Cumulonimbus is composed of water droplets and, especially in its upper portion, ice crystals. It also contains large raindrops and, often, snowflakes, snow pellets or hailstones. The water droplets and raindrops may be substantially supercooled.
The text enclosed in grey-shaded boxes, like this example, comprises Annex I to the Technical Regulations (WMO-No. 49) and has the legal status of standard practices and procedures.