When we think of icy precipitation falling from the sky, we usually think of snow. But there are other types of icy precipitation too.
Graupel are snowflakes that have become encrusted with ice. This happens when snowflakes pass through a chilly cloud on their way down and water droplets freeze on them, covering the snowflakes in a layer of ice.
Ice pellets are frozen raindrops. They are also called sleet. Ice pellets are usually quite small. Unlike snowflakes, they do not have a crystal shape.
Hail forms when a frozen raindrop or graupel is kept from falling to the ground by air flowing upward in a thunderstorm. The longer a hailstone spends in the clouds, the more droplets freeze onto it and the larger it gets. When it finally grows too heavy to be held up by the rising air, it falls to the ground.