Precipitation's Type by the Distribuion of Temperature
 | In the image (left) the green dashed line is the temperature in respect to elevation. The surface temperature is 25°F (-4°C) and increases with height before decreasing. However, since the temperature remains below freezing any precipitation that falls will remain as snow. |
 | In this image the surface temperature is higher, 27°F (-3°C). Also as elevation increases, the temperature increases to a point where some of the atmosphere is above freezing before the temperature lowers again below freezing. As snow falls into the layer of air where the temperature is above freezing, the snow flakes partially melt. As the precipitation reenters the air that is below freezing, the precipitation will re-freeze into ice pellets that bounce off the ground, commonly called sleet. The most likely place for freezing rain and sleet is to the north of warm fronts. The cause of the wintertime mess is a layer of air above freezing aloft. |
 | Freezing rain will occur if the warm layer in the atmosphere is deep with only a shallow layer of below freezing air at the surface. The precipitation can begin as either rain and/or snow but becomes all rain in the warm layer. The rain falls back into the air that is below freezing but since the depth is shallow, the rain does not have time to freeze into sleet. Upon hitting the ground or objects such as bridges and vehicles, the rain freezes on contact. Some of the most disastrous winter weather storms are due primarily to freezing rain. |
How are Hailstones formed?
Hailstones are formed inside cumulonimbus clouds, where freezing water droplets are put in motion by strong winds. This is how a hailstone is formed:
1. Moved by downward winds, a drop of freezing water goes to the lowest and warmest part of the cloud. There, it picks up a layer of clear ice made up of the surrounding water droplets and starts to form a hailstone.
2. Lifted by upward-moving winds, the tiny hailstone then rises to the top of the cloud. There, freezing air causes the water droplets that are clinging to the hailstone to freeze instantly. It grows in size as it is covered in a coating of white ice.
3. After moving up and down several times by the winds in the cloud, the hailstone is gradually coated in more layers of ice. Once it grows too heavy to be supported by the winds, the hailstone falls to the ground.
 | Hailstones move up and down inside cumulonimbus clouds for 5 to 10 minutes before falling to the ground. While traveling inside the cloud, they may pick up as many as 25 layers of ice. |
The Life and Times of Snowflakes
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