Visibility
Understand why visibility falls because of fog, dust, smoke, rain or moisture and how to interpret a visibility reading.
What visibility means
Visibility estimates how far an observer can distinguish objects under current atmospheric conditions. Water droplets, particles, precipitation and lighting can all affect it.
Fog and mist
When air near the surface becomes saturated, water can condense into tiny droplets. These droplets scatter light and reduce the distance at which objects can be distinguished. Fog can form overnight, near water or when moist air moves across a cooler surface.
Dust and smoke
Dry regions can experience reduced visibility when wind lifts dust or sand. Smoke and fine particles can also create haze even when there are few clouds. These causes are different from rainfall but can occur at the same time.
Rain and visibility
Heavy rain can temporarily reduce visibility because water droplets scatter light. Drivers should consider visibility together with road conditions, wind and precipitation intensity.
Use the number carefully
Visibility can change quickly and can vary between nearby locations. For travel, combine the reading with local observations, forecasts and official warnings.
Worked example: converting a visibility forecast
Suppose a forecast gives 800 metres at 06:00 and 8,000 metres at 10:00. Divide by 1,000 to compare 0.8 km with 8 km. These hypothetical numbers suggest a substantial improvement during the morning; they do not establish the exact time every road will clear.
A low river crossing can remain foggy after an exposed nearby site improves. Before a journey, compare the intended route with current transport reports and conditions you can actually see. WeatherRadarNow displays modeled visibility, not a camera or roadside visibility sensor.
Does poor visibility mean polluted air?
Not necessarily. Fog droplets can strongly reduce visibility even without a smoke or dust event. Conversely, air pollution may be significant while distant objects remain visible. A visibility number is not an air-quality index and cannot identify the substance reducing visibility.
Why can visibility look different toward the sun?
Glare, contrast and lighting affect what a person can distinguish. A weather visibility estimate does not account for every direction of view, dirty windscreen or unlit object. Do not translate the number into a safe driving speed.
Travel guidance
For reduced-visibility travel, consult NWS fog safety guidance and the transport authority responsible for your route. See also humidity and condensation and using weather information safely.
Editorial note: Weather information varies by location, observation source and update time. This article is for general education and everyday planning. For severe weather or safety-critical decisions, follow the relevant official meteorological and emergency authorities.