Icy precipitation is a type of weather phenomenon that occurs when temperatures are low enough for water droplets to freeze in the atmosphere. The two most common forms of icy precipitation are HAIL and SLEET. HAIL is composed of frozen raindrops or ice pellets that are larger than 5 millimeters in diameter and fall from cumulonimbus clouds. SLEET is a combination of snow and rain, and is composed of small ice pellets that are less than 5 millimeters in diameter.