It's rare, but with just the right conditions Mother Nature can roll her own snowballs. That's basically what happened with Wednesday's snowstorm in Warren County and the Slate Belt.

The phenomenon is called a snow roller. It appears as a cylindrical snow mass pushed along by wind.

Lehighvalleylive.com freelance photographer Rich Maxwell estimated there were hundreds of them in farm fields off Garrison Road in Harmony Township on Thursday.

Snow rollers were also seen in the fields off Martins Creek-Belvidere Highway in Lower Mount Bethel Township. "The beauty of living in the area that we do," Slate Belt Regional police said in a Facebook post sharing a resident's photos.

The beauty of living in the area that we do.... Shared by Angela Cooper: My husband sent me these pictures from along the flats of Belvidere-Martins Creek Hwy. We call these Snowman Seeds. Posted by Slate Belt Regional Police Department on Thursday, March 22, 2018

Precise conditions are necessary for snow rollers to form. The American Meteorologial Society defines them as:

"It occurs when snow, moist enough to be cohesive, is picked up by wind blowing down a slope and rolled onward and downward until it either becomes too large or the ground levels off too much for the wind to propel it farther. Snow rollers vary in size from very small cylinders to some as large as 1.5 meters long and more than 2 meters in circumference."

In a February report on snow rollers found in Canada, National Geographic described the exact set conditions they require:

"There must be a light dusting of snow on top of an icy layer on the ground, often on a hill or other expanse with no protruding vegetation. The dusting needs to be just wet enough so that it can adhere to itself but not stick to the ground. The wind must be around 30 miles per hour to coax the snow into its cylindrical shape, and the temperature must be three to five degrees above freezing. This level of cold allows for the rolling snow to form these fun shapes, but it doesn't let the snow melt completely."

The National Weather Service office in Mount Holly, New Jersey, said that there have been a couple reports of snow rollers in the region in the last few years. But they are by no means a common event.

Steve Novak may be reached at snovak@lehighvalleylive.com. Follow him on Twitter @type2supernovak and Facebook. Find lehighvalleylive.com on Facebook.