Winter wonder: mystery snowballs show up on ponds
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CHARLO — A winter phenomenon called snow rollers have been cropping up on local ponds, drawing curious onlookers to wonder how these natural snowballs were created.
Snow rollers form when a light layer of snow falls atop ice; the wind picks up the layer and literally rolls the snow up across the surface into “round bale” shapes.
Snow rollers take just the right combination of ingredients, according to Marty Whitmore of the NOAA weather forecast office in Missoula.
“First you have to have snow that will pack together well … This is just like good snowball fight snow or snowman snow,” he said. “But you want it to be a fairly thin layer of new snow that doesn’t stick to snow below it. Otherwise the gathering snow would quickly become too heavy to move.”
Second, you need something to push the snow, such as gravity or wind.
“In the case of wind, you want enough to get a ‘wheel’ forming, but not so much it tears it apart after limited growth,” Whitmore added.
While some snow rollers are tube-shaped, the rollers on ponds southwest of Charlo look more like snow-covered rocks of varying sizes.
