How does hoar frost form?

How does hoar frost form?

Wed, 30/11/2016 - 10:11
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Under clear, cold nights in winter, a hoar frost can form.

A hoar frost forms in a similar process to that of dew; the difference being that ice crystals are deposited, as opposed to water, because the temperature of the surface is below freezing.

Hoar frosts most commonly attach themselves to the branches of trees, leaves and grasses, but can also be seen on objects such as gates and flowerpots. Sometimes the deposits can be so thick that it may even look like a dusting of snow has fallen, creating a typical winter wonderland day.  

Photo credit: Freezing fog and hoar frost by Andrew Bailey; 3rd place in the over 16s category of the RMetS/RPS Weather Photographer of the Year 2016 competition.

"The photo was taken in February 2016 during a cold spell of weather. Based on the forecast I left home at 4:30am to travel to north Suffolk to Herringfleet Mill; a location I had not visited before. At the mill the temperature was -4°C with freezing fog making for very atmospheric conditions. I particularly like the way this photo captures the sun burning through the mist, with the reed beds covered in white hoar frost and the mill shrouded in mist.”