What is graupel?

Graupel is defined as heavily rimed snow particles, which generally reach diameters of up to 5 mm. This formation occurs when supercooled water droplets in the atmosphere collide with snowflakes, causing them to accumulate layers of ice. The process results in soft, rounded pellets that are often described as looking like small, soft balls of snow or soft hail. Graupel can form during winter storms and in conditions where there is significant moisture in the air, allowing for effective rimming of the snowflakes.

Understanding graupel is important as it distinguishes itself from other forms of ice precipitation. For instance, the other options reference different phenomena that do not align with the characteristics of graupel. Small ice particles from frozen rain would not have the rime formation associated with graupel. Regular snowflakes are simply the classic precipitation form and do not involve the rime process that produces graupel. Lastly, liquid drops that freeze while descending typically refer to sleet or ice pellets, which also differ from the structure and formation process of graupel. Thus, recognizing the unique features of graupel helps in identifying and classifying different types of winter precipitation.