What information does the term "Prevailing visibility" provide?

The term "prevailing visibility" refers to the greatest horizontal distance that can be seen throughout at least half of the horizon. This measurement is crucial for air traffic control and flight operations, as it gives an indication of how far a pilot or observer can see in the most visually significant areas, which typically involve a wide observation arc.

This distance can be influenced by various factors such as weather conditions (fog, rain, haze) and terrain, but it specifically measures the visibility that is most often experienced during conditions of varied visibility across the horizon. Understanding prevailing visibility helps in determining whether conditions are suitable for takeoffs and landings, particularly in low visibility situations that might impact flight safety.

The other options do not accurately describe what prevailing visibility represents. It is not limited to nighttime visibility, nor is it based on an average over 24 hours, nor does it pertain to visibility at altitude. Each of these misconceptions does not align with the standardized meteorological interpretation of prevailing visibility, which focuses on the immediate, horizontal sight distance around a location.