Sleet is usually snow that has half-melted, or it can be formed from rain-drops that have partly evaporated and then cooled down as they fall to the ground. It often feels like very cold, wet rain when it falls on you.
Sleet is rain or melted snow that freezes into ice pellets before hitting the ground. Sleet only happens under very specific weather conditions.
There must be a layer of air near the ground whose temperature is below freezing, where water turns to ice. Above this layer of freezing air must be a layer of warmer air. As snow falls through the warm air, it melts or partially melts into raindrops. As the melted snow falls through the cold layer of air, it re-freezes. It forms ice pellets, or sleet, before hitting the ground.
Sleet falls as tiny, hard pieces of ice. Sleet usually cannot do severe damage to crops or transportation systems the way heavy snow, freezing rain, or hail can. In fact, sleet is so light and tiny it usually bounces when it hits a hard surface.
Sleet is not the same as freezing rain. Freezing rain also falls through a cold layer of air close to the ground. However, the rain does not freeze until it touches the surface of an object. When you see trees coated in jackets of ice, you are seeing the results of freezing rain. The rain was liquid when it landed on the tree branch, then immediately froze solid.
Sleet also is not the same as hail. Hail, like sleet, is a collection of ice pellets. But hail forms in a cloud, while sleet forms as it falls. Hail freezes from the inside out, while sleet freezes from the outside in. Hail also tends to fall during thunderstorms in the spring and summer. Sleet usually falls in the winter.
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