Graupel: Hail *imposter* covers Sturgis, Spearfish in early October
Reports poured in over the last week of hail falling in places like Sturgis and Spearfish, except that not all of the frozen precipitation was actually hail.
The hail reports, however, came in with less confidence as residents found the hail to be… lacking. The hail disintegrated as it was picked up, and didn’t have the characteristic sharp *tap* on cars and windows.
That’s because many of these residents were actually experiencing graupel. This can also be called snow pellets or soft hail.
The soft, tiny, snow-ball like consistency is classic for convective showers in the Black Hills in the Spring and the Fall. When temperatures aloft are very cold liquid water becomes supercooled, meaning that it stays liquid at temperatures below freezing.
When water is supercooled, all it needs is a little disturbance to instantly freeze. That disturbance comes in the form of ice crystals that exist along side the supercooled water. The supercooled water freezes around the ice crystals in a process called riming.
The main difference between graupel and sleet is that sleet falls as a liquid and freezes before it hits the ground, and graupel is frozen precipitation that collects supercooled liquid water as it falls.
Over the next few months, we’ll likely experience more cases of graupel, along with all the other fun icy things that fall from the sky. Winter is around the corner!