Most of us are familiar with the usual winter suspects: snow, sleet, freezing rain and ice. But what in the world is graupel?
Graupel starts as snow, but its final form is a slushy pellet.
As snowflakes encounter supercooled water droplets, ice crystals form instantly on the outside of the snow. In a process called accretion, these ice crystals will form one on top of the other until the snowflake is completely encased in a rime coating.
Typically, graupel pellets have a diameter of less than five millimeters, but they can be as large as a quarter.
It is easy to confuse graupel with sleet or hail. Look closely at the pellets and you will find a subtle difference. Sleet pellets and hailstones are hard all the way to the center and they will bounce when they fall to the ground. Graupel is much softer. It usually falls apart when touched.