Hail

Hail is ice that falls from the sky.

It can look like small balls or lumps.

Hail forms in big storm clouds. Strong winds blow upward inside the clouds. These winds push water up into the cold air.

The water freezes into ice. As it moves, it grows more layers. These layers can look like an onion.

Large stones fall very fast. They can hit cars or farm food.

Some hail is tiny. Other hail can be as big as a golf ball. It is a very cool thing to see.

Hail is ice that falls from the sky during storms.

It can be small lumps or big balls. Most hailstones are made of layers of ice. These layers look like an onion.

Hail forms inside big thunderstorm clouds. These clouds have strong updrafts. An updraft is a wind that blows upward. This wind pushes water droplets high into the cold air. The droplets freeze into ice. As they move, they collect more water. This makes the ice grow. If they find lots of water, they get clear layers. If they find water vapor, they get white layers.

The ice stays up as long as the wind is strong. Once the stone is too heavy, it falls. Large stones fall very fast. They can break things like cars or farm crops.

Scientists use radar to find storms that make hail. In the United States, many storms happen in Hail Alley. This area includes Colorado, Nebraska, and Wyoming. In the tropics, hail mostly happens on high mountains.

Hail is a special kind of frozen rain. It falls as balls or irregular lumps of ice. These pieces are called hailstones.

While people often mix them up with ice pellets, hail is different. Ice pellets are usually smaller and see-through. Hailstones can grow much larger. They can even weigh more than one kilogram.

Hail can be very small or very large. Large stones can cause serious damage to buildings and farm crops.

Because they can be dangerous, weather services issue warnings when big hail is expected.

How does a hailstone grow? It all starts inside a large thunderstorm cloud. These clouds have strong updrafts. An updraft is a wind that blows upward very fast. This wind pushes water droplets high into the freezing parts of the cloud.

As these droplets freeze, they become hailstones. The stone grows by collecting more water as it travels. If it hits lots of liquid water, it gets a clear layer. If it hits water vapor, it gets a white, cloudy layer.

This creates an onion-like pattern of layers inside the stone.

The stone keeps rising until it becomes too heavy for the wind to hold.

Scientists study hail to understand these powerful storms. In the United States, a huge project began in Spring 2025. It is called ICECHIP. This study involves 100 scientists from four different countries. They are looking at "hail alleys" in the Great Plains and the Rocky Mountains.

This is the largest field study ever done just for hail. By studying how stones grow, they can learn more about the atmosphere. They use weather radar and satellites to track these storms. This helps people stay safe during severe weather.

Different parts of the world see hail in different ways. In the United States, many storms happen in an area called "Hail Alley." This is where Colorado, Nebraska, and Wyoming meet. Cheyenne, Wyoming, is a very hail-prone city.

In South America, Argentina has many storms every year. Some parts of Brazil and Colombia see them too. In the tropics, hail is less common. It usually only happens high up on mountains. This is because the air in the tropics is often too warm for hail to grow easily.

Think about how a kite stays in the air. A strong wind pushes the kite up against gravity. A hailstone is like that kite. The upward wind in a thunderstorm keeps the ice floating.

Eventually, the hailstone gets too heavy for the wind. Just like a heavy kite might fall, the hailstone falls to the ground. As it falls, it might even grow more. It can also start to melt if the air below is warm. This is why hail is such a busy and active part of our weather.

Hail is a specific type of solid precipitation consisting of balls or irregular lumps of ice. Each individual piece is called a hailstone.

While many people confuse it with ice pellets, or sleet, hail is quite different. Ice pellets are generally smaller, translucent, and fall during cold weather. Hail growth is actually inhibited by low surface temperatures. Hailstones can vary greatly in size, but they are often much larger than ice pellets or snow. In the United States, damaging hail is often observed between 1 and 2 centimeters in diameter.

A hailstone is officially defined as an ice crystal with a diameter greater than 5 millimeters. Some hailstones can grow to weigh more than one kilogram.

The formation of hail requires very specific atmospheric conditions within a thunderstorm. These storms must be cumulonimbus clouds, which are large and tall. Hail formation needs environments with strong upward motion of air, known as updrafts. These updrafts can have wind speeds as high as 150 kilometers per hour. The cloud must also have a high liquid-water content and a large vertical extent. Additionally, a significant portion of the cloud layer must be below the freezing level. When these conditions meet, water droplets are pushed high into the freezing parts of the storm.

Hailstones grow through a process of collecting water as they move through the cloud. This growth can happen in two different ways: wet growth and dry growth. In wet growth, the hailstone releases latent heat as it freezes. This heat keeps the outer layer of the stone in a liquid phase. Because this layer is sticky, the stone can grow by colliding with other smaller hailstones. This often results in irregular shapes. In dry growth, the latent heat is not enough to keep the surface liquid. This results in an opaque, white appearance because small air bubbles become trapped during rapid freezing.

As a hailstone travels, it develops a unique internal structure. If you look at a cross-section, it often shows an onion-like pattern of layers. This happens because the concentration of humidity and supercooled water droplets varies throughout the cloud. When a stone moves into an area with many liquid water droplets, it acquires a translucent layer. If it moves into an area with mostly water vapor, it acquires an opaque white layer.

The stone will continue to rise in the updraft until its mass becomes too great. This process of being suspended aloft can take at least 30 minutes. Eventually, the weight overcomes the updraft, and the stone falls toward the ground.

Geography plays a major role in where hail occurs. In the mid-latitudes, hail is most common near the interiors of continents. In the tropics, hail is less common because the atmosphere stays warm at higher altitudes. In tropical regions, hail is mostly confined to high elevations. Hail is also very common along mountain ranges. This is because mountains cause orographic lifting, which forces horizontal winds upward. This intensifies the updrafts in thunderstorms and makes hail more likely. High elevations also mean there is less time for the hail to melt before hitting the ground.

Certain regions are famous for frequent hailstorms. In North America, an area where Colorado, Nebraska, and Wyoming meet is called "Hail Alley." Cheyenne, Wyoming, is considered the most hail-prone city in North America. In South America, the central region of Argentina sees between 10 and 30 storms per year. This region includes Mendoza and Córdoba. Other areas with frequent hail include parts of Brazil, Paraguay, Uruguay, and Bolivia. In Europe, frequent hail is seen in southern and western Germany, northern Italy, and parts of the Balkans.

Because large hail can cause serious damage, scientists work hard to study it. Large stones can damage human-made structures and destroy farmers' crops. To help predict these events, meteorologists use weather satellites and radar imagery. For example, a "three-body spike" on radar can indicate hail.

In Spring 2025, a massive field study called ICECHIP began in the United States. This project involves 100 scientists from four countries. They are studying "hail alleys" in the Great Plains and the Rocky Mountains. This is the largest field campaign ever dedicated to studying hail. It aims to answer many remaining questions about how these stones form and grow.