Sleet is a form of precipitation in which raindrops or melted snow refreeze into small ice pellets before reaching the ground.
For sleet to form, the atmosphere usually contains a warm layer aloft that melts falling snow, followed by a sufficiently deep subfreezing layer near the surface. The melted drops refreeze in that lower cold air and arrive as hard pellets. In the United States, this precipitation is commonly called ice pellets; in the United Kingdom, “sleet” can also describe a mixture of rain and snow.
Sleet differs from freezing rain, which remains liquid until it hits a cold surface and then freezes into glaze ice. It also differs from hail, which grows inside thunderstorms through repeated upward movement.
Sleet can make roads and pavements slippery, but it generally produces less continuous coating than freezing rain. Forecasts distinguish these forms because their hazards and required travel precautions differ.