Winter precipitation can take many forms. We’re familiar with snow and freezing rain, of course. But what about sleet? Snow grains? Graupel? Sleet is a common term for ice pellets. These are frozen raindrops or refrozen melted snowflakes. Sleet is generally transparent or translucent and 5 millimeters or less in diameter. It bounces when hitting hard ground and makes a sound on impact. It differs from small hail in that there are no layers, as are found when ice builds up on a hailstone. Other unusual forms include snow grains – small opaque white particles of ice that don’t shatter or bounce when they hit the ground, and snow pellets, or graupel, which have a snow-like structure and generally bounce or break apart when it hits the ground.
Mary Knapp, Weather Data Library