Thursday, January 12, 2012

Dippin’ Dots snow? Nope - that was graupel!

As advertised, a potent Arctic cold front swept through the Mid-South this morning, bringing much colder temperatures, strong wind gusts, and periods of snow flurries and light snow showers. As the snowflakes began falling in the metro area, several people took notice of the slightly unusual shape and characteristics of some of the “flakes.”  Some wondered if it was sleet, others likened the snow to Dippin’ Dots ice cream or "the stuff inside a beanbag" – which is a pretty accurate comparison! No, it wasn't ice cream falling from the sky (unfortunately!), but it does have a meteorological explanation.

Some of the snow you may have seen today is actually termed “graupel.” Graupel forms when snowflakes falling through the atmosphere collide with supercooled water droplets, or water droplets that maintain their liquid form even in temperatures below 32 degrees. Once these supercooled water droplets collide with a snowflake, a thin coating of ice instantly forms around the snowflake, turning it into a small, often irregularly-shaped ball of ice that may look similar to a sleet pellet or even small hail. Because of its similarity in appearance to sleet, graupel sometimes may be referred to as “snow pellets,” though graupel is not a form of sleet. With sleet, the original snowflake melts in a warm layer aloft, and then refreezes before reaching the ground. With graupel, the original snowflake never melts as ice coats it.

Also like sleet, as graupel hits the surface it may slightly bounce, though because it is softer than hail, it doesn't bounce as much! Due to its thin coating of ice, graupel is often very fragile, and can fall apart if touched or when coming into contact with a surface. Graupel, like ice and snow, can accumulate on roadways and cause slick conditions, but fortunately today’s snow and graupel was light and brief enough that no travel problems resulted, with any accumulations generally limited to a small dusting on grassy areas, cars, and rooftops.

Graupel in south Jonesboro, AR earlier today. Photo credit: Hunter Smith (@huntergsmith)

--Kevin Terry, MemphisWeather.Net

For weather information for Memphis and the Mid-South, where and when you need it, visit on the web, on your mobile phone, download our Android app, and visit us on Facebook or Twitter.

No comments: