61 Hailstorms-Mid

Hailstorms FOCUS Question What causes hailstorms?

What Is Hail? You're walking home on a hot summer day when suddenly the sky becomes dark. A loud BOOM of thunder startles you. Then countless balls of ice start falling from the sky. Ice on a hot summer day? You bet—it's a hailstorm! Hail is a form of frozen precipitation— water that falls from the sky to the ground. It is made up of balls, or pellets, of ice. A single piece of hail is called a hailstone. Hailstones are usually about the size of a pea, but they can be as large as a grapefruit.

The Ups and Downs of Hail In the United States, the only cold thing people usually think about in summer is ice cream. While sleet and snow fall in winter, hail normally falls in summer from a type of cloud called cumulonimbus (KYOOM-yuh-low NIM-bus). These clouds produce thunderstorms. Thunderstorms have just the right conditions for making hail. They have updrafts—air that flows upward at high speeds—and supercooled water droplets. These tiny raindrops are below the freezing point but have not yet frozen solid. Strong updrafts catch the supercooled droplets, hurling them high up in the cloud. Here, cold air freezes them, either alone or around tiny ice crystals that form the center of hailstones. Once they get heavy enough, the hailstones start to fall.

While falling through the air, small hailstones may get caught in updrafts and pulled higher again. More supercooled water freezes around them and they grow. The hailstones grow larger and larger as they gain more layers through a process called accretion. Updrafts can force hailstones upward over and over; the hailstones grow by accretion and then fall. The more often the cycle repeats, the larger the hailstones grow. This cycle continues until the hailstones get too heavy and fall all the way to the ground. Strong storms have powerful updrafts that can make very large hailstones before they fall to the ground.

Look Out Below! Some people refer to hail as "the white plague" because hail can cause millions of dollars in damage! Rock-hard hailstones can cause serious damage to crops, cars, buildings, and aircraft. Even small hailstones can crush plants, dent cars, break windows, and harm animals. Although it is rare, people and other animals can die from hail. Hailstorms can occur anywhere thunderstorms happen. In the United States, hail most often occurs in the Great Plains states in the middle of the country. This area is known as Hail Alley. Wowser! Hailstones hurtle toward the ground at speeds up to 145 kilometers (90 mi.) per hour!

Hail Events On July 23, 2010, a terrible thunderstorm hit Vivian, South Dakota. Afterward, a man named Les Scott spotted something amazing. It was a huge hailstone about the size of a volleyball! His find broke the record for the largest and heaviest hailstone in the United States. The deadliest hailstorm happened in India on April 30, 1888. The storm killed at least 246 people in an area outside Delhi. RECORD-BREAKING HAILSTONES IN THE UNITED STATES Measurement Data Date Location largest (circumference) 47.6 cm (18.75 in.) June 22, 2003 Aurora, Nebraska largest (diameter) 20.3 cm (8 in.) July 23, 2010 Vivian, South Dakota heaviest 0.88 kg (1.94 lb.) July 23, 2010 Vivian, South Dakota