Ever notice that the first drops of a thunderstorm are always the biggest? Ever wonder why? The reason is simply that only the heaviest drops can fall through the powerful updraft winds inside of a thunderstorm.
Early pilots who foolishly attempted to fly straight through towering thunderhead clouds quickly found out about the updrafts the hard way. Heavy airliners were turned upside down, and wings were ripped off Air Force bombers.
Pilots claimed that winds in excess of hurricane force (74 miles per hour) existed inside thunderheads. Those winds could blow rapidly upwards (an updraft) or downwards (a downdraft). Today, commercial airline pilots fly around such storms.
Many raindrops inside a developing thunderstorm are carried aloft by updrafts. While the lower part of a thunderhead cloud contains warm air, at altitudes above 25 thousand feet, air temperatures are always below freezing (32ºF). Water droplets at such high altitudes freeze, a process called riming or icing. In the early days of aviation before heaters were installed on airplanes, this icing caused many crashes and almost claimed the life of Charles Lindbergh, the first man to fly across the Atlantic Ocean.
Since most thunderheads can grow to 40 or even 50 thousand feet in height, it is possible for raindrops to be caught in an updraft, carried tens of thousands of feet aloft, and quick frozen into hail. An ice particle may actually be tossed up and down several times through a thunderhead, melting partially and refreezing, before finally becoming heavy enough to fall through the violent updrafts to the ground. Once a drop has frozen, other drops can freeze on it, and so a hailstone grows—sometimes into a huge ice ball.
Hailstorms are most frequent in eastern Wyoming, eastern Colorado, and western Nebraska. In some parts of the country—Florida, for instance—you can frequently encounter severe thunderstorms, but will rarely see hail. The reason is that in such very warm climates, hail will fall through a warm, moist layer of air at the bottom of the thunderstorm and will almost always melt before it reaches the ground. If you ever encounter a thunderstorm that drops hailstones, collect a few hailstones and examine them closely with a magnifying glass. With a sharp knife, try cutting one in half.
What do you see? What you may find are layers—several distinct lines around the center drop. That means the original large raindrop made several round trips up and down through the freezing zone before finally becoming heavy enough to resist the updraft and fall to the ground as hail.
Often, hail falls over areas of 100 feet to 2 miles wide and 5 to 10 miles (or more) long as a thunderstorm moves downwind. These areas, known as hailstreaks, can actually turn white from a heavy accumulation of hailstones. A severe storm on June 3, 1959, covered Selden, Kansas, with hailstones to a depth of 18 inches.
The total destruction of crops, especially in the Great Plains where hailstorms
are frequent, may result. Injury and even death may come to both animals and humans when caught in a heavy bombardment of large hail. Hailstones can range in size from that of a pea to that of a grapefruit. The largest hailstone ever measured fell at Coffeyville, Kansas, on September 3, 1970. It had a circumference of 17.5 inches and weighed 1.671 pounds. Ouch!