Learning About Hail
Hail is a weather phenomenon that can damage homes, vehicles and crops. It could even lead to death. Large hail results in nearly $1 billion a year in property damage, and while death from hail is rare in the U.S., the last recorded fatality was a Colorado infant in 1979. Deaths from hail are more common in underdeveloped parts of the world where people live in poorly constructed buildings.
What is Hail?
Hail is a large frozen raindrop produced by intense thunderstorms. It is considered to have a diameter of at least 5 mm.
How is hail formed?
Hail forms when strong currents of rising air, called updrafts, carry water droplets high enough in a thunderstorm for the water to freeze. More and more water freezes, causing the piece of hail to grow in size. Once the frozen pellet is too heavy for the updrafts to keep it within the cloud, it begins to fall, hurtling toward the ground as fast as 90 mph.
The stronger the updraft, the bigger the hailstones can grow. Most hailstones are smaller than a dime, but stones weighing more than a pound have been recorded.
Three Forms of Hail
Hail can be classified into three stages of development: grauple, small hail and hailstones.
- Grauple: Soft, opaque hail with a snowflake-like structure that bounces off of hard surfaces, also referred to as snow pellets.
- Small hail: Has a higher density than grauple, and is usually semi-transparent and rounded, typically up to a 1/5 inch in diameter.
- Hailstones: Round stones of ice, with layers that look like an onion. The layers are formed while the hail is rising and falling in the updrafts.
Hail chart-with examples
- In the U.S., hailstorms are most common in the Central Plains, especially just east of the Rockies.
- Hail is always produced by cumulonimbus thunderclouds.
- Hail forms on condensation nuclei like dust, insects or ice crystals, when supercooled water freezes on contact.
- Cut in half, a hailstone has concentric rings like an onion, which reveals the number of times it traveled to the top of the storm before falling to Earth.
- The largest hailstone ever reported was 17.5 inches around, 5.5 inches wide and 1.67 pounds. The hailstone fell on September 3, 1970, in Coffeyville, Kansas.
- When hail falls to Earth it travels at 70 to 100 mph.
- Hail tends to occur in warm weather because hot air rising from the ground creates the turbulent updrafts and tall clouds necessary to keep the ice particles aloft for a long enough time to form hail.