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What in the world is graupel?

It's not hail and it's not snow... it's called graupel. A coating of rime ice overtakes a snowflake to form these tiny snowballs.

COLORADO, USA — Reports of tiny snowballs resembling hail have been coming into the 9NEWS weather center for the past two days.

It looks like Dippin’ Dots falling from the sky. Or an explosion of Styrofoam packing pellets. But this form of wintery precipitation is actually called graupel.

It forms in convective storms, like thunderstorms. You will usually hear thunder when graupel is falling.

Several lightning bolts flashed near Georgetown Monday as about an inch of graupel fell before turning to snow.

Graupel starts out as a snowflake, which forms very high in the cloud. It then falls through a layer of tiny supercooled water droplets. That means the water is below freezing but still in liquid form.

Those supercooled droplets freeze on contact with the flake forming a thin coating of rime ice around the flakes. The same rime ice coating gets deposited on things like conifer needles during a freezing fog event.

Credit: KUSA
Rime ice clinging to trees after a freezing fog

Graupel forms in all thunderstorms but usually melts into rain before it hits the ground. That’s why you usually only see it at the beginning or the end of thunderstorm season.

You will sometimes hear it called soft hail or snow pellets, but it is neither hail nor snow. It's kind of a combination of the two. It's ice-covered snow, but it is too small and soft to cause any damage.

We don’t keep graupel stats but it is a lot more common in Colorado compared to most states.

And, by the way, it’s spelled G R A U P E L, so don’t let your smartphone autocorrect the word when you’re trying to impress your friends from Texas with a cool twitter post.

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