Hail looks like tiny balls of ice that skitter along the ground when they land. But not all hail is small. According to the National Weather Service the largest verified hailstone, the name for a ball of hail, was found in Gotebo, Oklahoma on May 23, 2011. It measured 6 inches across. Others have reported hailstones the size of baseballs that fell with enough force to break car windows. But, how do these giant hailstones form? If you've ever blown soap bubbles and watched them drift in the air, you already have clue to how hailstones are created.
Hailstones begin their life in a thunderstorm cloud as a tiny droplet of water. But life in a thundercloud can get pretty chaotic when cold and warm air currents collide. It is these air currents, and the difference in air temperature, that causes hailstones to form.
When the water droplet lands in a warm air current it is lifted upward, much like soap bubbles in the breeze. The air current takes the water droplet high into the cloud where temperatures are below freezing. The droplet freezes into a tiny ball of ice.
When the hailstone freezes it may be caught by a cold downdraft of air that pulls it downward rapidly. As it falls to lower levels where the temperatures are warmer, it begins to melt. Normally, the hailstone melts completely and falls to the ground as rain. But, sometimes, the hailstone is caught up in another warm current that carries it upward to freezing temperatures. When this happens the hailstone forms another layer of ice.
A Vicious Cycle
If the hailstone is repeatedly carried upward and then falls and begins to melt, the hailstone grows larger each time it freezes. Eventually, it gets too heavy and falls to the earth. Because the stone is so big, it does not have time to melt before it reaches the ground.
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