Whiteout (weather) - AbsoluteAstronomy.com

Whiteout is a weather

Weather

Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...

condition in which visibility and contrast are severely reduced by snow

Snow

Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...

or sand. The horizon

Horizon

The horizon is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting...

disappears completely and there are no reference points at all, leaving the individual with a distorted orientation. Whiteout has been defined as: A condition of diffuse light when no shadows are cast, due to a continuous white cloud layer appearing to merge with the white snow surface. No surface irregularities of the snow are visible, but a dark object may be clearly seen. There is no visible horizon.

A whiteout may be due simply to extremely heavy snowfall rates as seen in lake effect conditions, or to other factors such as diffuse lighting from overcast cloud

Cloud

A cloud is a visible mass of liquid droplets or frozen crystals made of water and/or various chemicals suspended in the atmosphere above the surface of a planetary body. They are also known as aerosols. Clouds in Earth's atmosphere are studied in the cloud physics branch of meteorology...

s, mist

Mist

Mist is a phenomenon of small droplets 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...

or fog

Fog

Fog is a collection of water droplets or ice crystals suspended in the air at or near the Earth's surface. While fog is a type of stratus cloud, the term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated...

, or a background of snow. People can be lost in their own front yards during a true whiteout, when the door is only 10 feet away, and they would have to feel their way back. Motorists have to stop their cars where they are, as the road is impossible to see. Normal snowfalls and blizzard

Blizzard

A blizzard is a severe snowstorm characterized by strong winds. By definition, the difference between blizzard and a snowstorm is the strength of the wind. To be a blizzard, a snow storm must have winds in excess of with blowing or drifting snow which reduces visibility to 400 meters or ¼ mile or...

s, where snow is falling at 1 or 2 inches per hour, or where the relief visibility is not clear yet having a clear field of view for over 30 feet, are often incorrectly called whiteouts.

Types

There are four different forms of a whiteout:

In blizzard
Blizzard
A blizzard is a severe snowstorm characterized by strong winds. By definition, the difference between blizzard and a snowstorm is the strength of the wind. To be a blizzard, a snow storm must have winds in excess of with blowing or drifting snow which reduces visibility to 400 meters or ¼ mile or...

conditions, snow already on the ground can become windblown, reducing visibility to near zero.
In snowfall conditions, the volume of snow falling may obscure objects reducing visibility to near zero. This only happens during lake-effect snow, or mountain-effect snow, where the volume of snow can be many times greater than normal snows or blizzards.
In clear air conditions, when there is little or no snow falling, but the ground is completely covered with snow, diffuse lighting from overcast clouds may cause all surface definition to disappear. It becomes impossible to tell how far away the snowy surface is. In polar regions this optical illusion
Optical illusion
An optical illusion is characterized by visually perceived images that differ from objective reality. The information gathered by the eye is processed in the brain to give a perception that does not tally with a physical measurement of the stimulus source...

can make whole snow-covered mountain
Mountain
Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...

s invisible against the background white cloud, and the horizon
Horizon
The horizon is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting...

cannot be identified, slopes cannot be judged for steepness, and snow surfaces cannot be seen. This effect is exacerbated by a smooth surface of fresh snow. It is only when a contrasting object is placed on a snowy surface that the surface can be detected. In less extreme cases, it may suffice to break the snow surface by throwing a snowball ahead. This form is also known as flat light or sector whiteout.
Where ground-level thick fog exists in a snow-covered environment, especially on open areas devoid of features.

Hazards

Whiteout conditions pose threats to mountain climbers, skiers, aviation, and mobile ground traffic. Motorists, especially those on large high speed routes are also at risk. There have been many major multiple-vehicle collision

Multiple-vehicle collision

A multi-vehicle collision is a road traffic accident involving many vehicles. Generally occurring on high capacity and high speed routes such as freeways, they are one of the deadliest forms of traffic accidents...

s associated with whiteout conditions. One motorist may come to a complete stop when he or she cannot see the road, while the motorist behind is still moving.

Types

Hazards

See also