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.
Ice pellets are frozen raindrops. They are also called sleet. Ice pellets are usually quite small in size. Unlike snowflakes, 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 more droplets that freeze onto the hailstone, the longer the hailstone spends in the sky. When it finally grows too heavy to be held up by the flowing air, it falls to the ground.