What is Hail
Hail is precipitation that consists of solid ice balls or lumps. Unlike sleet, which is frozen rain that falls as separate ice pellets, hail forms through a different process in clouds. Hail can range in size from tiny pellets similar to peas to large stones the size of baseballs or even larger in severe storms.
The Formation Process
Hail forms inside powerful thunderstorm clouds through a cycle of freezing and refreeze. A raindrop or water particle gets caught in a strong updraft, which is an upward-moving column of air inside the cloud. This updraft carries the drop high into the cloud where temperatures are well below freezing. The water droplet freezes into ice. However, it does not immediately fall to the ground.
Building Layers
As the ice particle falls slightly within the cloud, it encounters more liquid water droplets. These droplets freeze onto the ice particle, adding a new layer of ice. The strong updraft then pushes the particle back up again. This process repeats many times, with each cycle adding another layer of ice around the original core. Each layer is like a ring on a tree, and scientists can count these rings to understand how many times the hailstone went up and down in the cloud.
When Hail Falls
Eventually, the hailstone becomes so heavy that even the strongest updrafts cannot hold it up any longer. When this happens, the hailstone falls out of the cloud and toward the ground. If the air below the cloud is warm enough, some hailstones may melt before reaching the ground and turn into rain. If the air is cold enough, the hailstone reaches the ground as ice and does not melt.
Conditions for Hail
Hail requires very specific conditions to form. A thunderstorm must be strong enough to produce powerful updrafts that can suspend heavy ice particles. The storm also needs abundant moisture and cold air in the upper atmosphere. This is why hail is most common in spring and early summer when warm air near the ground meets cold air higher up. The central United States, particularly an area called Hail Alley in Colorado and Wyoming, experiences hail more frequently than other regions. 
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