Low visibility, say <1km (3300 ft), can be caused by fog when there is no/little wind present. On the other hand, high winds associated with blizzards or wildfires can also create low visibility environments. Living in a temperate climate I'd be inclined to believe that a lack of wind is the most likely cause because fog seems to be more common, however I'm not sure if this would be the case when other latitudes are also taken into consideration.

  • $\begingroup$ Have you considered dust that is raised by low velocity winds in dry regions & still lingers in the air long after the wind has subsided? $\endgroup$
    – Fred
    Jan 22 '18 at 7:39
  • 1
    $\begingroup$ @Fred: No I haven't considered that possibility. The dust storms that I have seen were associated with a descent amount of wind but you raise a good point. I could see how terrains with small particle size would not require much wind. On a smaller scale, I've seen similar situations happen with the sediment deposited after flooding. $\endgroup$
    – user11318
    Jan 22 '18 at 10:52
  • $\begingroup$ One can also have fog and wind, e.g. along mountain ridges, as moist air is elevated below the dew point. $\endgroup$
    – jamesqf
    Jan 22 '18 at 20:22
  • $\begingroup$ @jamesqf: That's another good example to consider. $\endgroup$
    – user11318
    Jan 22 '18 at 23:06

Light or calm winds do not cause reductions in visibility, but stronger winds will generally be associated with better visibilities. Poor visibility is more likely in a humid, polluted air-mass than a clean dry air-mass.

Reductions in ‘visibility’ or visual range are caused by the scattering and absorption of radiation by atmospheric particulates or aerosols. This attenuation of radiation will depend on the type, size and concentration of these particulates or aerosols. In a humid airmass water droplets can form on certain types of aerosols and these droplets can increase in size as humidity increases.

Strong winds will tend to mix the polluted air near the surface with cleaner air aloft. This mixing will also create a more uniform profile of temperature and humidity in the lowest portion of the atmosphere. If there are light winds overnight, the air near the surface becomes cooler and more humid than the air aloft. The pollutants become concentrated in this cool stable layer of air near the surface.

There are exceptions, namely advection or coastal fog. In far north-east of the U.K it’s not that uncommon to see fog with 20-30 mph winds during late spring and early summer.



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