Hail is not even the same thing as sleet. Not even close.
Freezing rain, raindrops that freeze once they hit the ground—occurs only during wintry, subfreezing weather. Hail, on the other hand, almost exclusively falls during thunderstorm season between spring and early fall.
Here’s how hail happens. When thunderstorm clouds gather together from heat and moisture, they often reach great heights, swirling up into low-temperature regions of the sky. The swirling warm and cold air rotates up and down within these cloud formations.
Rather than falling normally, raindrops can get stuck in a cold, windy loop that occurs in the higher, colder regions of the storm. When this happens, they can collide with other freezing and thawing drops, forming an even larger drop.
The longer a drop is in this loop cycle between the warm and cold areas of the storm clouds, the bigger it gets— attracting more water vapor, joining with other similar drops, freezing, partially thawing, and refreezing again.
Finally the weight of the hailstone becomes great enough for it to fall out of the windy loop inside the storm cloud. It falls to the ground as a round and painful chunk of ice.
