On more than one occasion last fall, my husband and I watched players and sports reporters alike grappling with the precipitation that was occurring before or during the Cleveland Browns football game. The FirstEnergy Stadium, home of the Browns, is located on the southern shore of Lake Erie and is no stranger to wild weather. News reporters struggled to identify the precipitation type…sleet? Snow? Freezing rain? Hail? All good guesses, but the correct answer was actually graupel…which many meteorologists on Twitter were quick to point out.
So…what is graupel?
Essentially, the National Weather Service defines graupel as snow pellets or small hail. So the reporters weren’t that far off…and who can blame them? Washington Post has even called graupel “the wintry precipitation you’ve never heard of.”
What makes graupel so special?
That’s a good question, and to fully understand the answer, we should refresh ourselves on different precipitation types. We’ve talked before about how all wintry precipitation (even rain!) actually begins as snow, or ice crystals, high in the atmosphere. The air temperatures between the upper atmosphere and the surface have a huge impact on the type of precipitation that falls. Snow and rain are easy enough to understand – the air temperature either remains below freezing between the atmosphere and the ground (allowing the snow to fall to the ground as pure snow), or it encounters warm air and the air temperature remains above freezing all the way to the surface (melting the snow and producing rain).
That leaves us with sleet and freezing rain, which are commonly confused…but their impacts are widely different! Sleet are ice pellets which encounter a shallow layer of warm air, allowing them to melt partially, before falling through a deeper layer of air with temperatures that are below freezing. This journey means that sleet completely refreezes before reaching the surface and will then bounce on contact with surfaces, resulting in minimal impacts.
The biggest trouble-maker in winter precipitation is freezing rain, snowflakes that have encountered a deeper layer of temperatures above freezing, allowing them to melt into a liquid. Temperatures below freezing at or near the surface allow the precipitation to freeze on contact with surfaces, wreaking havoc. Ice accumulation on roadways, sidewalks, powerlines, trees, and more can have huge impacts on travel, infrastructure, and health.
The thing that makes graupel unique is the way in which it forms. Snowflakes falling from the sky pick up an extra layer of moisture on their way down to the surface, and supercooled droplets stick to the crystals. This changes the typical appearance of snowflakes in such a way that it almost resembles small balls of Styrofoam….explaining why many mistake it for hail! The difference between the two, though, is their strength. Hail is typically hard, while graupel actually disintegrates easily when touching it (because there is snow, not ice, inside!).
Though I’ve never experienced graupel, I think it would be cool! Statistics on graupel are also not readily available, one news station in Colorado believes that it occurs more often there than in other places. Have you ever experienced it? Comment and let us know!