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Caren Marzban
,
Stephen Leyton
, and
Brad Colman

1. Introduction Coastal locations around the United States are susceptible to marine stratus and low ceilings. Occasionally, the stratus extends to the surface, resulting in dense fog conditions and a significant reduction in horizontal visibility. When these adverse conditions occur, they often disrupt daily activities, such as aviation and shipping interests, sometimes to the point of jeopardizing human safety. It is imperative, then, to provide forecasters with the most accurate guidance for

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Rong Tang
,
Qian Li
, and
Shaoen Tang

1. Introduction Atmospheric visibility ( Horvath 1981 ) is defined as the maximum horizontal distance that a person with normal vision can see objects from the sky background under certain weather conditions. It is an important element of ground meteorological observations ( Hautiere et al. 2010 ) and plays an important role in ensuring the safety of aviation, road traffic, and military operations. Therefore, detecting visibility accurately and getting the early warning of low visibility

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Bu-Yo Kim
,
Miloslav Belorid
, and
Joo Wan Cha

1. Introduction The World Meteorological Organization (WMO) defines visibility as the distance at which light intensity is reduced to 5% of the original intensity ( WMO 2014 ). In unpolluted atmospheric conditions, visibility lies in the range from several tens to hundreds of kilometers; however, low visibility of several kilometers can be caused by suspended particle matter and gases in the atmosphere ( Wu et al. 2012 ). High energy consumption due to urbanization and industrialization

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Qiang Huang
,
John Hanesiak
,
Sergiy Savelyev
,
Tim Papakyriakou
, and
Peter A. Taylor

1. Introduction Blowing snow is a common weather phenomenon in the Canadian Arctic and prairies. It occurs when the wind is strong enough to raise the snow particles to sufficient heights above ground that horizontal visibility (meteorological optical range, MOR; also described as Vis thereafter) is reduced to 9.7 km (6 mi) or less ( Atmospheric Environment Service 1977 ). It can be a hazard to public safety and transportation since the visibility can be significantly reduced in some blowing

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Richard M. Chmielecki
and
Adrian E. Raftery

1. Introduction The accurate prediction of visibility even over short-term (0–6 h) forecasting periods is challenging. Since most numerical weather prediction models do not explicitly model visibility, forecasts of visibility must first be derived from other meteorological parameters such as cloud water content, relative humidity, and precipitation. There are a handful of different specifications of visibility as a function of other weather parameters ( Knapp 1999 ; Doran et al. 1999

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Bjarne Hansen

airports. The Meteorological Service of Canada (MSC) is responsible for providing accurate and timely weather forecasts for 190 airports across Canada. The forecasts describe weather conditions expected to affect flight conditions for up to the next 24 h. These conditions include cloud ceiling height, horizontal visibility, precipitation, and wind direction and speed. Forecasters work to keep these forecasts as accurate and current as possible, and will quickly revise forecasts as appropriate for the

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I. Gultepe
and
J. A. Milbrandt

1. Introduction Visibility (Vis) parameterizations as a function of relative humidity with respect to water (RH w ) and precipitation rates (PR) are important for many weather forecast–related applications, including aviation, transportation, and search and rescue operations ( Gultepe et al. 2007 ; Tardif 2007 ). In past applications, Vis parameterizations have been used in various models that include numerical weather prediction (NWP) models ( Stoelinga and Warner 1999 ) and fog models

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Zhongping Lee
and
Shaoling Shang

observed and whether an object is visible or not impacts decision-making and management. Subsequently, the term “visibility” has been used to provide a quantitative representation of this information throughout the past decades. However, there is no unified definition of visibility, although it is usually referred to as the distance of “an object will be just visible ” ( Duntley 1948b , p. 237; Malm et al. 1980 ; Middleton 1947 ), as adopted by the International Civil Aviation Authority (ICAA). On

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Sonu Mathew
and
Srinivas S. Pulugurtha

1. Introduction Rainfall and poor visibility disrupt the operational performance of roads in different ways. The reduction in travel demand and road capacity ( Agarwal et al. 2005 ; Maze et al. 2006 ; Datla and Sharma 2008 ), deterioration in safety performance, and the worsening of travel speed or travel time ( Agarwal et al. 2005 ; Koetse and Rietveld 2007 ) are the significant effects of such weather conditions on the operational performance of roads. Per the National Highway

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Gary L. Achtemeier

1. Introduction Dense fog reducing visibility to a few meters has been implicated as a causal factor of multiple-vehicle accidents in all sections of the United States and parts of Canada ( Pagowski et al. 2004 ). An additional factor contributing to the frequency of extreme fog events is the combination of fog with smoke from prescribed burns ( Achtemeier et al. 1998 ). Land managers in the southern United States (states from Virginia to Texas and from the Ohio River southward) use prescribed

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