Leaf, Branch, Trunk
Damage, symptoms and biology
Evaporation caused by the sun's heat increases the level of humidity in the air. The warmed air, which is less dense, rises and as it rises, the humid air condenses and cools, eventually reaching a saturation point. That is when the droplets of water form clouds. If a thunderstorm cell forms, it is cooled more and more by the air, reaching temperatures of - 40°C to - 55°C. These low temperatures exist in the upper part of the cloud at altitudes ranging from 8 000 m (25 000 ft) to 12 000 m (40 000 ft). The resulting ice falls to the ground as hail. Minor damage to trees may include lacerations and perforations of foliage. Deep lacerations of the bark of twigs in the upper part of the tree are a more serious type of damage. These injuries can reduce sap flow in the distal portion of the wound and cause wilting of the foliage.
A hailstone normally has a diameter varying between 1 and 2 cm. In 1986, hailstones the size of tennis balls (8 cm in diameter) fell in Montreal. But the largest hailstones on record fell in Nebraska in 1928; they were 44 cm in diameter and weighed 744 grams.
Canadian Forest Service Publications
Information on host(s)
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