Hailstones Form
  You may be surprised to learn that most rain in the United States starts as snow. The temperature of the air high above the ground is often below 0ºC. Clouds of ice crystals form in the cold air. The ice crystals grow larger until they start to fall as snowflakes. As they fall, the crystals sometimes stick to other crystals and become larger snowflakes. If the temperature of all the air between the cloud and the ground is less than 0ºC, the ice crystals will fall to the ground as snowflakes.
  The ice crystals from a cloud may change as they fall through different layers of air. If the ice crystals fall into air that is warmer than 0ºC, they will melt and fall as rain. If the air near the ground is very cold, the rain sometimes freezes before it hits the ground. The frozen raindrops are sleet. Sleet and hail are not the same. They form in different ways. Freezing rain, also called an ice storm, is rain that freezes as soon as it hits the cold ground or other cold objects.
  How Hail Forms
  Hail forms when very strong winds blow upward into a cloud. These winds blow raindrops back up into the freezing air at the top of the cloud. This creates a small piece of ice. As the ice is blown through the cloud many times, many layers of water freeze on it. Finally, it gets too heavy for the winds to carry it back up. The hailstone falls to the ground. Most hailstones are about the size of a pea. Some can get bigger than a baseball.
How does sleet form?
    2. What happens to snow if it falls through a layer of warm air?
    3. Sequence the steps taken from water vapor to sleet.
  Upward winds carry hail through a cloud many times.
  Hail falls from a cloud when it is too big for the upward winds to lift it.