What is Graupel?
Some people who live in snowy regions may notice two different types of snow during the winter storm season. One is the familiar crystalline snowflake, which falls from the sky and packs tightly on the ground. Another form of frozen precipitation, however, often falls during very cold weather, and has the consistency of small pellets. This type of snow is known as graupel, also called soft hail by meteorologists. While graupel has the appearance of white snow pellets, its formation is closer to that of hailstones. Winter storm clouds often contain water droplets which have cooled far below 32 degrees Fahrenheit or 0 degrees Celsius without turning to ice. Sometimes those supercooled droplets contact dust particles or ice crystals and form solid hail. Other times, the supercooled droplets attach themselves to snowflakes and freeze instantly. The air currents within the storm clouds continue to push the ice-covered snow flakes through supercooled water until they become too heavy and fal
The formation of graupel is very similar to that of hail, which is why graupel is also known as “soft hail.” Both hailstones and graupel grow in size through a process called riming – supercooled water droplets and ice crystals freeze or stick to the initial hailstone as it rises and falls within a cloud. Hail tends to be associated with warm-season (spring, summer, even fall) thunderstorms. The more vigorous updrafts associated with warm-season storms helps to keep a hailstone in the cloud longer, allowing it to grow to a larger size (technically, hail is considered to be a dense ice pellet at least 5 millimeters in diameter). A hailstone can have concentric layers (like when you slice an onion down the middle) of hard and soft ice, depending on the temperature of the hailstone at the time the layer formed. Graupel tends to be smaller (typically less than 5 millimeters) and is usually produced in cold-season storms. Less vigorous updrafts limit the size to which the ice can grow and t
