Illinois
6:30 am
Wed February 19, 2014

Boosting Your Winter Vocabulary

Graupel

Northern Illinois is experiencing a brief warm-up this week. But it still seems there is no end in sight to the brutal winter that has pummeled the region. Despite the inconveniences, the endless cycle of snow and cold temperatures has brought some seldom used weather terms to the surface.

Morning Edition version by Mike Moen

One of those terms is graupel. Amy Sealy, who’s with the National Weather Service in Romeoville, says they see it from time to time.

"You have a coating of ice around some snow. And usually it's under five millimeters in size, but it can be larger."

Graupel is often described as another version of hail. But it's not exactly the same thing. Graupel looks like little Styrofoam pellets that immediately fall apart when touched.

Graupel was reported during Monday's snowstorm. But weather experts say the term doesn't get thrown around much because it is often confused with sleet.

Meanwhile, Monday's snow event produced an even more semi-rare winter event: thunder snow.

"Similar to a thunderstorm in the spring or summer, you have a lot of upward moving air, and it usually produces much heavier bursts of snow," Sealy said.

And NIU meteorologist Gilbert Sebenste says like a traditional thunderstorm, thundersnow offers many of the same elements.

"You need to treat it like any thunderstorm. In other words, one can marvel at it, but you can't say you're not in danger of being hit by lightning." Sebenste said.

And if you're looking for something extremely rare that has popped up this winter, there are frost quakes.

"Frost quakes occur when you get a thaw, and water slips into cracks in the ground. Then, when you get a very rapid freeze, water expands," Sebenste said.

Sebenste says the ground then is forced to expand in explosive like fashion to handle the freezing water. But unlike an earthquake, there usually isn't any risk for serious damage.

Getting back to more familiar terms. Sebenste says the brief surge in temperatures, combined with the frozen ground, could create ideal conditions for flooding in the coming days. He says that melting snow is going to be looking for somewhere to go.

"It's not going to seep into the ground hardly at all, and so it's gonna make a run for the lowest possible spots that it possibly can." Sebenste said.

And forecasters also warn about the potential for ice jams along area rivers.

And once this weather spell ends, another round of frigid temperatures is expected, leaving many northern Illinois residents to wonder, when will this brutal winter and its seldom used terms come to an end?