That's how they roll: 'nature's snowballs' spotted in Ottawa
Seeing 'snow rollers' form an ultra-rare winter treat, senior climatologist says
Round bales of windswept snow that appeared in front of the Supreme Court in downtown Ottawa Thursday are a rare winter treat, according to David Phillips, a senior climatologist at Environment Canada.
I've never really heard of any eyewitnesses to snow rollers.- David Phillips, Environment Canada
Seeing the "snow rollers" actually form is rarer still, Phillips said.
"I've never really heard of any eyewitnesses to snow rollers," Phillips said."I've heard of them forming in fields outside of small towns, and people sort of stumble upon them. Because they really are nature's snowballs."
Sheila Nemcsok was passing by the Supreme Court Thursday when she witnessed the unusual phenomenon, and managed to not only snap a few pictures, but capture the event on video.
A variety of factors need to occur in precise order for snow rollers to form, said Phillips. They include freshly fallen snow which lands on, but doesn't stick to, a crusted surface while the temperature is three or four degrees above freezing — warm enough to begin melting the snow, but not to melt it altogether.
Conditions 'absolutely perfect'
Then there needs to be a wind of at least 45 km/h to whip the snow into shape. In this case, it appears strong downward gusts acted as the "trigger" to get the snow rolling, Phillips said.
"Conditions need to be nearly perfect for snow rollers to form," he said. "And to form downtown, in a major city in Canada, I mean, it really is a head-shaker."
Phillips was so incredulous he verified the weather conditions at the time the video was taken, and proclaimed them "absolutely perfect for snow rollers to occur."