# Hail - Source: Kiddle (kids.kiddle.co), CC BY-SA 3.0, Kiddle encyclopedia, adapted from Wikipedia - Reading level: Grade 5 - Subjects: Weather, Nature, Science - Topics: hail, hailstone, hailstones, cloud, larger, water - Length: 1229 words, about 9 min - Published: 2025-10-17 - Original: - Page: - Open in Sprouts: ![Granizo](https://sprout.rootsofreason.org/media/kiddle-hail-2a67f16af3.jpg) A large hailstone, about 6 centimeters (2.4 inches) across. **Hail** is a type of solid precipitation that falls from the sky. It's made of balls or irregular lumps of ice, and each piece is called a **hailstone**. Hail is different from **ice pellets** (also called sleet), which are smaller and usually fall in colder weather. Hailstones are typically larger than other icy precipitation like [snow](https://sprout.rootsofreason.org/r/kiddle/snow) or graupel. They usually measure between 5 millimeters (0.2 inches) and 15 centimeters (6 inches) across. When weather reports mention hail, "GR" means hailstones are 5 mm (0.2 in) or larger, while "GS" is used for smaller hailstones or graupel. Hail forms inside strong [thunderstorm](https://sprout.rootsofreason.org/r/kiddle/thunderstorms) clouds, especially cumulonimbus clouds. For hail to form, there needs to be powerful upward-moving air currents (called updrafts) within the storm. These updrafts keep the ice growing higher in the cloud. Hail is more common in the middle parts of continents, but in tropical areas, it usually happens at high elevations like mountains. Scientists use weather satellites and weather radar to find thunderstorms that might produce hail. Larger hailstones generally fall faster, but things like melting, air friction, and wind can slow them down. Weather warnings are issued when hailstones are big enough to cause damage, as they can harm buildings, cars, and especially farmers' crops. ## What is Hail? Any thunderstorm that produces hail reaching the ground is called a **hailstorm**. An ice crystal is considered a **hailstone** if it's larger than 5 millimeters (0.2 inches) in diameter. Some hailstones can grow very large, up to 15 centimeters (6 inches) across, and weigh more than 0.5 kilograms (1.1 pounds)! Unlike ice pellets, hailstones often have layers, like an onion. They can be clear or have alternating layers of clear and cloudy ice. These layers form as the hailstone travels through the cloud, held up by strong updrafts. It keeps growing until it gets too heavy for the updraft and falls to the ground. In the United States, damaging hail is often the size of a golf ball (about 4.4 centimeters or 1.75 inches). Hailstones larger than 2 centimeters (0.8 inches) are usually big enough to cause damage. Different countries have different rules for when they issue warnings. For example, areas that grow grapes might be affected by smaller hailstones. The size of hailstones depends on how strong the updraft is; stronger storms can hold larger hailstones up for longer, allowing them to grow bigger. ## How Hail Forms Hail forms in powerful [thunderstorm](https://sprout.rootsofreason.org/r/kiddle/thunderstorms) clouds. These clouds have strong updrafts, lots of water, and a large part of the cloud is below freezing (0 degrees Celsius or 32 degrees Fahrenheit). These strong updrafts can also be a sign that a [tornado](https://sprout.rootsofreason.org/r/kiddle/tornadoes) might form. ### The Layers of a Hailstone ![Hailshaft](https://sprout.rootsofreason.org/media/kiddle-hail-d87f39a312.jpg) A "hail shaft" – where hail is falling from a storm. Hail starts as tiny water droplets in the cloud. As these droplets rise higher, the temperature drops below freezing. They become "supercooled" water, meaning they are still liquid even below freezing. When they touch a tiny particle (a condensation nuclei), they freeze. If you cut a large hailstone in half, you might see layers, like an onion. For a long time, people thought this meant hailstones went up and down many times in the cloud, adding a new layer each time. However, new research shows this isn't always true. The storm's powerful updraft, with winds sometimes as fast as 110 miles per hour (177 km/h), pushes the forming hailstones up into the cloud. As a hailstone moves up, it passes through different parts of the cloud. Some areas have lots of water droplets, and others have more water vapor. - When the hailstone enters an area with many water droplets, it collects them and forms a clear, thick layer. - If it moves into an area with mostly water vapor, it forms a cloudy, white layer. ![Hail clouds](https://sprout.rootsofreason.org/media/kiddle-hail-8478e67386.jpg) Severe thunderstorms with hail can sometimes look green. The hailstone's speed also changes depending on where it is in the updraft and how heavy it is. This affects how thick each layer becomes. Larger hailstones tend to form a bit away from the strongest part of the updraft, where they can spend more time growing. As a hailstone grows, it releases heat, which keeps its outside surface a bit wet and sticky. This allows it to collide with and absorb smaller hailstones, growing even larger and sometimes forming irregular shapes. This is called "wet growth." Hail can also grow in a "dry growth" way. This happens when the outside of the hailstone freezes too quickly to stay liquid. Hail formed this way looks cloudy because tiny air bubbles get trapped inside. These bubbles usually escape during "wet growth," making the hailstone clearer. A hailstone can switch between wet and dry growth, which is why it has distinct layers. The hailstone keeps rising until it's too heavy for the updraft to hold it up. This can take at least 30 minutes in a strong thunderstorm, which can reach over 10 kilometers (6 miles) high. Then, it falls towards the ground, still growing as it leaves the cloud. It starts to melt as it falls into warmer air closer to the ground. So, a single journey through the storm can explain the layered look of a hailstone. Only in very rare cases, like in a multi-cell thunderstorm, might a hailstone be caught by another updraft. ### Where Hail is Most Common Hail is most common in the middle parts of continents, away from the coasts. This is because hail forms more easily when the freezing level in the atmosphere is lower, below about 11,000 feet (3,350 meters). Dry air moving into strong thunderstorms over land can make hail more likely. This dry air causes cooling, which lowers the freezing level, giving hail more space to grow. Because of this, hail is less common in tropical areas, even though they have many thunderstorms. The air in the tropics is usually warmer at higher altitudes. In tropical regions, hail mainly occurs at higher elevations, like in mountains. Hail growth slows down a lot when air temperatures drop below -30 degrees Celsius (-22 degrees Fahrenheit), as there are fewer supercooled water droplets at these very cold temperatures. ## Where Hail Happens Around the World Hail happens most often in the middle latitudes, inside continents. It's less common in tropical areas, even though tropical regions have more thunderstorms. Hail is also much more common near mountain ranges. Mountains force winds upwards (this is called orographic lifting), which makes the updrafts in thunderstorms stronger and increases the chance of hail. Also, at higher elevations, hail has less time to melt before it hits the ground. One area famous for large hail is northern [India](https://sprout.rootsofreason.org/r/kiddle/india), which had a very deadly hailstorm in 1888. China, Central Europe, and southern Australia also experience many hailstorms. In Europe, places like southern and western Germany, northern and eastern France, and northern Italy often get hail. In North America, hail is very common where Colorado, Nebraska, and Wyoming meet. This area is even called "Hail Alley." Hailstorms here usually happen between March and October, mostly in the afternoon and evening. Cheyenne, Wyoming gets more hailstorms than any other city in North America, with about nine to ten per season. Another "Hailstorm Alley" is in Alberta, Canada, just downwind of the Rocky Mountains. ## Picture credits - nssl0001, National Severe Storms Laboratory (NSSL) Collection, Public domain () - Bidgee, CC BY 2.5 () - Public domain ()