Sepia tinted color/colour photograph by J. McCombie. Frost, snow and mist cover the winter woods and farmer’s field.
Frost is the solid deposition of water vapor from humid air. It is formed when the temperature of a solid surface is below the freezing point of water and also below the frost point. The size of frost crystals varies depending on the time they have been building up and the amount of water vapour available. Frost crystals are translucent, but scatter light in many directions, so that a coating of frost appears white. There are many types of frost, such as radiation and window frost. Frost may damage crops or reduce future crop yields, hence farmers may take measures to prevent it forming.
Hoar frost may have different names depending on where it forms. For example, air hoar is a deposit of hoar frost on objects above the surface, such as tree branches, plant stems, wires; surface hoar is formed by fernlike ice crystals directly deposited on snow, ice or already frozen surfaces; crevasse hoar consists of crystals that form in glacial crevasses where water vapour can accumulate under calm weather conditions; depth hoar refers to cup shaped, faceted crystals formed within dry snow, beneath the surface.
Snow is precipitation in the form of flakes of crystalline water ice that falls from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless subjected to external pressure. Snowflakes come in a variety of sizes and shapes. Types that fall in the form of a ball due to melting and refreezing, rather than a flake, are known as hail, ice pellets or snow grains.
Mist is a phenomenon caused by small droplets of water suspended in air. It can occur as part of natural weather or volcanic activity, and is common in cold air above warmer water, in exhaled air in the cold, and in a steam room of a sauna. It can also be created artificially with aerosol canisters if the humidity conditions are right.