Summer is the hottest of the four temperate seasons, falling after spring and before autumn. At the summer solstice, the days are longest and the nights are shortest, with day length decreasing as the season progresses after the solstice; the date of the beginning of summer varies according to climate and culture. When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere, vice versa. From an astronomical view, the equinoxes and solstices would be the middle of the respective seasons, but sometimes astronomical summer is defined as starting at the solstice, the time of maximal insolation identified with the 21st day of June or December. A variable seasonal lag means that the meteorological center of the season, based on average temperature patterns, occurs several weeks after the time of maximal insolation; the meteorological convention is to define summer as comprising the months of June and August in the northern hemisphere and the months of December and February in the southern hemisphere.
Under meteorological definitions, all seasons are arbitrarily set to start at the beginning of a calendar month and end at the end of a month. This meteorological definition of summer aligns with the viewed notion of summer as the season with the longest days of the year, in which daylight predominates; the meteorological reckoning of seasons is used in Australia, Denmark and Japan. It is used by many in the United Kingdom. In Ireland, the summer months according to the national meteorological service, Met Éireann, are June and August. However, according to the Irish Calendar, summer ends on 1 August. School textbooks in Ireland follow the cultural norm of summer commencing on 1 May rather than the meteorological definition of 1 June. Days continue to lengthen from equinox to solstice and summer days progressively shorten after the solstice, so meteorological summer encompasses the build-up to the longest day and a diminishing thereafter, with summer having many more hours of daylight than spring.
Reckoning by hours of daylight alone, summer solstice marks the midpoint, not the beginning, of the seasons. Midsummer takes place over the shortest night of the year, the summer solstice, or on a nearby date that varies with tradition. Where a seasonal lag of half a season or more is common, reckoning based on astronomical markers is shifted half a season. By this method, in North America, summer is the period from the summer solstice to the autumn equinox. Reckoning by cultural festivals, the summer season in the United States is traditionally regarded as beginning on Memorial Day weekend and ending on Labor Day, more in line with the meteorological definition for the parts of the country that have four-season weather; the similar Canadian tradition starts summer on Victoria Day one week prior and ends, as in the United States, on Labour Day. In Chinese astronomy, summer starts on or around 5 May, with the jiéqì known as lìxià, i.e. "establishment of summer", it ends on or around 6 August.
In southern and southeast Asia, where the monsoon occurs, summer is more defined as lasting from March, April and June, the warmest time of the year, ending with the onset of the monsoon rains. Because the temperature lag is shorter in the oceanic temperate southern hemisphere, most countries in this region use the meteorological definition with summer starting on 1 December and ending on the last day of February. Summer is traditionally associated with warm weather. In the Mediterranean regions, it is associated with dry weather, while in other places it is associated with rainy weather; the wet season is the main period of vegetation growth within the savanna climate regime. Where the wet season is associated with a seasonal shift in the prevailing winds, it is known as a monsoon. In the northern Atlantic Ocean, a distinct tropical cyclone season occurs from 1 June to 30 November; the statistical peak of the Atlantic hurricane season is 10 September. The Northeast Pacific Ocean has a broader period of activity, but in a similar time frame to the Atlantic.
The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and March and a peak in early September. In the North Indian basin, storms are most common from April to December, with peaks in May and November. In the Southern Hemisphere, the tropical cyclone season runs from 1 November until the end of April with peaks in mid-February to early March. Thunderstorm season in the United States and Canada runs in the spring through summer; these storms can produce hail, strong winds and tornadoes during the afternoon and evening. Schools and universities have a summer break to take advantage of the warmer weather and longer days. In all countries, children are out of school during this time of year for summer break, although dates vary. In the United States, public schools end in late May in Memorial Day weekend, while colleges finish in early May, although some schools get out on the last or second last Thursday in May. In England and Wales, school resumes again in early September.
In Canada the summer holiday starts on the last or second-last Friday in June and ends in late August or on the first Monday of September, with the exception of when that date falls before Labour Day, in which case, ends on the second Monday of the month. In Russia the summer
The levant is an easterly wind that blows in the western Mediterranean Sea and southern France, an example of mountain-gap wind. In Roussillon it is called "llevant" and in Corsica "levante". In the western Mediterranean when the wind blows through the Strait of Gibraltar, it is called the Viento de Levante or the Levanter, it is known as the Solano. When blowing moderately or the levant causes heavy swells on the Mediterranean. Gentle and damp, the levant brings clouds and rain; when it brings good weather, it is known as "levante calma" in Gibraltar. The origin of the name is the same as the origin of the Levant, the region of the eastern Mediterranean: it is the Middle French word "levant", the participle of lever "to raise" — as in soleil levant "rising sun" — from the Latin levare, it thus referred to the Eastern direction of the rising sun. The name of the wind pattern comes from the levante, the perceived origin point of the rain, it is used to describe both east and the wind coming from the east.
The opposite of the levante is the poniente. Levante refers to the fact that the sun rises from the east. In the same way, poniente comes from the verb poner and refers to the fact that the sun sets in the west. Both of these terms and poniente, are used in Spanish sea terminology to indicate directions and west, while at sea; the wind rises in the central Mediterranean or around the Balearic Islands and blows westwards reaching its greatest intensity through the Strait of Gibraltar. The winds are moist carrying fog and precipitation in the eastern side of the Strait, but dry in the western side, as the moisture rains on the mountains between Algeciras and Tarifa; the winds are well known for creating a particular cloud formation above the Rock of Gibraltar. The Levanter winds are most common from May to October; the Strait of Gibraltar, located at the western entrance to the Mediterranean Sea, is associated with strong gap winds that can produce dangerous seas when they blow against tide, current or swell through the Strait, a narrow sea-level passage about 15 km wide and 55 km long, surrounded by terrain reaching several thousand feet.
The most pronounced gap wind though the Strait, the Levanter, can produce winds of 20-40 kt in and to the west of the gap when there is higher pressure to the east, over the Mediterranean, with lower pressure to the west of Gibraltar. The sinking motions accompanying such anticyclonic conditions cause stability in the low-level air flow suppressing vertical air motion and may result in the formation of an inversion within a few thousand feet of the surface; such an inversion provides a cap that contains the low-level air and results in greater topographic blocking and the acceleration of the airflow through the gap forming the Strait. Under such circumstances, the winds can go from a moderate or fresh easterly over the Alboran Sea to gale force strength on the western side of the Strait and to its west; because the flow is accelerating and there is a significant pressure gradient through the Strait, the strongest winds are not observed mid-Strait, as might be expected if the funnel mechanism was dominant.
Levanters are most frequent during the warm season from April until October and reach a peak in spring, when the Mediterranean is comparatively cool, increasing the stability of the low-level air flow. Sometimes the levanter forms a characteristic cloud over the Rock of Gibraltar. However, this is not always the case and a particular set of conditions is required for its formation. Near the surface, the levanter is unsaturated; as the moist air, which must be capped to be stable and so unable to rise by convection, is forced to rise over the Rock, the moisture condenses to form a cloud which streams away west from its top. If wind speeds are too low and stability high in the near-surface layer, the cloud does not form and condensation is sensitive to small changes in moisture content, such that when the wind across the Rock veers into the southeast, the flow becomes too dry for the cloud to form, bringing drier air from North Africa; when the wind speed is too low, the air is unable to rise to form the cloud.
At high wind speeds, the turbulent mixing to the lee of the Rock distributes the moisture through a comparatively deep layer and the cloud is, at best broken. It dissolves west of the Rock in these turbulent windy conditions. In suitable conditions, the characteristic "pennant" cloud, it extends about 5 km west from the top of the Rock in a turbulent plume. This cloud hangs over the centre of the city of Gibraltar, while there is sunny weather in to the north and south from the southern outskirts of the city. On the western side of the Rock, the winds near sea level are from the west or southwest, as the air forms large overturning rolls, more than 350 m deep in the lee protection of the mountain, but strong winds tend to alter this flow regime, as described in #Strong winds across the Rock; the pennant
The mistral is a strong, northwesterly wind that blows from southern France into the Gulf of Lion in the northern Mediterranean. It produces sustained winds exceeding 66 km/h, sometimes reaching 185 km/h, it is most common in the winter and spring, strongest in the transition between the two seasons. Periods of the wind exceeding 30 km/h for more than sixty-five hours have been reported. In France, it refers to a violent, north or northwest wind that accelerates when it passes through the valleys of the Rhône and the Durance Rivers to the coast of the Mediterranean around the Camargue region, it affects the northeast of the plain of Languedoc and Provence to the east of Toulon, where it is felt as a strong west wind. It has a major influence all along the Mediterranean coast of France, causes sudden storms in the Mediterranean between Corsica and the Balearic Islands; the name mistral comes from the Languedoc dialect of the Occitan and means "masterly". The same wind is called mistrau in the Provençal variant of Occitan, mestral in Catalan, maestrale in Italian and Corsican, maistràle or bentu maestru in Sardinian, majjistral in Maltese.
The mistral is accompanied by clear, fresh weather, it plays an important role in creating the climate of Provence. It can reach speeds of more than 90 km/h in the Rhône Valley, its average speed during the day can reach about 50 km/h, calming noticeably at night. The mistral blows in winter or spring, though it occurs in all seasons, it sometimes lasts only one or two days lasts several days, sometimes lasts more than a week. The mistral takes place each time there is an anticyclone, or area of high pressure, in the Bay of Biscay, an area of low pressure around the Gulf of Genoa; when this happens, the flow of air between the high and low pressure areas draws in a current of cold air from the north which accelerates through the lower elevations between the foothills of the Alps and the Cevennes. The conditions for a mistral are more favorable when a cold rainy front has crossed France from the northwest to the southeast as far as the Mediterranean; this cold, dry wind causes a period of cloudless skies and luminous sunshine, which gives the mistral its reputation for making the sky clear.
There is however, the mistral noir, which brings clouds and rain. The mistral noir occurs when the Azores High is extended and draws in unusually moist air from the northwest; the long and enclosed shape of the Rhône Valley, the Venturi effect of funnelling the air through a narrowing space, is cited as the reason for the speed and force of the mistral, but the reasons are more complex. The mistral reaches its maximum speed not at the narrowest part of the Rhône Valley, south of Valence, but much farther south, where the Valley has widened; the wind occurs not just in the Valley, but high above in the atmosphere, up to the troposphere, 3 km above the earth. The mistral is strong at the summit of Mont Ventoux, 1900 meters in elevation, though the plain below is wide. Other contributing factors to the strength of the mistral are the accumulation of masses of cold air, whose volume is greater, pouring down the mountains and valleys to the lower elevations; this is similar to a foehn wind, but unlike a foehn wind the descent in altitude does not warm the mistral.
The causes and characteristics of the mistral are similar to those of the Tramontane, another wind of the French Mediterranean region. In France, the mistral affects Provence, Languedoc east of Montpellier, as well as all of the Rhône Valley from Lyon to Marseille, as far southeast as Corsica and Sardinia; the mistral blows from the north or northwest, but in certain pre-alpine valleys and along the Côte d'Azur, the wind is channelled by the mountains so that it blows from east to west. Sometimes it blows from the north-north-east toward the east of Languedoc as far as Cap Béar; the mistral will affect only one part of the region. In the Languedoc area, where the tramontane is the strongest wind, the mistral and the tramontane blow together onto the Gulf of Lion and the northwest of the western Mediterranean, can be felt to the east of the Balearic Islands, in Sardinia, sometimes as far as the coast of Africa; when the mistral blows from the west, the mass of air is not so cold and the wind only affects the plain of the Rhône delta and the Côte d'Azur.
The good weather is confined to the coast of the Mediterranean. The Côte d'Azur has a clear sky and warmer temperatures; this type of mistral blows for no more than one to three days. The mistral originating from the northeast has a different character. In the winter this is by far the coldest form of the mistral; the wind can blow for more than a week. This kind of mistral is connected with a low pressure area in the Gulf of Genoa, it can bring unstable weather to the Côte d'Azur and the east of Provence, sometimes bringing heavy snow to low altitudes in winter; when the flow of air comes from the northeast due to a widespread low pressure area over the Atlantic and atmospheric disturbances over France, the air is colder at both high altitudes and ground level, the mistral is stronger, the weather worse, with the creation of cumulus clouds bringing weak storms. This kind of mistral is weaker in the east of the Côte d'Azur; the mistral is not alw
A supercell is a thunderstorm characterized by the presence of a mesocyclone: a deep, persistently rotating updraft. For this reason, these storms are sometimes referred to as rotating thunderstorms. Of the four classifications of thunderstorms, supercells are the overall least common and have the potential to be the most severe. Supercells are isolated from other thunderstorms, can dominate the local weather up to 32 kilometres away, they tend to last 2-4 hours. Supercells are put into three classification types: Classic, Low-precipitation, High-precipitation. LP supercells are found in climates that are more arid, such as the high plains of the United States, HP supercells are most found in moist climates. Supercells can occur anywhere in the world under the right pre-existing weather conditions, but they are most common in the Great Plains of the United States in an area known as Tornado Alley and in the Tornado Corridor of Argentina and southern Brazil. Supercells are found isolated from other thunderstorms, although they can sometimes be embedded in a squall line.
Supercells are found in the warm sector of a low pressure system propagating in a north easterly direction in line with the cold front of the low pressure system. Because they can last for hours, they are known as quasi-steady-state storms. Supercells have the capability to deviate from the mean wind. If they track to the right or left of the mean wind, they are said to be "right-movers" or "left-movers," respectively. Supercells can sometimes develop two separate updrafts with opposing rotations, which splits the storm into two supercells: one left-mover and one right-mover. Supercells can be any size – large or small, low or high topped, they produce copious amounts of hail, torrential rainfall, strong winds, substantial downbursts. Supercells are one of the few types of clouds that spawn tornadoes within the mesocyclone, although only 30% or fewer do so. Supercells can occur anywhere in the world under the right weather conditions; the first storm to be identified as the supercell type was the Wokingham storm over England, studied by Keith Browning and Frank Ludlam in 1962.
Browning did the initial work, followed up by Lemon and Doswell to develop the modern conceptual model of the supercell. To the extent that records are available, supercells are most frequent in the Great Plains of the central United States and southern Canada extending into the southeastern U. S. and northern Mexico. Supercells occur in many other mid-latitude regions, including Eastern China and throughout Europe; the areas with highest frequencies of supercells are similar to those with the most occurrences of tornadoes. The current conceptual model of a supercell was described in Severe Thunderstorm Evolution and Mesocyclone Structure as Related to Tornadogenesis by Leslie R. Lemon and Charles A. Doswell III.. Supercells derive their rotation through tilting of horizontal vorticity caused by wind shear. Strong updrafts lift the air turning about a horizontal axis and cause this air to turn about a vertical axis; this forms the mesocyclone. A cap or capping inversion is required to form an updraft of sufficient strength.
The cap puts an inverted layer above a normal boundary layer, by preventing warm surface air from rising, allows one or both of the following: Air below the cap warms and/or becomes more moist Air above the cap coolsThis creates a warmer, moister layer below a cooler layer, unstable. When the cap weakens or moves, explosive development follows. In North America, supercells show up on Doppler radar as starting at a point or hook shape on the southwestern side, fanning out to the northeast; the heaviest precipitation is on the southwest side, ending abruptly short of the rain-free updraft base or main updraft. The rear flank downdraft, or RFD, carries precipitation counterclockwise around the north and northwest side of the updraft base, producing a "hook echo" that indicates the presence of a mesocyclone; this "dome" feature appears above the strongest updraft location on the anvil of the storm. It is a result of a powerful updraft. An observer, at ground level too close to the storm is unable to see the overshooting top due to the fact that the anvil blocks the sight of this feature.
The overshooting is visible from satellite images as a "bubbling" amidst the otherwise smooth upper surface of the anvil cloud. An anvil forms when the storm's updraft collides with the upper levels of the lowest layer of the atmosphere, or the tropopause, has nowhere else to go due to the laws of fluid dynamics- pressure and density; the anvil is cold and precipitation free though virga can be seen falling from the forward sheared anvil. Since there is so little moisture in the anvil, winds can move freely; the clouds take on their anvil shape when the rising air reaches 15,200 -- more. The anvil's distinguishing feature is. In some cases, it can shear backwards, called a backsheared anvil, another sign of a strong updraft; this area on the southern side of the storm in North America
European windstorms are the strongest extratropical cyclones which occur across the continent of Europe. They form as cyclonic windstorms associated with areas of low atmospheric pressure, they are most common in the winter months. On average, the month when most windstorms form is January; the seasonal average is 4.6 windstorms. Deep low pressure areas are common over the North Atlantic, sometimes starting as nor'easters off the New England coast, track across the North Atlantic Ocean towards western Europe, past the north coast of Great Britain and Ireland and into the Norwegian Sea. However, when they track further south, they can affect any country in Europe. Affected countries include the United Kingdom, the Netherlands, the Faroe Islands and Iceland, but any country in Central Europe, Northern Europe and Western Europe is struck by such a storm system. On average, these storms cause economic damage of around €1.9 billion per year, insurance losses of €1.4 billion per year. They rank as the second highest cause of global natural catastrophe insurance loss, after U.
S. hurricanes. Up to the second half of the 19th century, European windstorms were named after the person who spotted them, they would be named either by the year, the date, the Saint's day of their occurrence or any other way that made them known. However, a storm may still be named differently in different countries. For instance, the Norwegian weather service names independently notable storms that affect Norway, which can result in multiple names being used in different countries they affect, such as: 1999 storm "Anatol" in Germany, is known as the "December hurricane" or "Adam" in Denmark and as "Carola" in Sweden. 2011 storm "Dagmar" in Norway and Sweden is known as "Tapani" in Finland. 2013 St. Jude storm in the English media, is known as Christian in German and French it was named Simone by the Swedish Meteorological and Hydrological Institute, as the October storm in Danish and Dutch, it was given the name Allan by the Danish Meteorological Institute following the political decision to name strong storms which affect Denmark.
An alternative Scottish naming system arose in 2011 via social media/Twitter which resulted in the humorous naming of Hurricane Bawbag and Hurricane Fannybaws. Such usage of the term Hurricane is not without precedent, as the 1968 Scotland storm was referred to as "Hurricane Low Q"; the UK Met Office and Ireland's Met Éireann held discussions about developing a common naming system for Atlantic storms. In 2015 a pilot project by the two forecasters was launched as "Name our storms" which sought public participation in naming large-scale cyclonic windstorms affecting the UK and/or Ireland over the winter of 2015/16; the UK/Ireland storm naming system began its first operational season in 2017/2018. An independent forecaster, the European Windstorm Centre has its own naming list, although this is not an official list. During 1954, Karla Wege, a student at the Free University of Berlin's meteorological institute suggested that names should be assigned to all areas of low and high pressure that influenced the weather of Central Europe.
The university subsequently started to name every area of high or low pressure within its weather forecasts, from a list of 260 male and 260 female names submitted by its students. The female names were assigned to areas of low pressure while male names were assigned to areas of high pressure; the names were subsequently used by Berlin's media until February 1990, after which the German media started to use the names, they were not approved by the German Meteorological Service Deutscher Wetterdienst. The DWD subsequently banned the usage of the names by their offices during July 1991, after complaints had poured in about the naming system. However, the order was leaked to the German press agency, Deutsche Presse-Agentur, who ran it as its lead weather story. Germany's ZDF television channel subsequently ran a phone in poll on 17 July 1991 and claimed that 72% of the 40,000 responses favored keeping the names; this made the DWD pause and think about the naming system and these days the DWD accept the naming system and request that it is maintained.
During 1998 a debate started about if it was discrimination to name areas of high pressure with male names and the areas of low pressure with female names. The issue was subsequently resolved by alternating male and female names each year. In November 2002 the "Adopt-a-Vortex" scheme began, which allows members of the public or companies to buy naming rights for a letter chosen by the buyer that are assigned alphabetically to high and low pressure areas in Europe during each year; the naming comes with the slim chance. The money raised by this is used by the meteorology department to maintain weather observations at the Free University. Several European languages use cognates of the word huracán to indicate strong cyclonic winds occurring in Europe; the term hurricane as applied to these storms is not in reference to the structurally different tropical cyclone of the same name, but to the hurricane strength of the wind on the Beaufort scale. In English, use of term hurricane to refer to European windstorms is discouraged, as these storms do not display the structure of tropical storms.
The use of the French term ouragan is discouraged as hurricane is in English, as it is reserved for tropical storms
Spring is one of the four temperate seasons, following winter and preceding summer. There are various technical definitions of spring, but local usage of the term varies according to local climate and customs; when it is spring in the Northern Hemisphere, it is autumn in the Southern Hemisphere and vice versa. At the spring equinox and nights are twelve hours long, with day length increasing and night length decreasing as the season progresses. Spring and "springtime" refer to the season, to ideas of rebirth, renewal and regrowth. Subtropical and tropical areas have climates better described in terms of other seasons, e.g. dry or wet, monsoonal or cyclonic. Cultures may have local names for seasons which have little equivalence to the terms originating in Europe. Meteorologists define four seasons in many climatic areas: spring, summer and winter; these are demarcated by the values of their average temperatures on a monthly basis, with each season lasting three months. The three warmest months are by definition summer, the three coldest months are winter and the intervening gaps are spring and autumn.
Spring, when defined in this manner, can start on different dates in different regions. Thus, in the US and UK, spring months are March and May, while in New Zealand and Australia, spring conventionally begins on September 1 and ends November 30. Swedish meteorologists define the beginning of spring as the first occasion on which the average daytime temperature exceeds zero degrees Celsius for seven consecutive days, thus the date varies with latitude and elevation. In some cultures in the Northern Hemisphere, the astronomical vernal equinox is taken to mark the first day of spring, the summer solstice is taken as the first day of summer. In Persian culture the first day of spring is the first day of the first month which begins on 20 or 21 March. In other traditions, the equinox is taken as mid-spring. In the traditional Chinese calendar, the "spring" season consists of the days between Lichun, taking Chunfen as its midpoint ending at Lixia. According to the Celtic tradition, based on daylight and the strength of the noon sun, spring begins in early February and continues until early May.
The beginning of spring is not always determined by fixed calendar dates. The phenological or ecological definition of spring relates to biological indicators, such as the blossoming of a range of plant species, the activities of animals, the special smell of soil that has reached the temperature for micro flora to flourish; these indicators, along with the beginning of spring, vary according to the local climate and according to the specific weather of a particular year. Most ecologists divide the year into six seasons. In addition to spring, ecological reckoning identifies an earlier separate prevernal season between the hibernal and vernal seasons; this is a time when only the hardiest flowers like the crocus are in bloom, sometimes while there is still some snowcover on the ground. During early spring, the axis of the Earth is increasing its tilt relative to the Sun, the length of daylight increases for the relevant hemisphere; the hemisphere begins to warm causing new plant growth to "spring forth," giving the season its name.
Any snow begins to melt, swelling streams with runoff and any frosts become less severe. In climates that have no snow, rare frosts and ground temperatures increase more rapidly. Many flowering plants bloom at this time of year, in a long succession, sometimes beginning when snow is still on the ground and continuing into early summer. In snowless areas, "spring" may begin as early as February or August, heralded by the blooming of deciduous magnolias and quince. Many temperate areas have a dry spring, wet autumn, which brings about flowering in this season, more consistent with the need for water, as well as warmth. Subarctic areas may not experience "spring" at all until May. While spring is a result of the warmth caused by the changing orientation of the Earth's axis relative to the Sun, the weather in many parts of the world is affected by other, less predictable events; the rainfall in spring follows trends more related to longer cycles—such as the solar cycle—or events created by ocean currents and ocean temperatures—for example, the El Niño effect and the Southern Oscillation Index.
Unstable spring weather may occur more when warm air begins to invade from lower latitudes, while cold air is still pushing from the Polar regions. Flooding is most common in and near mountainous areas during this time of year, because of snow-melt, accelerated by warm rains. In North America, Tornado Alley is most active at this time of year since the Rocky Mountains prevent the surging hot and cold air masses from spreading eastward, instead force them into direct conflict. Besides tornadoes, supercell thunderstorms can produce dangerously large hail and high winds, for which a severe thunderstorm warning or tornado warning is issued. More so than in winter, the jet streams play an important role in unstable and severe Northern Hemisphere weather in springtime. In recent decades, season creep has been observed, which means that many phenological signs of spring are occurring earlier in many regions by around two days per decade. Spring in the Southern Hemisphere is different in several significant ways to that of the Northern Hemisphere
A storm is any disturbed state of an environment or in an astronomical body's atmosphere affecting its surface, implying severe weather. It may be marked by significant disruptions to normal conditions such as strong wind, hail and lightning, heavy precipitation, heavy freezing rain, strong winds, or wind transporting some substance through the atmosphere as in a dust storm, sandstorm, etc. Storms have the potential to harm lives and property via storm surge, heavy rain or snow causing flooding or road impassibility, lightning and vertical wind shear. Systems with significant rainfall and duration help alleviate drought in places. Heavy snowfall can allow special recreational activities to take place which would not be possible otherwise, such as skiing and snowmobiling; the English word comes from Proto-Germanic *sturmaz meaning "noise, tumult". Storms are created when a center of low pressure develops with the system of high pressure surrounding it; this combination of opposing forces can create winds and result in the formation of storm clouds such as cumulonimbus.
Small localized areas of low pressure can form from hot air rising off hot ground, resulting in smaller disturbances such as dust devils and whirlwinds. There are many varieties and names for storms: Blizzard — There are varying definitions for blizzards, both over time and by location. In general, a blizzard is accompanied by gale-force winds, heavy snow, cold conditions; the temperature criterion has fallen out of the definition across the United States Bomb cyclone - A rapid deepening of a mid-latitude cyclonic low-pressure area occurring over the ocean, but can occur over land. The winds experienced during these storms can be as powerful as that of a hurricane. Coastal Storm — large wind waves and/or storm surge that strike the coastal zone, their impacts include coastal erosion and coastal flooding Derecho — A derecho is a widespread, long-lived, straight-line wind storm, associated with a land-based, fast-moving group of severe thunderstorms. Dust devil — a small, localized updraft of rising air.
Dust storm - A situation in which winds pick up large quantities of sand or soil reducing the visibility Firestorm — Firestorms are conflagrations which attain such intensity that they create and sustain their own wind systems. It is most a natural phenomenon, created during some of the largest bushfires, forest fires, wildfires; the Peshtigo Fire is one example of a firestorm. Firestorms can be deliberate effects of targeted explosives such as occurred as a result of the aerial bombings of Dresden. Nuclear detonations generate firestorms. Gale — An extratropical storm with sustained winds between 34–48 knots. Hailstorm — a type of storm that precipitates round chunks of ice. Hailstorms occur during regular thunderstorms. While most of the hail that precipitates from the clouds is small and harmless, there are occasional occurrences of hail greater than 2 inches in diameter that can cause much damage and injuries. Hypercane -a hypothetical tropical cyclone that could form over 50 °C water; such a storm would produce winds of over 800 km/h.
A series of hypercanes may have formed during the astroid or comet impact that killed the non-avian dinosaurs 66 million years ago. Such a phenomenon could occur during a supervolcanic eruption, or extreme global warming. Ice storm — Ice storms are one of the most dangerous forms of winter storms; when surface temperatures are below freezing, but a thick layer of above-freezing air remains aloft, rain can fall into the freezing layer and freeze upon impact into a glaze of ice. In general, 8 millimetres of accumulation is all, required in combination with breezy conditions, to start downing power lines as well as tree limbs. Ice storms make unheated road surfaces too slick to drive upon. Ice storms can vary in time range from hours to days and can cripple small towns and large metropolitan cities alike. Microburst - a powerful windstorm produced during a thunderstorm that only lasts a few minutes. Ocean Storm or sea storm — Storm conditions out at sea are defined as having sustained winds of 48 knots or greater.
Just referred to as a storm, these systems can sink vessels of all types and sizes. Snowstorm — A heavy fall of snow accumulating at a rate of more than 5 centimeters per hour that lasts several hours. Snow storms ones with a high liquid equivalent and breezy conditions, can down tree limbs, cut off power connections and paralyze travel over large regions. Squall — sudden onset of wind increase of at least 16 knots or greater sustained for at least one minute. Thunderstorm -- A thunderstorm is a type of storm that generates both thunder, it is accompanied by heavy precipitation. Thunderstorms occur throughout the world, with the highest frequency in tropical rainforest regions where there are conditions of high humidity and temperature along with atmospheric instability; these storms occur when high levels of condensation form in a volume of unstable air that generates deep, upward motion in the atmosphere. The heat energy creates powerful rising air currents. Cool descending air currents produce strong downdraughts below the storm.
After the storm has spent its energy, the rising currents die away and downdraughts break up the cloud. Individual s