Hoar Frost by the River
20 November
Apart from a small line of flying Canada Geese and a pair of Mallards on the water (can you see them), today’s WOW pictures are just to share the beautiful hoar frost we woke to at dawn. We don’t often see hoar frost hereabouts, once or twice a year at best, so it was worth grabbing the camera and heading down to the river … even before having the obligatory morning cup of tea, something that is exceptionally rare.
Hoar frost is a type of feathery frost that forms as a result of specific climatic conditions. The word ‘hoar’ comes from old English and refers to the old age appearance of the frost: the way the ice crystals form makes it look like white hair or a beard. To form, it requires slightly different conditions to “regular” frost. It forms when the water vapour in the air comes into contact with solid surfaces that are already below freezing point. Ice crystals form immediately, and the ice continues to grow as more water vapour is frozen. On a still night, it can grow well on tree branches, where the surface temperature is unlikely to rise above zero for several hours. The size of the frost that forms depends on how much water vapour is available to ‘feed’ the ice crystals as they grow. Hoar frost has a distinctive appearance as it forms hair-like or feathery structures as it grows.
Magic!
Thanks for the explanation about why it's called hoar frost. We had it in Ottawa too this morning.