Hail is a form of solid precipitation which consists of balls or irregular lumps of ice, that are individually called hail stones. Hail stones consist mostly of water ice and measure between 0.20 inches and 5.9 inches in diameter, with the larger stones coming from severe thunderstorms. Hail is possible with most thunderstorms as it is produced by thunderclouds, usually at the leading edge of a severe storm system. Hail is possible within 2 nautical miles (3.7 km) of its parent thunderstorm. Hail formation requires environments of strong, upward motion of air with the parent thunderstorm (similar to tornadoes) and lowered heights of the freezing level. Hail is most frequently formed in the interior of continents within the mid-latitudes of Earth, with hail generally confined to higher elevations within the tropics.
Unlike ice pellets, 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 0.039 inches thick, which are deposited upon the hail stone as it cycles through the cloud multiple times, suspended aloft by air with strong upward motion until its weight overcomes the updraft and falls to the ground. There are methods available to detect hail-producing thunderstorms using weather satellites and radar imagery. Hail stones generally fall at faster rates as they grow in size, though complicating factors such as melting, friction with air, wind, and interaction with rain and other hail stones can slow down their descent through Earth’s atmosphere. Severe weather warnings are issued for hail when the stones reach a damaging size, as it can cause serious damage to man made structures, and most commonly, farmers’ crops. The National Weather Service issues severe thunderstorm warnings for hail 1″ or greater in diameter. This threshold, effective January 2010, marked an increase over the previous threshold of 3/4″ hail. The change was made for two main reasons: a) public complacency and, b) recent research suggesting that damage does not occur until a hailstone reaches 1″ in diameter.
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.
Photo By: MissTessmacher