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- Hail is a type of solid precipitation consisting of many falling individual hailstones. Hailstones are rounded balls or irregular-shaped chunks of water-ice ranging in size from 0.2 to 2 inches in diameter. The biggest hailstone officially measured and recorded weighed 1.67 pounds and measured 17.5 inches in circumference. Clouds responsible for the production of hailstones often have a characteristic greenish tinge. Ice pellets are similar to small hailstones, but with a different structure.
- Hailstones grow inside large, high-altitude cumulonimbus thunderclouds, often called anvil-head clouds or thunderheads. High updraft and downdraft winds move supercooled water droplets up and down inside the cloud. Hailstones condense around a nucleus of dust particles, ice crystals or other pieces of tiny solid matter. Heat energy released by freezing sometimes melts the hailstone's outer layer, allowing accretion of water droplets and small hailstones. Eventually the hailstones grow too heavy for the updraft winds and fall to the ground.
- Hailstones consist of concentric circles of ice layers. A hailstone cut in half reveals an onion-like structure of thick, translucent layers interspersed with thin, white opaque layers. The ice rings are formed as the hailstone travels from the top to the bottom of the cumulonimbus cloud. The hailstones descend into humid, moist zones, picking up coats of water that freezes as the hailstones rise to the subfreezing upper zones of the cloud. The opaque hailstone layers often contain tiny air bubbles.
- Hailstones fall in defined areas called hail swaths by meteorologists. Large swaths of hailstones can reach 10 miles wide by 100 miles long. Sometimes the hailstones accumulate in drifts requiring snowplows to clear the roads. In 1990, a hailstone struck and killed a man in Lake Worth, Texas. Also in 1990, a hailstorm seriously injured 47 people stuck on a Ferris wheel in Denver, Colorado. The contiguous region of Colorado, Wyoming and Nebraska is known as "Hail Alley" and averages seven to nine hail storms annually.
Hail
Formation
Structure
Damaging Characteristics
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