How Are Hailstones Formed?
Hailstones are balls of ice that fall from storm clouds. Hail is a type of precipitation, or water in the atmosphere. Hail starts out as rain. As the raindrops form, air currents carry them to upper portion of the cloud, where it is freezing cold. There, the drops freeze into tiny icy balls. Higher still, the drops become coated with snow.
As they fall, the hailstones pick up a coating of rain. Each time the hailstones are hurled up and down by the wind, they accumulate another layer of ice and snow. Finally, the hailstones become too heavy to be held up in the cloud by the wind, and they fall to the ground.
Most hailstones measure between 5 millimeters and 15 centimeters in diameter, and can be round or jagged. Hail actually falls as a solid. Certain parts of the world receive more hail than others. The approach of the summer monsoon season in India brings severe thunderstorms, often with tornadoes and hail.
A particularly deadly hail storm in Moradabad, India, in 1888 killed more than 250 people. China also experiences frequent hail storms, as do parts of the Midwestern United States. In fact, the Great Plains region of the United States and Canada is called “Hail Alley.” The world record hailstone fell in Coffeyville, Kansas on September 3, 1970. It weighed 770 g.
Hailstones can cause extreme damage to buildings, vehicles, and crops. Not surprisingly, people have tried to find ways to prevent hail. In the 18th century, Europeans began trying to prevent hail by firing cannons into clouds and ringing church bells.
In the 20th century, Russia and the United States tried cloud seeding. Cloud seeding is adding chemical particles into clouds from rockets or aircraft. Cloud seeding is thought to control rain and hail. There is no clear evidence that any of these techniques are effective.