Hail Basics What is hail? Hail is a form of precipitation that occurs when updrafts in thunderstorms carry raindrops upward into extremely cold areas of the atmosphere where they freeze into ice. How does hail form? Recent studies suggest that supercooled water may accumulate on frozen particles near the back-side of the storm as they are pushed forward across and above the updraft by the prevailing winds near the top of the storm. Eventually, the hailstones encounter downdraft air and fall to the ground. Hailstones grow two ways: by wet growth or dry growth processes. In wet growth, a tiny piece of ice is in an area where the air temperature is below freezing, but not super cold. When the tiny piece of ice collides with a supercooled drop, the water does not freeze on the ice immediately. Instead, liquid water spreads across tumbling hailstones and slowly freezes. Since the process is slow, air bubbles can escape resulting in a layer of clear ice. Dry growth hailstones grow when the air temperature is well below freezing and the water droplet freezes immediately as it collides with the ice particle. The air bubbles are "frozen" in place, leaving cloudy ice. How fast does hail fall? We really only have estimates about the speed hail falls. One estimate is that a 1cm hailstone falls at 9 m/s, and an 8cm stone, weighing .7kg falls at 48 m/s (171 km/h). Can hail be forecast or predicted? To forecast hail, deep moist convection is required, in addition to these three basic ingredients: Adequate updraft to keep the hailstone aloft for an appropriate amount of time. Sufficient supercooled water near the hailstone to enable growth as it travels through an updraft. A piece of ice or snow for it to grow upon Random Hail Facts About 24 people are injured each year by hail in the U.S. The larger the hail, the stronger the thunderstorm. Hail rarely causes fatalities. The largest hailstone ever recovered in the United States fell in Aurora, Nebraska on June 22, 2003, with a record 7-inch diameter and a circumference of 18.75 inches. The heaviest hailstone ever documented in the U.S. fell in Coffeyville, Kansas on September 3, 1970, weighing in at 1.65 pounds. This information brought to you by Your Name.