Fencycles at Gladfield on Thursday.
Fencycles at Gladfield on Thursday.

Various types of frost

FROST is the freezing of water vapour from the atmosphere. It forms when the temperature goes below zero at ground level.

The amount of frost depends on how long during the night the ground has been freezing and how much humidity is in the atmosphere.

Because of its crystalline structure, it scatters the light in many directions and this is why it appears to be white to us even though each crystal is translucent.

Frost has many forms and even a slight breeze can affect the shape of the crystals. It can cause a phenomenon know as "frost arrows" with the crystals pointing one way.

Other terms are:

Black frost

This occurs when the dew point is too low, meaning there is no moisture for dew to form and freeze. It is called a black frost because it is not visible but once it warms a bit all the plants will turn black and die.

Hoar frost

This refers to the white frosts we see. Frost is loosely deposited on the ground or exposed objects and it forms on cold, clear nights when heat is lost into the open sky causing objects to become colder than the surrounding air.

Wind frost

This can occur when tiny ice crystals form due to very cold winds blowing over leaves, branches etc. It is the edging you may see on the leaves. We do not experience wind frost very often.

Fern frost or ice flowers

These form when glass is exposed to very cold air. The glass can change the shape of frost crystals causing fernlike patterns on the glass. It can also happen on clean, high-gloss, painted surfaces such as a new car. Look at a car yard on a frosty morning and you will see fern frost.

Other forms that are not seen in our region are white frost and rime frost.

GLASS MEETS ICE: Fern frost on the bonnet of a new car.
GLASS MEETS ICE: Fern frost on the bonnet of a new car. Terry West


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