Rare weather event produces spontaneous snowballs
Assign to Google Classroom
Thousands of snowballs rolled in a flat central Idaho field look like the work of hundreds of go-getting kids. But there were no human tracks.
A rare weather event caused the spontaneous snowballs. They appeared at the Nature Conservancy's Silver Creek Preserve and surrounding fields. The area is near the tiny town of Picabo.
Sunny Healey is the preserve manager. She spotted the cylindrical shapes up to 18 inches high on Jan. 30. She saw them following an overnight windstorm. They created long lines in the snow as they moved.
"You could see the tracks that they made. And I thought that was really curious," Healey said. "I had to stop a couple times. Then, along Highway 20, there were thousands of them."
So-called snow rollers are rare. The exact weather conditions needed to form them are not defined, said Jay Breidenbach. He is a meteorologist with the National Weather Service. Snow rollers up to 18 inches are really rare.
"Those are some pretty big rollers," Breidenbach said. "I've seen some small rollers. But never that big."
In general, it takes an odd combination of a couple of inches of snow with the right water density and temperatures near freezing, followed by strong winds, he said.
"It can't be real dry snow or it would blow into drifts," Breidenbach said.
Rollers need some type of firmer base, such as a frozen layer of earlier snow, for the new powder to start rolling on. Plus, the wind must be strong and steady. But not with powerful gusts that could damage the formations.
"It would probably blow them apart because they are fragile," Breidenbach said.
It snowed on Jan. 29. The snow became wetter toward evening, Healey said. She lives at the preserve. She said the winds woke her up.
In her five years working at the preserve, she had never seen such an event. But a local rancher in his 70s told her he's spotted them twice.
"We know basically how they form and why they form. But we don't know the exact details," Breidenbach said. "It would be interesting to go there with some weather instruments to watch them form."
CRITICAL THINKING QUESTION
How did wind create the snowballs?
Write your answers in the comments section below