-10-03. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 42 BC - First Battle of Philippi: Triumvirs Mark Antony and Octavian fight an indecisive battle with Caesar's
20. ^ Robert Hart (2006-10-04). Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 610 - Heraclius arrives by ship from Africa at Constantinople, overthrows Byzantine Emperor Phocas Cyclone phase evolution: Analyses & Forecasts. Florida State University Department of Meteorology. Retrieved on 2006-10-03. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 42 BC - First Battle of Philippi: Triumvirs Mark Antony and Octavian fight an indecisive battle with Caesar's
21. ^ David M. Roth (2005-12-15). Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Events 533 - Byzantine general Belisarius defeats the Vandals, commanded by King Gelimer, at the Battle of Unified Surface Analysis Manual. Hydrometeorological Prediction Center (NOAA). Retrieved on 2006-10-11. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1138 - A massive earthquake struck Aleppo, Syria. 1531 - Huldrych Zwingli is killed
22. ^ Shaye Johnson (2001-09-25). Year 2001 ( MMI) was a Common year starting on Monday according to the Gregorian calendar. Events 303 - On a voyage preaching the Gospel, Saint Fermin of Pamplona is beheaded in Amiens, France The Norwegian Cyclone Model. University of Oklahoma, School of Meteorology. Retrieved on 2006-10-11. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1138 - A massive earthquake struck Aleppo, Syria. 1531 - Huldrych Zwingli is killed
23. ^ a b David M. Schultz and Heini Werli (2001-01-05). Year 2001 ( MMI) was a Common year starting on Monday according to the Gregorian calendar. Events 1477 - Battle of Nancy: Charles the Bold is killed and Burgundy becomes part of France. Determining Midlatitude Cyclone Structure and Evolution from the Upper-Level Flow. Cooperative Institute for Mesoscale Meteorological Studies. Retrieved on 2006-10-09. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 768 - Carloman I and Charlemagne are crowned Kings of The Franks.
24. ^ a b Ryan N. Maue (2006-04-25). Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1607 - Eighty Years' War: The Dutch fleet destroys the anchored Spanish fleet at Gibraltar. Warm seclusion cyclone climatology. American Meteorological Society Conference. Retrieved on 2006-10-06. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 105 BC - Battle of Arausio: The Cimbri inflict the heaviest defeat on the Roman army of Gnaeus Mallius Maximus
25. ^ Lars Bärring (2003-12-11). Year 2003 ( MMIII) was a Common year starting on Wednesday of the Gregorian calendar. Events 359 - Honoratus, the first known Prefect of the City of Constantinople, takes office Wind Throw Damages on Forests - Frequency and Associated Pressure Patterns 1961–1990 and in a Future Climate Scenario. Department of Geography and Ecosystems Analysis, Lund University. Retrieved on 2006-10-30. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 637 - Antioch surrenders to the Muslim forces under Rashidun Caliphate after the Battle of Iron bridge.
26. ^ Jeff Masters (2006-02-14). Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 842 - Charles the Bald and Louis the German swear the Oaths of Strasbourg in the French and German Blizzicanes. JeffMasters' Blog on Wunderground.Com. Retrieved on 2006-11-01. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 996 - Emperor Otto III issues a deed to Gottschalk Bishop of Freising which is the oldest known document using the name Ostarrîchi
27. ^ Richard J. Pasch; Eric S. Blake (2006-02-08). Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 421 - Constantius III becomes co- Emperor of the Western Roman Empire. Tropical Cyclone Report - Hurricane Maria. National Hurricane Center (NOAA). Retrieved on 2006-10-30. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 637 - Antioch surrenders to the Muslim forces under Rashidun Caliphate after the Battle of Iron bridge.
28. ^ American Meteorological Society Glossary - Zonal Flow. Allen Press Inc. (2000-06). Retrieved on 2006-10-03. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 42 BC - First Battle of Philippi: Triumvirs Mark Antony and Octavian fight an indecisive battle with Caesar's
29. ^ American Meteorological Society Glossary - Meridional Flow. Allen Press Inc. (2000-06). Retrieved on 2006-10-03. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 42 BC - First Battle of Philippi: Triumvirs Mark Antony and Octavian fight an indecisive battle with Caesar's
30. ^ Anthony R. Lupo; Phillip J. Smith (1997-05-02). Year 1997 ( MCMXCVII) was a Common year starting on Wednesday (link will display full 1997 Gregorian calendar Events 1194 - King Richard I of England gives Portsmouth its first Royal Charter. The Interactions between a Midlatitude Blocking Anticyclone and Synoptic-Scale Cyclones That Occurred during the Summer Season. Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana. Retrieved on 2006-10-21. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1512 - Martin Luther joins the theological faculty of the University of Wittenberg.
31. ^ B. Ziv; P. Alpert (2003-11-20). Year 2003 ( MMIII) was a Common year starting on Wednesday of the Gregorian calendar. Events 284 - Diocletian was chosen as Roman Emperor. 762 - Bögü Khan of the Uyghurs, Theoretical and Applied Climatology - Rotation of mid-latitude binary cyclones: a potential vorticity approach. Springer Wien (ISSN 0177-798X (Print) 1434-4483 (Online)). Retrieved on 2006-10-21. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1512 - Martin Luther joins the theological faculty of the University of Wittenberg.
32. ^ Joan Von Ahn; Joe Sienkiewicz; Greggory McFadden; (2005-04). Mariners Weather Log, Vol 49, No. 1. Voluntary Observing Ship Program. Retrieved on 2006-10-04. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 610 - Heraclius arrives by ship from Africa at Constantinople, overthrows Byzantine Emperor Phocas
33. ^ WW2010 - Squall Lines. University of Illinois (1999-09-02). Year 1999 ( MCMXCIX) was a Common year starting on Friday (link will display full 1999 Gregorian calendar) Events 44 BC - Pharaoh Cleopatra VII of Egypt declares her son co-ruler as Ptolemy XV Caesarion. Retrieved on 2006-10-21. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1512 - Martin Luther joins the theological faculty of the University of Wittenberg.
34. ^ Tornadoes: Nature's Most Violent Storms. National Severe Storms Laboratory (NOAA) (2002-03-13). See also 2002 (disambiguation Year 2002 ( MMII) was a Common year starting on Tuesday of the Gregorian calendar. Events 1138 - Cardinal Gregorio Conti is elected Antipope as Victor IV, succeeding Anacletus II. Retrieved on 2006-10-21. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1512 - Martin Luther joins the theological faculty of the University of Wittenberg.
35. ^ The Great Storm of 1987. Met Office. Retrieved on 2006-10-30. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 637 - Antioch surrenders to the Muslim forces under Rashidun Caliphate after the Battle of Iron bridge.
36. ^ Bill McGuire (2005-12-22). Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Events 1790 - The Turkish fortress of Izmail is stormed and captured by Suvorov and his Russian armies What we should fear in 2006. Channel 4 News. Retrieved on 2006-10-30. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 637 - Antioch surrenders to the Muslim forces under Rashidun Caliphate after the Battle of Iron bridge.
37. ^ Richard J. Pasch; Eric S. Blake;, Hugh D. Cobb III; and David P Roberts (2006-01-12). Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 475 - Basiliscus becomes Byzantine Emperor, with a coronation ceremony in the Hebdomon palace in Constantinople Tropical Cyclone Report - Hurricane Wilma. National Hurricane Center (NOAA). Retrieved on 2006-10-11. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1138 - A massive earthquake struck Aleppo, Syria. 1531 - Huldrych Zwingli is killed
38. ^ George Taylor and Raymond R. Hatton. The 1962 Windstorm. Retrieved on 2006-11-25. Events 1034 - Máel Coluim mac Cináeda, King of Scots dies Donnchad, the
39. ^ S. G. P. Skey and M. D. Miles. Advances in Buoy Technology for Wind/Wave Data Collection and Analysis. Retrieved on 2006-11-25. Events 1034 - Máel Coluim mac Cináeda, King of Scots dies Donnchad, the

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