Hail is a form of solid precipitation. It is distinct from ice pellets, though the two are often confused and it consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets falls generally in cold weather while hail growth is inhibited during cold surface temperatures. Unlike graupel, which is made of rime, and ice pellets, the METAR reporting code for hail 5 mm or greater is GR, while smaller hailstones and graupel are coded GS. Hail is possible within most thunderstorms as it is produced by cumulonimbus, Hail formation requires environments of strong, upward motion of air with the parent thunderstorm and lowered heights of the freezing level. In the mid-latitudes, hail forms near the interiors of continents, while in the tropics, there are methods available to detect hail-producing thunderstorms using weather satellites and weather radar imagery. Severe weather warnings are issued for hail when the stones reach a size, as it can cause serious damage to human-made structures and, most commonly.
Any thunderstorm which produces hail that reaches the ground is known as a hailstorm, Hail has a diameter of 5 millimetres or more. Hailstones can grow to 15 centimetres and weigh more than 0.5 kilograms, unlike ice pellets, hailstones are layered and can be irregular and clumped together. Although the diameter of hail is varied, in the United States, stones larger than 2 cm are usually considered large enough to cause damage. The Meteorological Service of Canada issues severe thunderstorm warnings when hail that size or above is expected, the US National Weather Service has a 2.5 cm or greater in diameter threshold, effective January 2010, an increase over the previous threshold of ¾-inch hail. Other countries have different thresholds according local sensitivity to hail, for grape growing areas could be adversely impacted by smaller hailstones. Hailstones can be large or very small, depending on how strong the updraft is. These types of strong updrafts can indicate the presence of a tornado, the growth rate is maximized where air is near a temperature of −13 °C.
Like other precipitation in clouds, hail begins as water droplets. As the droplets rise and the temperature goes below freezing, they become supercooled water, a cross-section through a large hailstone shows an onion-like structure. This means the hailstone is made of thick and translucent layers, alternating layers that are thin, white. Former theory suggested that hailstones were subjected to multiple descents and ascents, falling into a zone of humidity and this up and down motion was thought to be responsible for the successive layers of the hailstone
A subtropical cyclone is a weather system that has some characteristics of a tropical and an extratropical cyclone. As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical or extratropical cyclones and they were officially recognized by the National Hurricane Center in 1972. Subtropical cyclones began to receive names from the tropical cyclone lists in the North Atlantic, South-west Indian Ocean. There are two currently used for subtropical cyclones. Across the north Atlantic and southwest Indian Ocean, they require central convection fairly near the center, across the eastern half of the northern Pacific, they require a mid-tropospheric cyclone to cut off from the main belt of the westerlies and only a weak surface circulation. Subtropical cyclones have broad wind patterns with maximum sustained winds located farther from the center than typical tropical cyclones and this means that subtropical cyclones are more likely to form outside the traditional bounds of the North Atlantic hurricane season.
Subtropical cyclones are observed to form in the South Atlantic. Throughout the 1950s and 1960s, the term semi-tropical and quasi-tropical were used for what would become known as subtropical cyclones, the term subtropical cyclone merely referred to any cyclone located in the subtropical belt near and just north of the horse latitudes. Intense debate ensued in the late 1960s, after a number of hybrid cyclones formed in the Atlantic Basin, in 1972, the National Hurricane Center finally designated these storms as subtropical cyclones in real-time, and updated the hurricane database to include subtropical cyclones from 1968 through 1971. This name was not noted as controversial in contemporary news reports, in the North Atlantic basin, subtropical cyclones were initially named from the NATO phonetic alphabet list in the early to mid-1970s. In the intervening years of 1975–2001, subtropical storms were named from the traditional list and considered tropical in real-time. Between 1992 and 2001, two different numbers were given to subtropical depressions or subtropical storms, one for public use, for example, Hurricane Karen in 2001 was initially known as Subtropical Storm One as well as AL1301.
In 2002, the NHC began giving numbers to subtropical depressions, from 2002 onwards, Subtropical Depression 13L would be known as Subtropical Depression Thirteen instead. Hurricane Gustav of 2002 was the first Subtropical Storm to receive a name but became tropical shortly after naming, Subtropical Storm Nicole, from the 2004 Atlantic hurricane season was the first subtropical storm that did not become tropical since the policy change. A subtropical storm from the 2005 Atlantic hurricane season did not become tropical, in the southern Indian Ocean, subtropical cyclones are named once winds reach tropical storm, or gale, force. Since 2011, subtropical storms in the South Atlantic Ocean are named by the Brazilian Navy Hydrographic Center, Subtropical cyclones form in a wide band of latitude, mainly south of the 50th parallel in the northern hemisphere. In the case of the north Indian Ocean, the formation of type of vortex leads to the onset of monsoon rains during the wet season. In the southern hemisphere, subtropical cyclones are observed across southern portions of the Mozambique Channel
Extratropical cyclones are capable of producing anything from cloudiness and mild showers to heavy gales, thunderstorms and tornadoes. These types of cyclones are defined as large scale low pressure systems that occur in the middle latitudes of the Earth. In contrast with tropical cyclones, extratropical cyclones produce rapid changes in temperature and dew point along broad lines, called weather fronts, the term cyclone applies to numerous types of low pressure areas, one of which is the extratropical cyclone. The descriptor extratropical signifies that this type of cyclone generally occurs outside the tropics and they are termed mid-latitude cyclones if they form within those latitudes, or post-tropical cyclones if a tropical cyclone has intruded into the mid latitudes. Weather forecasters and the public often describe them simply as depressions or lows. Terms like frontal cyclone, frontal depression, frontal low, extratropical low, non-tropical low, Extratropical cyclones are classified mainly as baroclinic, because they form along zones of temperature and dewpoint gradient known as frontal zones.
They can become barotropic late in their cycle, when the distribution of heat around the cyclone becomes fairly uniform with its radius. Extratropical cyclones form anywhere within the regions of the Earth. 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, a separate study in the Northern Hemisphere suggests that approximately 234 significant extratropical cyclones form each winter. Extratropical cyclones form along linear bands of temperature/dewpoint gradient with significant vertical wind shear, 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. The favorable quadrants are usually at the rear and left front quadrants. The divergence causes air to rush out from the top of the air column and this in turn forces convergence in the low-level wind field and increased upward motion within the column.
The increased upward motion causes atmospheric pressure at ground level to lower and this is because the upward air motion counteracts gravity, lessening the weight of the atmosphere in that location. The lowered pressure strengthens 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 air ahead of the system is denser. Later, the cyclones occlude as the portion of the cold front overtakes a section of the warm front, forcing a tongue, or trowal. Eventually, the cyclone will become cold and begin to weaken. Atmospheric pressure can fall very rapidly when there are upper level forces on the system
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the lowest level of the atmosphere, Weather refers to day-to-day temperature and precipitation activity, whereas climate is the term for the averaging of atmospheric conditions over longer periods of time. When used without qualification, weather is understood to mean the weather of Earth. Weather is driven by air pressure and moisture differences between one place and another and these differences can occur due to the suns angle at any particular spot, which varies with latitude. The strong temperature contrast between polar and tropical air gives rise to the largest scale atmospheric circulations, the Hadley Cell, the Ferrel Cell, the Polar Cell, Weather systems in the mid-latitudes, such as extratropical cyclones, are caused by instabilities of the jet stream flow. Because the Earths axis is tilted relative to its orbital plane, on Earths surface, temperatures usually range ±40 °C annually.
Over thousands of years, changes in Earths orbit can affect the amount and distribution of energy received by the Earth, thus influencing long-term climate. Surface temperature differences in turn cause pressure differences, higher altitudes are cooler than lower altitudes as most atmospheric heating is due to contact with the Earths surface while radiative losses to space are mostly constant. Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location. The Earths weather system is a system, as a result. Human attempts to control the weather have occurred throughout history, and there is evidence that human activities such as agriculture, studying how the weather works on other planets has been helpful in understanding how weather works on Earth. A famous landmark in the Solar System, Jupiters Great Red Spot, is a storm known to have existed for at least 300 years. However, weather is not limited to planetary bodies, a stars corona is constantly being lost to space, creating what is essentially a very thin atmosphere throughout the Solar System.
The movement of mass ejected from the Sun is known as the solar wind, on Earth, the common weather phenomena include wind, rain, snow and dust storms. Less common events include natural disasters such as tornadoes, typhoons, almost all familiar weather phenomena occur in the troposphere. Weather does occur in the stratosphere and can affect weather lower down in the troposphere, Weather occurs primarily due to air pressure and moisture differences between one place to another. These differences can occur due to the sun angle at any particular spot, in other words, the farther from the tropics one lies, the lower the sun angle is, which causes those locations to be cooler due the spread of the sunlight over a greater surface. The strong temperature contrast between polar and tropical air gives rise to the large scale atmospheric circulation cells and the jet stream, Weather systems in the mid-latitudes, such as extratropical cyclones, are caused by instabilities of the jet stream flow
Autumn, known as fall in North American English, is one of the four temperate seasons. One of its features is the shedding of leaves from deciduous trees. Some cultures regard the autumnal equinox as mid-autumn, while others with a longer temperature lag treat it as the start of autumn. Meteorologists use a definition based on months, with autumn being September and November in the northern hemisphere, in North America, autumn is usually considered to start with the September equinox and end with the winter solstice. As daytime and nighttime temperatures decrease, trees shed their leaves, in traditional East Asian solar term, autumn starts on or around 8 August and ends on or about 7 November. In Ireland, the autumn months according to the meteorological service. In Australia and New Zealand, autumn officially begins on 1 March, the word autumn comes from the ancient Etruscan root autu- and has within it connotations of the passing of the year. It was borrowed by the neighbouring Romans, and became the Latin word autumnus, after the Roman era, the word continued to be used as the Old French word autompne or autumpne in Middle English, and was normalized to the original Latin.
In the Medieval period, there are examples of its use as early as the 12th century. Before the 16th century, harvest was the usually used to refer to the season. The alternative word fall for the season traces its origins to old Germanic languages, the exact derivation is unclear, with the Old English fiæll or feallan and the Old Norse fall all being possible candidates. However, these all have the meaning to fall from a height and are clearly derived either from a common root or from each other. The term came to denote the season in 16th century England, during the 17th century, English emigration to the British colonies in North America was at its peak, and the new settlers took the English language with them. While the term gradually became obsolete in Britain, it became the more common term in North America. The name backend, a common name for the season in Northern England, has today been largely replaced by the name autumn. Association with the transition from warm to cold weather, and its status as the season of the primary harvest, has dominated its themes.
In Western cultures, personifications of autumn are usually pretty, well-fed females adorned with fruits, many cultures feature autumnal harvest festivals, often the most important on their calendars. There are the many North American Indian festivals tied to harvest of ripe foods gathered in the wild, the Chinese Mid-Autumn or Moon festival, and many others
Lightning is a sudden electrostatic discharge that occurs during a thunder storm. This discharge occurs between electrically charged regions of a cloud, between two clouds, or between a cloud and the ground. The charged regions in the atmosphere temporarily equalize themselves through this discharge referred to as an if it hits an object on the ground. Lightning causes light in the form of plasma, and sound in the form of thunder, Lightning may be seen and not heard when it occurs at a distance too great for the sound to carry as far as the light from the strike or flash. This article incorporates public domain material from the National Oceanic and Atmospheric Administration document Understanding Lightning, the details of the charging process are still being studied by scientists, but there is general agreement on some of the basic concepts of thunderstorm electrification. The main charging area in a thunderstorm occurs in the part of the storm where air is moving upward rapidly and temperatures range from -15 to -25 Celsius.
At that place, the combination of temperature and rapid upward air movement produces a mixture of super-cooled cloud droplets, small ice crystals, the updraft carries the super-cooled cloud droplets and very small ice crystals upward. At the same time, the graupel, which is larger and denser. The differences in the movement of the precipitation cause collisions to occur, when the rising ice crystals collide with graupel, the ice crystals become positively charged and the graupel becomes negatively charged. The updraft carries the positively charged ice crystals upward toward the top of the storm cloud, the larger and denser graupel is either suspended in the middle of the thunderstorm cloud or falls toward the lower part of the storm. The result is that the part of the thunderstorm cloud becomes positively charged while the middle to lower part of the thunderstorm cloud becomes negatively charged. This part of the cloud is called the anvil. While this is the charging process for the thunderstorm cloud.
In addition, there is a small but important positive charge buildup near the bottom of the cloud due to the precipitation. Many factors affect the frequency, distribution and physical properties of a lightning flash in a particular region of the world. These factors include ground elevation, prevailing wind currents, relative humidity, proximity to warm and cold bodies of water, to a certain degree, the ratio between IC, CC and CG lightning may vary by season in middle latitudes. Lightnings relative unpredictability limits a complete explanation of how or why it occurs, the actual discharge is the final stage of a very complex process. At its peak, a thunderstorm produces three or more strikes to the Earth per minute
Summer is the hottest of the four temperate seasons, falling between spring and autumn. At the summer solstice, the days are longest and the nights are shortest, 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, a variable seasonal lag means that the meteorological center of the season, which is based on average temperature patterns, occurs several weeks after the time of maximal insolation. Under meteorological definitions, all seasons are set to start at the beginning of a calendar month. This meteorological definition of summer aligns with the commonly viewed notion of summer as the season with the longest days of the year, the meteorological reckoning of seasons is used in Australia, Denmark, the former Soviet Union 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 begins on 1 May, school textbooks in Ireland follow the cultural norm of summer commencing on 1 May rather than the meteorological definition of 1 June. Reckoning by hours of daylight alone, summer solstice marks the midpoint, not the beginning, midsummer takes place over the shortest night of the year, which is the summer solstice, or on a nearby date that varies with tradition. Where a seasonal lag of half a season or more is common, by this method, in North America, summer is the period from the summer solstice to the autumn equinox. 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 known as lìxià, i. e. establishment of summer. In Australia and New Zealand, summer begins on 1 December. Summer is traditionally associated with hot or 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 period of vegetation growth within the savanna climate regime. Where the wet season is associated with a shift in the prevailing winds. In the northern Atlantic Ocean, a 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, in the North Indian basin, storms are most common from April to December, with peaks in May and November
A dust devil is a strong, well-formed, and relatively long-lived whirlwind, ranging from small to large. The primary vertical motion is upward, Dust devils are usually harmless, but can on rare occasions grow large enough to pose a threat to both people and property. They are comparable to tornadoes in both are a weather phenomenon of a vertically oriented rotating column of wind. Most tornadoes are associated with a larger parent circulation, the mesocyclone on the back of a supercell thunderstorm, Dust devils form as a swirling updraft under sunny conditions during fair weather, rarely coming close to the intensity of a tornado. In the southwestern United States, a dust devil is called a dancing devil. In Death Valley, California, it may be called an auger or a dust whirl. The Navajo refer to them as chiindii, ghosts or spirits of dead Navajos, if a chindi spins clockwise, it is said to be a good spirit, if it spins counterclockwise, it is said to be a bad spirit. The Australian English term willy-willy or whirly-whirly is thought to derive from Yindjibarndi or a neighbouring language, in Aboriginal myths, willy-willies represent spirit forms.
They are often quite scary spirits, and parents may warn their children if they misbehave. There is a story of the origin of the brolga in which a bad spirit descends from the sky and captures the young being, in Saudi Arabia, Kuwait and Jordan, they often reach hundreds of meters in height and are referred to as djin. Egypt has its fasset el afreet, or ghosts wind, in Iran, this kind of wind is usually called Gerd Baad, or round wind. Among the Kikuyu of Kenya, the dust devil is known as ngoma cia aka, in Brazil, a dust devil is called redemoinho after moinho de vento. In some traditions, it contains a dancing Saci, sometimes it is associated to local religion and beliefs. In Portugal it is known locally as remoinho, Dust devils form when hot air near the surface rises quickly through a small pocket of cooler, low-pressure air above it. If conditions are just right, the air may begin to rotate, the secondary flow in the dust devil causes other hot air to speed horizontally inward to the bottom of the newly forming vortex.
As more hot air rushes in toward the developing vortex to replace the air that is rising, a dust devil, fully formed, is a funnel-like chimney through which hot air moves, both upwards and in a circle. As the hot air rises, it cools, loses its buoyancy, as it rises, it displaces air which descends outside the core of the vortex. This cool air returning acts as a balance against the spinning hot-air outer wall, the spinning effect, along with surface friction, usually will produce a forward momentum
Winter is the coldest season of the year in polar and temperate climates, between autumn and spring. Winter is caused by the axis of the Earth in that hemisphere being oriented away from the Sun, different cultures define different dates as the start of winter, and some use a definition based on weather. When it is winter in the Northern Hemisphere, it is summer in the Southern Hemisphere, in many regions, winter is associated with snow and freezing temperatures. The moment of winter solstice is when the elevation with respect to the North or South Pole is at its most negative value, meaning this day will have the shortest day. The English word winter comes from the Proto-Indo-European root wend, relating to water, the tilt of the Earths axis relative to its orbital plane plays a large role in the formation of weather. The Earth is tilted at an angle of 23. 44° to the plane of its orbit, when it is winter in the Northern Hemisphere, the Southern Hemisphere faces the Sun more directly and thus experiences warmer temperatures than the Northern Hemisphere.
Conversely, winter in the Southern Hemisphere occurs when the Northern Hemisphere is tilted more toward the Sun, from the perspective of an observer on the Earth, the winter Sun has a lower maximum altitude in the sky than the summer Sun. During winter in either hemisphere, the altitude of the Sun causes the sunlight to hit that hemisphere at an oblique angle. In regions experiencing winter, the amount of solar radiation is spread out over a larger area. This effect is compounded by the distance that the light must travel through the atmosphere. Compared with these effects, the changes in the distance of the earth from the sun are negligible, the manifestation of the meteorological winter in the northerly snow–prone parallels is highly variable depending on elevation, position versus marine winds and the amount of precipitation. A case in point is Canada, a country associated with tough winters. Winnipeg on the Great Plains at a distance from large bodies of water has a January high of −11.3 °C.
In comparison, Vancouver on the coast with an influence from moderating Pacific winds has a January low of 1.4 °C with days well above freezing at 6.9 °C. Both areas are on the 49th parallel north and in the western half of the continent. Winter is often defined by meteorologists to be the three months with the lowest average temperatures. This corresponds to the months of December and February in the Northern Hemisphere, the coldest average temperatures of the season are typically experienced in January or February in the Northern Hemisphere and in June, July or August in the Southern Hemisphere. Blizzards often develop and cause many transportation delays, diamond dust, known as ice needles or ice crystals, forms at temperatures approaching −40 °F due to air with slightly higher moisture from aloft mixing with colder, surface based air
A waterspout is an intense columnar vortex that occurs over a body of water. Some are connected to a cumulus cloud, some to a cumuliform cloud. In the common form, it is a tornado over water. While it is weaker than most of its land counterparts. Most waterspouts do not suck up water, they are small, although rare, waterspouts have been observed in connection with lake-effect snow precipitation bands. Waterspouts exist on a microscale, where their environment is less than two kilometers in width, the cloud from which they develop can be as innocuous as a moderate cumulus, or as great as a supercell. While some waterspouts are strong and tornadic in nature, most are much weaker, weak tornadoes, known as landspouts, have been shown to develop in a similar manner. More than one waterspout can occur in the vicinity at the same time. As many as nine simultaneous waterspouts have been reported on Lake Michigan, waterspouts that are not associated with a rotating updraft of a supercell thunderstorm are known as non-tornadic or fair-weather waterspouts, and are by far the most common type.
Fair-weather waterspouts occur in waters and are associated with dark, flat-bottomed. Waterspouts of this type rapidly develop and dissipate, having life cycles shorter than 20 minutes and they usually rate no higher than EF0 on the Enhanced Fujita scale, generally exhibiting winds of less than 30 m/s. They are most frequently seen in tropical and sub-tropical climates, with upwards of 400 per year observed in the Florida Keys, fair-weather waterspouts are very similar in both appearance and mechanics to landspouts, and largely behave as such if they move ashore. A tornado which travels from land to a body of water would be considered a tornadic waterspout, however, in some areas, such as the Adriatic and Ionian seas, tornadic waterspouts can make up half of the total number. A winter waterspout, known as a devil, an icespout, an ice devil. The term winter waterspout is used to differentiate between the warm season waterspout and this rare winter season event. Very little is known about this phenomenon and only six known pictures of this event exist to date, four of which were taken in Ontario, there are a couple of critical criteria for the formation of a winter waterspout.
Very cold temperatures need to be present over a body of water enough to produce fog resembling steam above the waters surface. Like the more efficient lake-effect snow events, winds focusing down the axis of long lakes enhance wind convergence and they are not restricted to saltwater, many have been reported on lakes and rivers including the Great Lakes and the St. Lawrence River
An arcus cloud is a low, horizontal cloud formation, usually appearing as an accessory cloud to a cumulonimbus. Roll clouds and shelf clouds are the two types of arcus. Roll clouds may arise in the absence of thunderstorms, forming along the cold air currents of some sea breeze boundaries. A shelf cloud is a low, wedge-shaped arcus cloud, a shelf cloud is attached to the base of the parent cloud, which is usually a thunderstorm, but could form on any type of convective clouds. Rising cloud motion often can be seen in the part of the shelf cloud, while the underside often appears turbulent. Cool, sinking air from a storm clouds downdraft spreads out across the land surface and this outflow cuts under warm air being drawn into the storms updraft. As the lower cooler air lifts the warm moist air, its water condenses, creating a cloud which often rolls with the different winds above, people seeing a shelf cloud may believe they have seen a wall cloud. This is likely a mistake, since an approaching shelf cloud appears to form a wall made of cloud, a shelf cloud usually appears on the leading edge of a storm, and a wall cloud will usually be at the rear of the storm. A sharp, strong gust front will cause the lowest part of the edge of a shelf cloud to be ragged and lined with rising fractus clouds.
In a severe case there will be vortices along the edge, a very low shelf cloud accompanied by these signs is the best indicator that a potentially violent wind squall is approaching. An extreme example of this phenomenon looks almost like a tornado and is known as a gustnado, a roll cloud is a low, tube-shaped, and relatively rare type of arcus cloud. They differ from shelf clouds by being completely detached from other cloud features, roll clouds usually appear to be rolling about a horizontal axis. They are a wave called a soliton, which is a wave that has a single crest. One of the most famous frequent occurrences is the Morning Glory cloud in Queensland, one of the main causes of the Morning Glory cloud is the mesoscale circulation associated with sea breezes that develop over the Cape York Peninsula and the Gulf of Carpentaria. However, similar features can be created by downdrafts from thunderstorms and are not exclusively associated with coastal regions. Coastal roll clouds have been seen in places, including California, the English Channel, Shetland Islands, the North Sea coast, coastal regions of Australia.
Archived from the original on July 15,2013