Hail forms when water vapor in a storm cloud forms ice droplets around debris in the cloud, such as dust, salt or small insects. A storm cloud is formed when cool air meets warm air as it rises. The hailstones continue growing in the storm cloud until they fall to the ground.
- Form a storm cloud
The proper conditions for hail are created when rising warm air collides with sinking cool air from the upper atmosphere. When the clouds form at altitudes of 50,000 feet or more, water vapor within the cloud super-cools, meaning it remains a liquid at temperatures below 32 degrees Fahrenheit.
- Add particulate matter
The rising air brings debris to the cooler air, which condenses around the particles and freezes into balls of ice. The stones may fall down immediately when they form, but they can also be pushed into the cloud if the updraft is strong enough.
- Continue adding layers until the hail falls
The hailstones continue growing bigger and denser until they are too heavy to be kept afloat by the updraft. It is at this point that hailstones start falling to form a hailstorm. The size of the hailstones vary depending on the strength of the storm.