HAILSTONES are the result of freezing conditions and strong updrafts in cumulonimbus clouds. Updrafts carry water droplets above the freezing line in clouds and allows the water to freeze around a nucleus. As the solid ice passes repeatedly up through the freezing zone in the cloud it gets an additional coating of ice. Eventually the hailstone grows in size until the updrafts can no longer keep them aloft.
These hailstones formed during a summer thunderstorm is South Dakota. The
largest is about 1 inch in diameter and clearly shows the concentric freeze/melt
pattern produced as it was carried aloft by strong updrafts in the cumulonimbus
cloud.