Our springlike weather hit a speed bump this week with some cooler temperatures, windiness and even snow. This kind of weather flip, which sometimes happens this time of year, can create a rare meteorological phenomenon known as snow rollers. On March 31, 2009, they put North Idaho on the map.
That evening, a resident of Craigmont was driving home from work when he spotted a snowy field full of objects shaped like giant rolls of toilet paper. He snapped some photographs and forwarded them to the National Weather Service, which posted them on its website.
“Many of the snow rollers were about 18 inches tall in height, while the largest rollers were about 2 feet tall,” the weather service wrote.
If you try Googling “snow rollers” today, you’ll find the definition of the term posted on the agency’s web page, accompanied by those same photographs taken near Craigmont. The pictures – shot 12 years ago this month – have also been published by numerous news organizations, including the Washington Post.
Snow rollers are classified as rare by the weather service because conditions have to be precise for them to develop. They require the right combination of temperatures, terrain, snow and wind to form. Unlike building a snowman, no human touch is involved.
Here in the West, the most ideal mix of conditions seems to occur during the months of February and March: light, wet snow; temperatures near the melting point; and winds strong enough to push the snow chunks across flat terrain but not strong enough to blow them apart. Snow rollers can also form with the help of gravity, not wind, when small snow chunks roll down steep hills and mountain sides.
Whether formed in an open field or on a slope, they curl into signature hollow tubes as they move along the ground and pick up more snow. Once snow rollers come to a stop, they can be as small as an orange or as large as a 30-gallon drum.
Just a few weeks ago, these distinctive creations of nature made national news when scattered atop the front lawn of Utah State University in Brigham City. Their appearance came after a stretch of warm weather was followed by a cold front that brought snow and winds.
“The snow fell on a warm ground, which probably resulted in it becoming kind of a denser, wetter snow,” Brock Burghardt, a meteorologist for the National Weather Service in Utah, told the Associated Press. “The wind pushed it along and because the snow had melted, and it was a little more wet and dense, it snowballed on itself.”
Snow rollers are rare. They’re also fascinating. And if you’re lucky enough to spot them, they’re very photogenic – pull out your smart phone and snap away.
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