frost

How does hoar frost form? theWeather Club Wed, 30/11/2016 - 10:11

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.  

What causes these beautiful frost patterns?

Clear nights and plunging temperatures can deposit a thick frost by daybreak. For frost to form, the temperature of the surface must be below 0°C. But what causes these pretty, leaf-like patterns? The patterns are the result of very tiny imperfections on the glass, such as scratches, specks of dust and salt, or the residue from washer fluid. These variations in the surface affect the way that the ice crystals form and branch out, forming the beautiful patterns captured in this image, taken in North Yorkshire on an smartphone by Paula Davies.