Frost is a component of winter weather that is often mentioned in poetry and stories. Jack Frost turns up in many fairy tales painting pretty pictures on windows and coating the world with silvery outlines.
There are several different forms of frost. All of them materialize when solid surfaces, like windows, are cooled to below the dew point of the air. It is the deposit left from saturated air.
The frost crystals’ size depends on time and the amount of water vapor. They are formed of speckles of ice which grow out from a surface.
Frost will dissipate quickly when exposure to sunlight brings the surface it covers above the melting point of water. This is easily observed as sunshine hits a thin covering of frost on grass.
There are three main types of frost: Hoar Frost, Rime Frost and Fern Frost.
Hoar frost is the frost you scrape off the windows of your car. It is the silvery white coating on the lawn which melts quickly once the sun shines on it. It occurs when air moisture touches a very cold surface and freezes instantly.
There are several different types of hoar frost:
Air hoar refers to hoar frost that forms on trees, shrubs, wires and fences above ground level.
Surface hoar is hoar frost that is deposited on already frozen surfaces like snow or ice. This can be a contributing factor in the formation of avalanches.
Crevasse hoar is a hoar frost that forms in glaciers.
Rime frost occurs quickly, usually during a well saturated air and windy weather event. This frost forms in an icy solid coating rather than the feathery appearance of hoar frost. It usually forms on an already wet surface before freezing such as a damp, icy wind blowing over a ships rigging.
Fern Frost is also referred to as window frost. This frost forms when very cold air collects outside a glass window with warm rather moist air on the inside. This usually occurs on single pane windows. It begins with tiny dew drops freezing and as more continue to form and freeze a delicate fern like pattern develops.
Two other type of frost worth mentioning are Advection frost and Frost flowers.
Advection frost also called wind frost occurs when a very cold wind blows over tree branches and deposits tiny ice spikes. These appear on the side against the wind.
Frost flowers occur when a freezing weather event happens and the ground is not frozen. Plant stems split and fluid comes out, and then freezes when it hits the air. Sometimes this can form into delicate and rare ice flowers.
Jack Frost does indeed paint the world with a delicate silvery brush, just as the story book tales depict.