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Encyclopedia > Extratropical cyclone
A fictitious synoptic chart of an extratropical cyclone affecting the UK & Ireland. The blue arrows between isobars indicate the direction of the wind, while the "L" symbol denotes the center of the "low". Note the occluded, cold and warm frontal boundaries.
A fictitious synoptic chart of an extratropical cyclone affecting the UK & Ireland. The blue arrows between isobars indicate the direction of the wind, while the "L" symbol denotes the center of the "low". Note the occluded, cold and warm frontal boundaries.

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".[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. Image File history File links Uk-cyclone-2. ... Image File history File links Uk-cyclone-2. ... The word isobar derives from the two ancient Greek words, ισος (isos), meaning equal, and βαρος (baros), meaning weight. In meteorology, an isobar is a line of equal or constant pressure on a graph, plot, or map; an isopleth of pressure. ... A surface weather analysis for the United States on October 21, 2006. ... Radar image of a tropical cyclone in the northern hemisphere. ... synoptic literally means an overall view - hence Synoptic Gospels. ... A large low-pressure system swirls off the southwestern coast of Iceland, illustrating the maxim that nature abhors a vacuum. ... Cyclone Catarina, a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004 Hurricane and Typhoon redirect here. ... Polar cyclones (also known as Arctic Cyclones) are vast areas of low pressure. ... A surface weather analysis for the United States on October 21, 2006. ... Horizontal line (use sparingly)d grade for the grade or gradient of roads and other geographic features. ... Fig. ... Dew on a spider web The dew point or dewpoint of a given parcel of air is the temperature to which the parcel must be cooled, at constant barometric pressure, for the water vapor component to condense into water, called dew. ... In meteorology, an anticyclone (i. ... For the singer, see Rain (singer). ... A shelf cloud associated with a heavy or severe thunderstorm over Enschede, The Netherlands. ...

Contents

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. The descriptor extratropical signifies that this type of cyclone generally occurs outside the tropics in the middle latitudes of Earth. 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". Radar image of a tropical cyclone in the northern hemisphere. ... Latitude, usually denoted symbolically by the Greek letter phi, , gives the location of a place on Earth north or south of the equator. ...


Extratropical cyclones are classified mainly as baroclinic, because they form along zones of temperature and dewpoint gradient. They can become barotropic late in their life cycle, when the distribution of heat around the cyclone becomes fairly uniform with its radius. It has been suggested that Baroclinic instability and Baroclinic vector be merged into this article or section. ... Horizontal line (use sparingly)d grade for the grade or gradient of roads and other geographic features. ... A barotropic atmosphere is one in which the density depends only on the pressure, so that isobaric surfaces are also surfaces of constant density. ...

Formation

Approximate areas of extratropical cyclone formation worldwide
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.
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. 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.[3] A separate study in the Northern Hemisphere suggests that approximately 234 significant extratropical cyclones form each winter.[4] Image File history File links Download high-resolution version (1999x1000, 525 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Extratropical cyclone ... Image File history File links Download high-resolution version (1999x1000, 525 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Extratropical cyclone ... Image File history File links Jetstreak. ... Image File history File links Jetstreak. ... Latitude, usually denoted symbolically by the Greek letter phi, , gives the location of a place on Earth north or south of the equator. ... World map showing the equator in red For other uses, see Equator (disambiguation). ... The Southern Hemisphere is the half of a planets surface (or celestial sphere) that is south of the equator (the word hemisphere literally means half ball). On Earth it contains five continents (Antarctica, Australia, most of South America, parts of Africa and Asia) as well as four oceans (South... The Northern Hemisphere is the half of a planets surface (or celestial sphere) that is north of the equator (the word hemisphere literally means half ball). On the Earth, the Northern Hemisphere contains most of the land and about 88-90% of the human population. ... Winter is one of the four seasons of temperate zones. ...


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. Initially, cyclogenesis, or low pressure formation, occurs along frontal zones near a favorable quadrant of the upper level jetstream, usually being the right rear and left front quadrants, where divergence ensues. 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. 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. As the cyclone strengthens, the cold front sweeps towards the equator and moves around the back of the cyclone. Meanwhile, its associated warm front progresses more slowly, as the cooler air ahead of the system is denser, and therefore more difficult to dislodge. 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. Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere. ... Wind shear is a difference in wind speed or direction between two points in the atmosphere. ... 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. ... Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere. ... A surface weather analysis for the United States on October 21, 2006. ... Jet streams are fast flowing, confined air currents found in the atmosphere at around 12 km above the surface of the Earth, just under the tropopause. ... In vector calculus, the divergence is an operator that measures a vector fields tendency to originate from or converge upon a given point. ... 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 toward a fixed or equilibrium state. ... Image:Tagesgang-luftdruck. ... Radar image of a tropical cyclone in the northern hemisphere. ... World map showing the equator in red For other uses, see Equator (disambiguation). ... A surface weather analysis for the United States on October 21, 2006. ... In physics, Density is defined as mass m per unit volume V. Mathematically, it is expressed as where, in SI units: ρ (rho) is the density of the substance, measured in kg m-3 m is the mass of the substance, measured in kg v is the volume of the substance... A surface weather analysis for the United States on October 21, 2006. ...


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 (28.94 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. 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 951.7 millibars (28.10 inHg) on March 1, 1914 in Bridgehampton, New York. Between January 4 and January 5, 1989, an extratropical cyclone south of Atlantic Canada deepened to 928 millibars (27.40 inHg), equivalent to a category 4 hurricane.[9] In the Arctic, the average pressure for cyclones is 988 millibars (29.18 inHg) during the winter, and 1,000 millibars (29.53 inHg) during the summer.[10] Image:Tagesgang-luftdruck. ... The bar (symbol bar) and the millibar (symbol mbar, also mb) are units of pressure. ... Pressure is the application of force to a surface, and the concentration of that force in a given area. ... For the album by Ocean Colour Scene, see North Atlantic Drift (album) The Gulf Stream is orange and yellow in this representation of water temperatures of the Atlantic. ... March 1 is the 60th day of the year in the Gregorian calendar (61st in leap years). ... 1914 (MCMXIV) was a common year starting on Thursday (see link for calendar). ... Bridgehampton is a census-designated place located in Suffolk County, New York. ... January 4 is the 4th day of the year in the Gregorian calendar. ... January 5 is the 5th day of the year in the Gregorian calendar. ... 1989 (MCMLXXXIX) was a common year starting on Sunday of the Gregorian calendar. ... The Saffir-Simpson Hurricane Scale is a scale classifying most Western Hemisphere tropical cyclones that exceed the levels of tropical depression and tropical storm and thereby become hurricanes; the categories it divides hurricanes into are distinguished by the intensities of their respective sustained winds. ... Arctic Region NASA Arctic sea ice imagery, 2005 The Arctic Ocean, located mostly in the Arctic north polar region, is the smallest of the worlds five oceans and the shallowest. ...


Extratropical transition

Cyclone Florence in the north Atlantic after completing its transition to an extratropical cyclone from a hurricane
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. 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 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. 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. Image File history File links Download high-resolution version (7200x7200, 6310 KB) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Download high-resolution version (7200x7200, 6310 KB) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Cyclone Catarina, a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004 Hurricane and Typhoon redirect here. ... Earths atmosphere (and its mechanics) can often be described in meteorology with very particular and specific terms. ... The westerlies are the prevailing winds in the middle latitudes between 30 and 60 degrees latitude, blowing from the high pressure area in the horse latitudes towards the poles. ... The heat of vaporization is a physical property of substances. ...


On rare occasions, an extratropical cyclone can transition 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.[12] A subtropical cyclone is a weather system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. ... Annual mean sea surface temperature for the World Ocean. ...


Structure

Surface pressure/Wind distribution

QuikSCAT image of typical extratropical cyclones over the ocean. Note the maximum winds are on the outside of the occlusion.
QuikSCAT image of typical extratropical cyclones over the ocean. 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.[13] 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). 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. 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".[14] Image File history File links Quikscatcyclone. ... Image File history File links Quikscatcyclone. ... The QuikSCAT (Quick Scatterometer) is an earth-observing satellite that provides wind speed and direction information over oceans to NOAA.It is a quick recovery mission to fill the gap created by the loss of data from the NASA Scatterometer (NSCAT) that was lost in June 1997. ... The pressure gradient force is the force that is usually responsible for accelerating a parcel of air from a high atmospheric pressure region to a low pressure region, resulting in wind. ... A clockwise motion is one that proceeds like the clocks hands: from the top to the right, then down and then to the left, and back to the top. ... In the inertial frame of reference (upper part of the picture), the black object moves in a straight line. ... Sea-level pressure or mean sea-level pressure (MSL or MSLP) is the standard that different weather stations employ to compare barometric pressure readings, which are made in inches of mercury. ... In meteorology, a weather front is a boundary between two air masses with differing characteristics (e. ... A surface weather analysis for the United States on October 21, 2006. ...


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. It can also be the focus of locally heavy precipitation, with thunderstorms possible if the atmosphere along the trowal is unstable enough for convection.[15] A comma ( , ) is a punctuation mark. ...


Vertical structure

Extratropical cyclones slant back into colder air masses and strengthen with height, sometimes exceeding 30,000 feet (approximately 9 km) in depth.[16] 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".[17] 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.[18] km redirects here. ... Cyclone Catarina, a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004 Hurricane and Typhoon redirect here. ...


Cyclone evolution

Norwegian cyclone and Shapiro-Keyser model differences in frontal structure
Norwegian cyclone 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. [19] Image File history File links Download high-resolution version (1312x649, 18 KB) Hydrometeorological Prediction Center, Camp Springs, MD Web site: http://www. ... Image File history File links Download high-resolution version (1312x649, 18 KB) Hydrometeorological Prediction Center, Camp Springs, MD Web site: http://www. ...


Norwegian cyclone model

Of the two theories on extratropical cyclone structure and life cycle, the oldest is the Norwegian Cyclone Model, developed during World War I. In this theory, cyclones develop as they move up and along a frontal boundary, eventually occluding and reaching a barotropically cold environment.[20] 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. Combatants Allied Powers: Russian Empire France British Empire Italy United States Central Powers: Austria-Hungary German Empire Ottoman Empire Bulgaria Commanders Nicholas II Aleksei Brusilov Georges Clemenceau Joseph Joffre Ferdinand Foch Robert Nivelle Herbert Henry Asquith Sir Douglas Haig Sir John Jellicoe Victor Emmanuel III Luigi Cadorna Armando Diaz Woodrow... A term indicating that the state of something, which is normally open, is now totally closed. ...


Shapiro-Keyser model

A second competing theory for extratropical cyclone development over the oceans is the Shapiro-Keyser model, developed in 1990.[21] 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. 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. Fig. ... An Air France Boeing 777, a modern passenger jet. ...


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.[22] 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.[23] ERICA, or the Experiment on Rapidly Intensifying Cyclones over the Atlantic, is a scientific field project that started in the winter of 1988/1999. ... Chevron may refer to: Chevron, a V-shaped pattern seen in military or police insigna, heraldry, flag design, and architectural frets Chevron, a series of bones on the underside of the tail of reptiles Chevron Corporation, a petrochemical company Chevron Cars, an advertising campaign of the Chevron Corporation including stylized...


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 most intense warm seclusions often attain pressures less than 950 millibars (28.05 inHg) with a definitive lower to mid-level warm core structure.[22] A warm seclusion, the result of a baroclinic lifecycle, occurs at latitudes well poleward of the tropics. The process known as "tropical transition" involves the usually slow development of an extratropically cold core vortex into a tropical cyclone.[24][25] Eye of Category 4 Hurricane Isabel seen from the International Space Station on September 15, 2003 The eye is a region of mostly calm weather found at the center of strong tropical cyclones. ... Cyclone Catarina, a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004 Hurricane and Typhoon redirect here. ... Convection is the internal movement of currents within fluids (i. ...


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.[21][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 the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks. ... For other uses, see Ocean (disambiguation). ... Wind, tacuinum sanitatis casanatensis (XIV century) Wind is the rough horizontal movement of air (as opposed to an air current) caused by uneven heating of the Earths surface. ... For the singer, see Rain (singer). ...


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).[27] Hurricane Maria was the thirteenth named storm, sixth hurricane, and fourth major hurricane of the 2005 Atlantic hurricane season. ...


Motion

A zonal flow regime. Note the dominant west-to-east flow as shown in the 500 hPa height pattern.
A zonal flow regime. Note the dominant west-to-east flow as shown in the 500 hPa height pattern.

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. 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". Image File history File links Zonalflow. ... Image File history File links Zonalflow. ... A zonal flow regime. ...


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 pattern of October 23, 2003. ...


Changes in direction of this nature are most commonly observed as a result of a cylone's interaction with other low pressure systems, troughs, ridges, or with anticyclones. 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. It is also common for an extratropical cyclone to strengthen as the blocking anticyclone or ridge weakens in these circumstances.[30] A low, or a low pressure area, is a region of rising atmospheric air. ... A trough is an elongated region of relatively low atmospheric pressure, often associated with fronts. ... A ridge is an elongated region of relatively high atmospheric pressure, the opposite of a trough. ... In meteorology, an anticyclone (i. ... An example of an omega block near North America in May 2006 Blocks in meteorology are large scale patterns in the atmospheric pressure field that are nearly stationary, effectively blocking or redirecting migratory cyclones. ...


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"). 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. Vortex created by the passage of an aircraft wing, revealed by coloured smoke A vortex (pl. ... The Fujiwhara effect or Fujiwhara interaction is a type of interaction between two nearby cyclonic vortices. ...

Effects

General

Preferred region of snowfall in an extratropical cyclone
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). The band of precipitation that is associated with the warm front is often extensive. 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. 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. Image File history File links Download high-resolution version (1000x678, 77 KB) From a Central Region Snow Workshop, powerpoint presentation on CSI www. ... Image File history File links Download high-resolution version (1000x678, 77 KB) From a Central Region Snow Workshop, powerpoint presentation on CSI www. ... Wind, tacuinum sanitatis casanatensis (XIV century) Wind is the rough horizontal movement of air (as opposed to an air current) caused by uneven heating of the Earths surface. ... Kilometres per hour (American spelling: kilometers per hour) is a unit of both speed (scalar) and velocity (vector). ... Miles per hour is a unit of speed, expressing the number of international miles covered per hour. ... A European windstorm is a severe cyclonic storm that tracks across the North Atlantic towards northwestern Europe in the winter months. ... In meteorology, a weather front is a boundary between two air masses with differing characteristics (e. ... A shelf cloud associated with a heavy or severe thunderstorm over Enschede, The Netherlands. ... Thundersnow is a particularly rare meteorological phenomenon that includes the typical behavior of a thunderstorm, but with snow falling as the primary precipitation instead of rain. ... Fall redirects here. ... Winter is one of the four seasons of temperate zones. ... Spring is one of the four seasons of temperate zones, the transition from winter into summer. ... Atmosphere diagram showing the mesosphere and other layers. ...


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.[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. A trough is an elongated region of relatively low atmospheric pressure, often associated with fronts. ... This does not cite its references or sources. ... The Great Plains covers much of the central United States, portions of Canada and Mexico. ... Rockies may also refer to the National League Baseball team, the Colorado Rockies. ... The Fujita scale (F-Scale), or Fujita-Pearson scale, rates a tornados intensity by the damage it inflicts on human-built structures and sometimes on vegetation. ...


Explosive development of extratropical cyclones can be sudden. The storm known in the UK as the "Great Storm of 1987" deepened to 953 millibars (28.14 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 £1.2 billion (US$2.3 billion).[35][36] Satellite image of the powerful storm The Great Storm of 1987 occurred on October 15 and 16, 1987, when an unusually strong weather system caused hurricane force winds to hit much of the south of England. ... ISO 4217 Code GBP User(s) United Kingdom Inflation 2. ... ISO 4217 Code USD User(s) the United States, the British Indian Ocean Territory[1], the British Virgin Islands, East Timor, Ecuador, El Salvador, the Marshall Islands, Micronesia, Palau, Panama, Turks and Caicos Islands, and the insular areas of the United States Inflation 2. ...


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. 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. 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). [37] Lowest pressure ≤937 mbar (hPa)[1] Damage $381+ million (1954 USD)[2] $3–5 billion (2005 USD) Fatalities 600 – 1,200 direct Areas affected Grenada, Haiti, Bahamas, South Carolina, North Carolina, Virginia, West Virginia, Maryland, Pennsylvania, New York, Toronto and southern and eastern Ontario Part of the 1954 Atlantic hurricane... Official language(s) English Capital Raleigh Largest city Charlotte Area  Ranked 28th  - Total 53,865 sq mi (139,509 km²)  - Width 150 miles (240 km)  - Length 560[1] miles (901 km)  - % water 9. ... The Columbus Day Storm of 1962 was an extratropical wave cyclone that ranked among the most intense to strike the United States Pacific Northwest since at least 1948, and probably since the January 9, 1880, Great Gale and snowstorm. ... Official language(s) None Capital Salem Largest city Portland Area  Ranked 9th  - Total 98,466 sq mi (255,026 km²)  - Width 260 miles (420 km)  - Length 360 miles (580 km)  - % water 2. ... Official language(s) None Capital Olympia Largest city Seattle Area  Ranked 18th  - Total 71,342 sq mi (184,827 km²)  - Width 240 miles (385 km)  - Length 360 miles (580 km)  - % water 6. ... Lowest pressure 882 mbar (hPa) (Lowest pressure ever recorded in an Atlantic hurricane) Damage $28. ...


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. In the United States, the Columbus Day Storm of 1962 led to Oregon's lowest measured pressure of 965.5 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.[39] Combatants Allies: Second French Empire United Kingdom Ottoman Empire Kingdom of Sardinia Russian Empire Bulgarian volunteers Casualties 90,000 French 35,000 Turkish 17,500 British 2,050 Sardinian killed, wounded and died of disease 256,000 killed, wounded and died of disease The Crimean War (1854–1856) was fought... November 14 is the 318th day of the year (319th in leap years) in the Gregorian Calendar, with 47 days remaining. ... 1854 (MDCCCLIV) was a common year starting on Sunday (see link for calendar). ... The Columbus Day Storm of 1962 was an extratropical wave cyclone that ranked among the most intense to strike the United States Pacific Northwest since at least 1948, and probably since the January 9, 1880, Great Gale and snowstorm. ... Official language(s) None Capital Salem Largest city Portland Area  Ranked 9th  - Total 98,466 sq mi (255,026 km²)  - Width 260 miles (420 km)  - Length 360 miles (580 km)  - % water 2. ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... Vancouver Island is separated from mainland British Columbia by the Strait of Georgia and the Queen Charlotte Strait, and from Washington by the Juan De Fuca Strait. ... October 11 is the 284th day of the year (285th in leap years) in the Gregorian calendar. ...


See also

Weather Portal
Cyclones and Anticyclones of the world
v  d  e
Extratropical - Meso-scale - Polar - Polar low - Subtropical - Tropical

Image File history File links Portal. ... Radar image of a tropical cyclone in the northern hemisphere. ... In meteorology, an anticyclone (i. ... This article or section may be confusing for some readers, and should be edited to be clearer or more simplified. ... Polar cyclones (also known as Arctic Cyclones) are vast areas of low pressure. ... Polar lows are similar in behavior and size to tropical cyclones, although generally much shorter lived. ... A subtropical cyclone is a weather system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. ... Cyclone Catarina, a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004 Hurricane and Typhoon redirect here. ... Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere. ... A European windstorm is a severe cyclonic storm that tracks across the North Atlantic towards northwestern Europe in the winter months. ... Satellite image of the intense noreaster responsible for the North American blizzard of 2006. ... A surface weather analysis for the United States on October 21, 2006. ... Thundersnow is a particularly rare meteorological phenomenon that includes the typical behavior of a thunderstorm, but with snow falling as the primary precipitation instead of rain. ... A shelf cloud associated with a heavy or severe thunderstorm over Enschede, The Netherlands. ... Cyclone Catarina, a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004 Hurricane and Typhoon redirect here. ... Global Tropical Cyclone Tracks Cyclogenesis is the technical term describing the development or strengthening of a surface low pressure system, or cyclone, in the atmosphere. ...

References

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  Results from FactBites:
 
Cyclone - Wikipedia, the free encyclopedia (1047 words)
Cyclones are responsible for a wide variety of different meteorological phenomena such as tropical cyclones and tornadoes.
Extratropical cyclones (or low-pressure cells) lie somewhere in between tropical cyclones and mid-latitude cyclones, drawing a portion of their energy through the evaporation and condensation of ocean water, and some through horizontal temperature gradients in the atmosphere.
On April 27, 1999, a rare cyclone 1,100 miles in diameter was detected by the Hubble Space Telescope in the northern polar region of Mars.
Extratropical cyclone - Wikipedia, the free encyclopedia (475 words)
Extratropical cyclones lie somewhere in between tropical cyclones and mid-latitude cyclones, drawing a portion of their energy through the evaporation and condensation of ocean water, and some through horizontal temperature gradients in the atmosphere.
In an extratropical transition, poleward displacement of the cyclone occurs and the cyclone's primary energy source converts from the release of latent heat of condensation to a baroclinic process.
Extratropical cyclones are generally mild storms with surface winds of 7-15 knots.
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