Photo by: by John Dixon

A snow roller sits along U.S. 45 between Urbana and Thomasboro on Wednesday.

CHAMPAIGN - No, all those large snowballs that showed up throughout the area Wednesday morning weren't put in place by leprechauns.

A meteorologist at the Midwestern Reginal Climate Center at the Illinois State Water Survey says the snowballs were a rare natural phenomenon called snow rollers.

"I've seen pictures of snow rollers before, but Wednesday was the first time I've ever seen them in person," Steve Hilberg said. "It doesn't happen very often around here."

Hilberg said snow rollers are caused by a rare combination of snow consistency, temperature and high winds.

"Snow rollers happen when snow is rolled up by the wind," Hilberg said. "It's not unlike a kid trying to make a big snowball for a snowman. Only this time the wind serves as the kid."

Weather conditions began to set the stage for the snow rollers to appear Tuesday night, according to Hilberg, when temperatures climbed above freezing.

"The warm weather made the snow around here wetter, and snow always packs better when it is wet," he said.

Then more snow began to fall on Wednesday, temperatures dropped just below freezing, and that snow was picked up by 35- to 40-mph winds, Hilberg said.

"The wind just picks up the snow as it rolls along the ground, and you get almost a jellyroll effect," Hilberg said. "Some of this snow began to look like jellyrolls in open areas. In other places, the wind rolls up snow balls."

If the snow had been less wet or if the wind had been lighter, there wouldn't be enough force to form the snow rollers, according to Hilberg.

"You really need a snow wind of at least 35 miles per hour with a frontal system for this to happen," he said.

Hilberg said temperatures have to be just below freezing for snow blowers to occur.

"Had the temperatures been down to the low 20s or colder, we would have a lot of blowing snow," he said.

According to Hilberg, the phenomenon is more common in northern states like Michigan, Wisconsin and Minnesota.

"They've got snow on the ground for most of the winter, so there are more opportunities for snow rollers to occur there," he said.