When it's sleeting and you hear that distinctive clattering on the roof and windshield of your car, you know what is happening: snowflakes are turning into small ice pellets before they hit the ground. But what is the difference between sleet and hail? Both forms of precipitation fall from clouds, but sleet and hail have different properties. They also occur during different weather conditions and require a specific set of circumstances to take shape.

Sleet is frozen rain that melts as it descends, then refreezes into tiny ice pellets before hitting the ground. It happens when snowflakes pass through a layer of warmer shallow air. This causes the flakes to melt a little and then refreeze quickly. The result is a sleet-like material that can accumulate very rapidly.

Hail, on the other hand, consists of large, layered ice balls that fall from powerful thunderstorms as supercooled water droplets strike with ice crystals and solidify. The resulting halos are usually ping-pong-ball sized, although hailstones up to seven pounds have been reported. Hail occurs during the summer months and is often accompanied by thunder.

Hail begins as raindrops in the bottoms of thunderclouds, which are usually warm and humid during a storm. Updrafts in a thundercloud carry these drops to the tops of the clouds, where the temperature is significantly colder. On the way, the cooled raindrops may come in contact with ice crystals or other debris in the cloud, which freezes on to the drops. This process can occur several times, causing the drops to grow in size until they become too heavy for the updraft to hold them and they fall to the ground as hail.