Graupel Isn't Snow, Nor Sleet, Nor Hail, So What the Heck Is It?

If you inhabit a place where snow falls a lot, then odds are that you've heard more than one name for this type of precipitation; that frozen stuff is not only called "snow," but it turns out that there are many nuanced forms of the words "snow" and "snow crystal."

In Scotland, where it snows for about 60 days a year in the highlands, there are 421 commonly known words and phrases used to describe snow crystals. These words range from flindrikin, which means a "slight snow shower," to snaw-pouther, which describes a "fine but driving snow." The Scots clearly aren't lumping all their snowfall into one category.

Neither are many other cultures, including the Inuit people who inhabit Arctic regions of Alaska, Greenland, Canada and Siberia. In the Inuit language there are more than 50 words for snow pellets and snow-adjacent precipitation, such as graupel. In the Inuit dialect spoken primarily in Canada's Nunavik region, "matsaaruti" is the word used to describe wet snow pellets, while "pukak" refers to a crystalline powder snow that has the grainy consistency of salt.

What Is Graupel?

But what happens when Mother Nature serves up a precipitation combo of supercooled water droplets we don't know what to call? Enter: Graupel, which The Washington Post calls "the wintry precipitation you've never heard of" and Merriam-Webster calls "pearl barley."

Graupel is actually an interesting mix of snow crystals and ice, no matter what Merriam-Webster calls it. Graupel should not be confused with sleet, which is sturdier and more frozen; graupel occurs when a snow pellet falls and is encapsulated by ice. Sounds like hail, right? Well, it isn't hail. Not exactly.

Hail is formed from raindrops that are lifted upward into freezing air by wind drafts. Frozen hailstones can start as small as single raindrops that fall, but as the process continues, they grow in size and dimension as more and more rain freezes to the hailstone. Once the frozen raindrop becomes too heavy for the updrafts moving in the freezing upper atmosphere, soft hail is created and the hailstone falls earthward. Hail usually occurs during severe weather.

Graupel, on the other hand, can be — but doesn't have to be — associated with severe weather. While graupel can be seen in weather that creates supercooled water droplets, graupel doesn't necessarily mean nasty atmospheric conditions. In order to form, all graupel needs is cold, winter-like temperatures.

Graupel begins as individual snowflakes formed in the upper atmosphere. The snowflakes then fall through a layer of supercooled liquid droplets, which causes the raindrops to "rime," or instantly freeze onto the snow crystals at temperatures of 32 degrees Fahrenheit (-17 degrees Celsius) or lower. The end result is graupel: Graupel is tiny, white pellets that resemble small hail but which, unlike hail, remain soft and crushable.

Where Does the Word 'Graupel' Come From?

Graupel, in general, has the appearance of riced cauliflower and this gives us a clue as to the origin of the precipitation's name, "graupel." The word graupel first appeared in the Germanic languages and is derived from "graupe," which is the word for pearl barley. The word graupel's first known association with grainy falling snowflakes, pellets or soft hail, was in 1889 when a weather report used it to describe rimed snow crystal pellets. In modern use, the word "graupel" has become a synonym for "soft hail."

The most important criteria of rime is that it is comprised of supercooled rain that freezes and attaches to an exposed surface during winter storms. When that exposed surface is a snowflake, this rime creates graupel, but that's not the only condition in which raindrops freeze around an object at its core, creating ice pellets. This type of freezing process can encapsulate many objects, including trees and branches, resulting in a winter wonderland full of glittery surfaces.

Depending on how these frozen surfaces are coated, however, it may not be rime that's responsible at all — but the hoar frost that forms. Hoar frost has a similar look to rime, but skips the supercooled droplets stage of formation. It goes straight to crystallizing into ice pellets, forming fragile frozen droplets on just about anything it encounters during low-to-the-ground freezing temperatures: grasses, leaves, branches and even the occasional unfortunate spider.

Frequently Asked Questions

What safety precautions should I take during graupel precipitation?

During graupel precipitation, it's important to treat surfaces as potentially slippery, much like during sleet or light snowfall. Use caution when walking or driving, as graupel can create slick conditions, and visibility may be reduced due to the falling pellets.

What's the difference between hail and graupel?

Hail consists of hard, solid balls of ice that form in strong thunderstorm updrafts, growing as they ascend and descend repeatedly, collecting layers of ice. Graupel is softer and forms when snowflakes collect and freeze supercooled water droplets, resulting in small, frosty pellets.