Over the weekend, the city of Calgary’s trees put on a show to welcome the new year. This natural phenomenon produces glittering frost in the city’s many green spaces. But it’s not snow that’s doing it — it’s called “hoarfrost.”
Hoarfrost, a freezing effect that leads to some especially beautiful photographs in the dead of winter, occurs under clear skies and cold temperatures, when the moisture in the air skips the liquid phase and goes straight from a gaseous to a solid state. The water vapour in the air sticks to the trees, creating a picturesque, frosty coating.
Hoarfrost is fluffy in nature, but when the particles look more like droplets, it can be a little more dangerous. Rime ice forms in low cloud, foggy conditions, where there are lots of moisture particles in the air. When those liquid drops hit trees or other solid objects, they freeze immediately. Rime ice develops quickly, and the sheer weight of it can cause power outages and even bring down airplanes.
Its lighter cousin, hoarfrost, is significantly daintier. It’s a rare natural phenomenon, but when it hits the city, it turns our metropolis into an icy world of wonder.
Here’s what else to know about hoarfrost.
More than just snow
The light dusting of frost on Calgary’s native trees is beautiful, and it has a scientific explanation. Hoarfrost is a deposit of ice crystals on objects that are exposed to cold air. It’s a natural phenomenon that’s common on the prairies of Canada, where winter cold snaps can be a weekly, even daily occurrence.
Over the Jan. 2 to 4 weekend, many Calgarians noticed the effect settle over the city, and it was the subject of photographs and pontificating. Though some refer to this frosted look as simply “snow,” it’s something else entirely.
There are differences between hoarfrost and rime ice, and you should know them as they could one day save your life. While hoarfrost creates a fluffy, light coating that can be easily brushed off, rime ice freezes to surfaces, creating a “dripping” effect that can weigh down infrastructure and cause serious problems. High-humidity, frosty mornings can also create extra slick conditions on the road, so you should take extra care when driving.

Calgarians woke up to an especially exquisite display of hoarfrost over the weekend, and many captured its beauty in photographs and videos shared to social media.
The conditions should continue into the week, allowing for more hoarfrost and more opportunities to snap a photo of this wintery display. If you get out there yourself with a camera, just be sure to bundle up — and don’t forget about the differences between hoarfrost and rime ice going forward.
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