The Science Behind the Formation of Hail


Have you ever seen hailstones? Sometimes they are tiny, sometimes they are large pellets of ice, which fall from the sky. Have you wondered how hail storms are formed and why it hails?

It is fall/winter season again, as students of Eastern Mediterranean University experience change in the weather conditions and gone are the long hot summer days, subsiding to cloud and rain. Recently we have experienced a lot of rainfall, particularly with the storm that hit Cyprus last week and devastated towns across the island and the unfortunate loss of lives. Hailstorms are quite a sight, which is a type of precipitation from our atmosphere. Hail is formed when drops of water freeze together in the cloud upper regions of thunderstorm clouds. These chunks of ice are called hailstones. Most hailstones measure between 5 millimeters and 15 centimeters in diameter and can be round or jagged. Hailstones are formed by layers of water attaching and freezing in a large cloud. A frozen droplet begins to form a cloud during a storm, but is pushed back up into the cloud by a strong updraft of wind. When these hailstones are lifted, it hits liquid water droplets. Those droplets then freeze to the hailstone, adding another layer to it. The hailstones eventually fall to earth when it becomes too heavy to remain in the cloud or when the updraft stops or slows down. Later it will start melting as it passes over air higher than freezing temperatures and finally the cloud starts dropping as hailstones.

The amount of water droplets which sticks on to the hailstone depends on velocity. However, the rate of formation of hailstones varies due to the changing super cooled water and humidity conditions. Apart from the formation under high humidity conditions, hailstones can also be formed through dry growth process. The hail formed through this process is opaque because small air bubbles are trapped as a result of fast freezing. However the bubbles may escape later making the hail clearer.


No matter it’s size, hail still poses major risks. Small hail (half an inch in diameter) can reach speeds of 20mph and usually comes down in larger quantities than big hails, creating a greater risk of damage. The typical scale of a hail storm varies considerably as it falls in paths known as swaths or streaks which can cover anywhere from a few acres to 100 miles wide and 10 miles long. Dense swaths of hail of any size can do serious damage to both people and property. In order to be safe, it is best to stay indoors until the storm completely passes, stay away from window and doors, and if you’re driving try to get somewhere safe like a garage or a gas station that’s nearby. Avoid ditches and low area that could suddenly flood. Most types of hail can pose a significant risk to you and your property but with a little upfront preparation and some common sense safety measures, you can keep yourself safe whenever this weather threat emerges.


Faith Edigin