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Definition
The HailStorm is a storm during which hail falls storm, violent storm - a violent weather condition with winds 64-72 knots (11 on the Beaufort scale) and precipitation and thunder and lightning Any thunderstorm which produces hail that reaches the ground is known as a hailstorm.Hail has a diameter of 5 millimetres (0.20 in) or more.Hail stones can grow to 15 centimetres (6 in) and weigh more than 0.5 kilograms (1.1 lb).

hail stones are layered and can be irregular and clumped together. Hail is composed of transparent ice or alternating layers of transparent and translucent ice at least 1 millimetre (0.039 in) thick, which are deposited upon the hail stone as it cycles through the cloud, suspended aloft by air with strong upward motion until its weight overcomes the updraft and falls to the ground. Although the diameter of hail is varied, in the United States, the average observation of damaging hail is between 2.5 cm (1 in) and golf ball-sized (1.75 in).

Stones larger than 2 cm (0.75 in) are usually considered large enough to cause damage. The Meteorological Service of Canada will issue severe thunderstorm warnings when hail that size or above is expected.The US National Weather Service has a 2.5 cm (1 in) or greater in diameter threshold, effective January 2010, an increase over the previous threshold of ¾-inch hail.Other countries will have different thresholds according local sensitivity to hail; for instance grape growing areas could be adversely impacted by smaller hailstones. Hailstones can be very large or very small, depending on how strong the updraft is: weaker hailstorms produce smaller hailstones than stronger hailstorms (such as supercells). Hail forms in strong thunderstorm clouds, particularly those with intense updrafts, high liquid water content, great vertical extent, large water droplets, and where a good portion of the cloud layer is below freezing 0 °C (32 °F) causes Tornado.

Factors Favouring HailStorm

Hail is most common within continental interiors of the mid-latitudes, as hail formation is considerably more likely when the freezing level is below the altitude of 11,000 feet (3,400 m).Movement of dry air into strong thunderstorms over continents can increase the frequency of hail by promoting evaporational cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in.Accordingly, hail is actually less common in the tropics despite a much higher frequency of thunderstorms than in the mid-latitudes
because the atmosphere over the tropics tends to be warmer over a much greater depth. Hail in the tropics occurs mainly at higher elevations.Hail growth becomes vanishingly small when air temperatures fall below −30 °C (−22 °F) as supercooled water droplets become rare at these temperatures.Around thunderstorms, hail is most likely within the cloud at elevations above 20,000 feet (6,100 m). Between 10,000 feet (3,000 m) and 20,000 feet (6,100 m), 60 percent of hail is still within the thunderstorm, though 40 percent now lies within the clear air under the anvil. Below 10,000 feet (3,000 m), hail is equally distributed in and around a thunderstorm to a distance of 2 nautical miles (3.7 km).

Causes of HailStorm
HailStorms are caused when moist, warm air rises from the Earth's surface. This moist, warm air cools as it rises and condenses to form clouds. If there is a lot of warm air rising, it can reach up to 12 miles (19 kilometers) high. Cool air moving downwards (known as a 'Downdraught') and warm air moving upwards (known as an 'Updraught') create the energy and electricity which produce the thunderstorms lightning and thunder. The average thunderstorm lasts for 30 minutes but can last for hours and be as large as 10km wide.
HailStorms can happen anywhere where the right conditions are present. They are most likely to form during late spring and summer and typically happen between late afternoon and evening. If you see lightning you can tell how far away the Thunderstorm is from you by listening for thunder. By counting the number of seconds between the lighting and the thunder you can work out how far away the thunderstorm is. Remember, thunder is simply sound caused by the lightning.

Hazards of HailStorm

Hail can cause serious damage, notably to automobiles, aircraft, skylights, glass-roofed structures, livestock, and most commonly, farmers' crops.Hail damage to roofs often goes unnoticed until further structural damage is seen, such as leaks or cracks. It is hardest to recognize hail damage on shingled roofs and flat roofs, but all roofs have their own hail damage detection problems.Metal roofs are fairly resistant to hail damage, but may accumulate cosmetic damage in the form of dents and damaged coatings. Hail is one of the most significant thunderstorm hazards to aircraft.When hail stones exceed 0.5 inches (13 mm) in diameter, planes can be seriously damaged within seconds.The hailstones accumulating on the ground can also be hazardous to landing aircraft. Hail is also a common nuisance to drivers of automobiles, severely denting the vehicle and cracking or even shattering windshields and windows.Wheat, corn, soybeans and tobacco
are the most sensitive crops to hail damage.Hail is one of Canada's most expensive hazards.Rarely, massive hailstones have been known to cause concussions or fatal head trauma. Hailstorms have been the cause of costly and deadly events throughout history. One of the earliest recorded incidents occurred around the 9th century in Roopkund, Uttarakhand, India.The largest hailstone in terms of diameter and weight ever recorded in the United States fell on July 23, 2010 in Vivian, South Dakota; it measured 8 inches (20 cm) in diameter and 18.62 inches (47.3 cm) in circumference, weighing in at 1.93 pounds (0.88 kg).This broke the previous record for diameter set by a hailstone 7 inches diameter and 18.75 inches circumference (still the greatest circumference hailstone) which fell in Aurora, Nebraska in the United States on June 22, 2003, as well as the record for weight, set by a hailstone of 1.67 pounds (0.76 kg) that fell in Coffeyville, Kansas in 1970.
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