Hail

Hail is a kind of solid ice that falls from the sky during certain storms. Each piece of hail is called a hailstone. Hailstones can be as small as a pea or as big as a baseball. Hail forms inside tall thunderstorm clouds, mostly during warm weather. This may sound strange, but hail almost never falls in winter. It needs the powerful winds of a summer thunderstorm to form.

Hail starts inside a type of cloud called a cumulonimbus. These are the giant, towering clouds that bring thunderstorms. Inside one of these clouds, strong winds called updrafts blow upward at high speeds. The updrafts carry tiny water droplets high into the cloud, where the air is freezing cold. The droplets freeze into small balls of ice.

Then the real fun begins. The frozen droplet falls a little, picks up more water, and gets blown back up by another updraft. The new water freezes onto the outside of the hailstone. This happens over and over. Each trip adds another layer of ice, like the rings inside a tree. If you cut a big hailstone in half, you can often see these layers.

A hailstone keeps growing until the updrafts can no longer hold its weight. Then it falls to the ground. The biggest hailstones come from the strongest storms, because only the most powerful updrafts can keep a heavy stone in the air long enough for it to grow. A baseball-sized hailstone falls at over 100 miles per hour, faster than a car on the highway.

Hail can do real damage. It dents cars, breaks windows, and shreds crops. Farmers in places like the Great Plains sometimes lose an entire field of corn or wheat in a single storm. The area where Colorado, Nebraska, and Wyoming meet gets so many hailstorms that scientists call it Hail Alley. Some places there get hail seven or more days every year.

People are sometimes confused about the difference between hail and sleet. Sleet is small frozen rain that falls in winter. Hail is much bigger and forms only in warm-weather thunderstorms. If you see ice falling from the sky in July, it is almost certainly hail.

If you ever pick up a fresh hailstone, look closely before it melts. The cloudy and clear layers inside are a record of its journey. Each ring shows one trip up and down inside a thunderstorm.