Hail is formed by the layered freezing of water into ice in a strong thunderstorm.
Hail is formed when clouds, specifically cumulonimbus clouds, have both high altitudes and powerful updrafts within the condensation layer of the cloud. As rain droplets form, they are frozen and then carried aloft again, where their temperature condenses additional water on the exterior, which then also freezes. After an extended period of gaining an increasing number of ice layers, the hailstones at some point are too heavy for the updrafts to lift, and they fall to the ground, sometimes losing layers to melting in the warmer air below.
Hailstones from powerful storm clouds can reach a diameter of more than 6 inches (15 cm), and weigh a pound (.5 kg) or more. They are often clumped together or have irregular shapes due to the method of their formation.
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