Whiteout (weather)

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Whiteout in Saskatchewan (March 2007) Pole line (413157823).jpg
Whiteout in Saskatchewan (March 2007)
Whiteout snow squall northwest of Waterloo, Ontario, Canada (February 27, 2014)
Relatively large, stationary whiteout on Lyell Icefield that lasted 4 hours Whiteout to clear, Mt. Lyell and its icefield.jpg
Relatively large, stationary whiteout on Lyell Icefield that lasted 4 hours

Whiteout, white-out, [1] or milky weather [2] is a weather condition in which the contours and landmarks in a snow-covered zone become almost indistinguishable. [1] It could be also applied when visibility and contours are greatly reduced by sand. The horizon disappears from view while the sky and landscape appear featureless, leaving no points of visual reference by which to navigate; there is absence of shadows because the light arrives in equal measure from all possible directions. [1] 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." [3]

Contents

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 clouds, mist or fog, or a background of snow. A person traveling in a true whiteout is at significant risk of becoming completely disoriented and losing their way, even in familiar surroundings. Motorists typically have to stop their cars where they are, as the road is impossible to see. Normal snowfalls and blizzards, where snow is falling at 3 or 5 centimeters per hour (1 or 2 in/h), or where the relief visibility is not clear yet having a clear field of view for over 9 meters (30 ft), are often incorrectly called whiteouts.

Types

There are three different forms of a whiteout:

  1. In blizzard conditions, snow already on the ground can become windblown, reducing visibility to near zero.
  2. In snowfall conditions, the volume of snow falling may obscure objects reducing visibility to near zero. An example of this is during lake-effect snow or mountain-effect snow, where the volume of snow can be many times greater than normal snows or blizzards.
  3. Where ground-level thick fog exists in a snow-covered environment, especially on open areas devoid of features.

Variations

A whiteout should not be confused with flat-light. Whilst there are similarities, both the causes and effects are different.

A whiteout is a reduction and scattering of sunlight. [4] [ better source needed ]

Cause: Sunlight is blocked, reduced and scattered by ice crystals in falling snow, wind-blown spin-drift, water droplets in low-lying clouds or localised fog, etc. The remaining scattered light is merged and blended.
Result: Due to a reduction in reflected light, visual references e.g. the horizon, terrain features, slope aspect, etc. are significantly reduced or completely blocked. This leads to an inability to position yourself relative to the surroundings. In severe conditions an individual may experience a loss of kinesthesia (ability to discern position and movement), confusion, loss of balance, and an overall reduction in the ability to operate.
Flat-light on Ekstrom Shelf Ice, Antarctica White-out hg.jpg
Flat-light on Ekström Shelf Ice, Antarctica

Flat-light is a diffusion of sunlight. [4] [ better source needed ]

Cause: Sunlight is both scattered and diffused by atmospheric particles (e.g. water molecules, ice crystals) and by snow lying on the ground; this causes light to be received from multiple directions. Commonly, the effect is increased during a whiteout and/or later in the day when the sun drops towards the horizon, due to sunlight passing through the atmosphere for a greater distance.
Result: Light is received from multiple directions with each light source producing overlapping shadows which cancel-out each other. This dulls the area and removes indicators such as tones and contrast, making it difficult to discern similarly coloured slope features. The loss of visual indicators of shape and edge detail results in objects and features seeming to blend into each other, producing a flat featureless vista. An effect of visual blending may be a loss of depth of field resulting in disorientation.

Hazards

Helicopter causing a whiteout with its rotor down-wash Royal Navy Commando Helicopter Force (846NAS) Merlin Mk.3 at RNoAF Bardufoss, Norway (45158529).jpg
Helicopter causing a whiteout with its rotor down-wash

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 collisions associated with whiteout conditions. One forward motorist may come to a complete stop when they cannot see the road, while the motorist behind is still moving.

Local, short-duration whiteout conditions can be created artificially in the vicinity of airports and helipads due to aircraft operations. Snow on the ground can be stirred up by helicopter rotor down-wash or airplane jet blast, presenting hazards to both aircraft and bystanders on the ground.

See also

Related Research Articles

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<span class="mw-page-title-main">Snow</span> Precipitation in the form of ice crystal flakes

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<span class="mw-page-title-main">Fog</span> Atmospheric phenomenon

Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influenced by nearby bodies of water, topography, and wind conditions. In turn, fog affects many human activities, such as shipping, travel, and warfare.

Diamond dust is a ground-level cloud composed of tiny ice crystals. This meteorological phenomenon is also referred to simply as ice crystals and is reported in the METAR code as IC. Diamond dust generally forms under otherwise clear or nearly clear skies, so it is sometimes referred to as clear-sky precipitation. Diamond dust is most commonly observed in Antarctica and the Arctic, but can occur anywhere with a temperature well below freezing. In the polar regions of Earth, diamond dust may persist for several days without interruption.

<span class="mw-page-title-main">Stratus cloud</span> Type of cloud

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<span class="mw-page-title-main">Winter storm</span> Low-temperature extreme weather events of high winds and freezing precipitation forms

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<span class="mw-page-title-main">Haze</span> Dry particulates obscuring clarity of the sky

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<span class="mw-page-title-main">Snow squall</span> Sudden heavy snowfall accompanied with strong winds

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<span class="mw-page-title-main">Ground blizzard</span>

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Blowing snow is snow lifted from the surface by the wind, at eye level or more, that will reduce visibility. Blowing snow can come from falling snow or snow that already accumulated on the ground but is picked up and blown about by strong winds. It is one of the classic requirements for a blizzard. Its METAR code is BLSN. If the snow remains below 1.8 m (6 ft), it will be called drifting snow. The snow which is being blown about may deposit as snowdrifts.

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A blizzard watch was a bulletin issued by the National Weather Service of the United States which meant winds greater than 35 miles per hour, mixed with falling or blowing snow, and visibilities of 14 mile (0.4 km) or less is forecast for a period of 3 hours or more. A blizzard watch was issued 12 to 48 hours before an expected blizzard event. As the forecast solidifies, a blizzard watch would be either downgraded to a winter storm warning or winter weather advisory for blowing snow or upgraded to a blizzard warning.

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References

  1. 1 2 3 Douglas Haig McIntosh, ed. (1972) [1916]. Meteorological Glossary. London: Her Majesty's Stationery Office. ISBN   0-11-400208-8.
  2. "Meteorology Glossary - Whiteout". American Society of Meteorology.
  3. Sir Vivian Fuchs; Sir Edmund Hillary (1958). "Glossary". The Crossing of Antarctica. London: Cassell. p. 296.
  4. 1 2 "Ask us a question". Brentaski.com. Archived from the original on July 21, 2015.