Michal King was in awe at the frosty scene he saw on the roof across the street, “as if a giant paintbrush had been at work during the night.”
Yes, Mother Nature is quite an artist.
When it comes to the marvels of weather, it can be a little like baking a cake: you need all the right ingredients for things to turn out! Hours before Michal snapped the photo, a cloudless sky, windless night and relatively high humidity came together to produce hoar frost on that church hall roof in Dartmouth, N.S. A few hours after sunrise, the shadow of the leafless tree had prevented the sun from melting off the hoar frost!
Hoar frost. It doesn’t sound pretty but that’s what it was. Hoar frost is a deposit of ice crystals on objects – most often vegetation – exposed to the air. It’s formed by direct condensation of water vapour to ice. The key for hoar frost to form is there must be an influx of moisture into the region while the air remains sufficiently cold. You’re no doubt familiar with the term “dew point.” In the warmer months, it’s the temperature to which an air mass must be cooled to reach its condensation point. Frost point is its winter cousin and results in hoar frost.
Hoar frost can be so thick that it can look like snow. Hoar frost shouldn’t be confused with rime, which occurs when freezing fog forms a solid layer of ice. This might help: from gas to solid, it’s hoar frost; from liquid to solid, it’s rime.
People often ask me where the term comes from. The adjective “hoar” or “har” goes back to Old English and means “greyish white; grey or grey-haired with age.”
Hoar frost is very photogenic! Thanks Michal.
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