An interesting weather phenomenon I’ve yet to encounter.
Those giant snowballs that seem to roll themselves are a rare weather phenomenon called snow rollers, meteorologist Don Day says. Basically, wind and gravity roll them up the same way you would when making a snowman.
By Greg Johnson
There’s nothing magic or mystical about those mysterious snowballs that sometimes seem to roll themselves. It’s science.
They’re called snow rollers, and can happen this time of year and near the end of winter when snowfall is the wettest and heaviest, said Cowboy State Daily meteorologist Don Day.
“They do happen here in Wyoming,” he said. “I’ve received emails over the last two winters from people who have experienced snow rollers in the Laramie area.”
Snow rollers form the same way many people make snowmen, by simply rolling along, picking up more snow as they go, growing larger and larger, Day said. If they get started on a slope, then gravity can take over and the snow rollers can get pretty large.
Leeanna McLean of The Weather Network reports that some snow rollers have reportedly been as large as a car.
“That’s why you can get some bigger snow rollers going down a steep slope,” Day added. “They can get really big.”
Even so, Day said he’s not aware of anyone being in the wrong place at the wrong time to be obliterated by an out-of-control snow roller.
“I haven’t heard of anything like that, but you never know,” he said. “As we see with the Daily Darwin, people find pretty ingenious ways to off themselves.”
Making Of A Snow Roller
Most of the time, snow rollers resemble round bales of hay dotting a field, and conditions have to be just right for the rare phenomenon to happen, McLean reports:
• The surface must be wet, loose and relatively thin.
• The layer below must be dry snow or ice that will detach easily from the top layer.
• The wind has to be strong enough to move the roller, but not so strong to break it up.
• It helps to be on a slope so the roller can be moved along by momentum.
Most of the time, something drops into the snow to get a snow roller started, Day said.
“Imagine those late-season snows, and it’s a really sticky snow,” he said. “Then the wind picks up and snow will fall off a tree in a little clump, or it will blow off a tree or a fence. Then the wind takes over and the little snowball gets moving.”
Snow rollers also usually won’t last very long, Day said. Although they can grow large, they’re also pretty fragile and melt easily.
Snow rollers also could be a more scientific explanation for how “Frosty the Snowman” can keep coming back to life after repeatedly melting, Day said. The classic holiday story says a magic hat does the trick, but snow rollers could be an alternate theory.
Like Frosty, seeing a snow roller around Wyoming is rare and seasonal, he said.