A hailstorm is precipitation in the form of balls or lumps of clear ice and compact snow. It is not known for sure how hailstones form and grow. We do know that they are spherical or irregularly spherical and usually vary in diameter up to 1/2 in. (1.3 cm); in rare cases hailstones having diameters up to 5 in. (12.7 cm) have been observed. Hail causes much damage and injury to crops, livestock, property, and airplanes.

Where: United States When: 1999 Major blizzard and sub-zero temperatures wreak havoc in Illinois, Wisconsin, Indiana, Michigan, and Ohio; 73 were killed in the blizzard and transportation systems in the region were paralyzed. Damages reached about $500 million.

Where: United States When: 1978 The blizzard of 1978 was one of the most powerful snowstorms to hit the East Coast. It crippled New York and New England for days, in many areas dumping more than three feet of snow.

Where: United States When: 1888 The worst winter storm in U.S. history, the Blizzard of 1888 surprised the northeastern United States with as much as five feet of snow in some areas. Two hundred boats sank and more than 400 people died due to very powerful winds and cold temperatures.

Where: Russia (formerly the Soviet Union) When: 1923 In Rostov, 23 people and even more cattle were killed by hailstones weighing up to 2 pounds each.

Where: India When: 1939 A hailstorm over a 30-square-mile area in the southern part of the country killed cattle and sheep and damaged crops. Some of the hailstones were said to weigh 71/2 pounds.

For other blizzards, see Major Storms: Blizzards.