Yes, it is pronounced how you think and this past weekend living here in BC I had the rare opportunity to gaze upon one of winter’s most beautiful tapestries, hoar frost (also known as hoarfrost, radiation frost, or pruina). It had consumed all of the surrounding trees; shrubs, lawns, logs and other assorted foliage for miles around and as the sun rose, the land glistened. A lot of people don’t recognize the phenomenon because in a number of places around the world it only occurs in conjunction with snowy conditions. This portrays the illusion that it is in fact snow that has fallen and stuck to all of the surfaces of a particular tree, telephone line or rooftop while in fact this is not the case. The name ‘hoar’ originates from an Old English term meaning “showing signs of age”, which in this context refers to the foliage it covers appearing as if it were all white hair.

This frost is typically created on clear nights that create an environment where heat radiates out to the sky faster that it can be replaced by warm air moved by the wind or surrounding warmer objects. This vacuum of cold air left is well below the frost point of surrounding air and even further below the freezing temperature of water. This effect is multiplied by frost flood or frost pocket; which is where cold air from the ground is pushed out and then flows downhill accumulating in hollows and valleys.

Next week we’ll continue on hoar frost, explaining the seriously dangerous application of these seemingly harmless icicles both for humans and what it means for plants.

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