What is the prevailing visibility when the visibility is varying between 6sm and 10sm during observation?

The prevailing visibility is determined by assessing the visibility conditions during a specific observation period. When the visibility is reported as varying between 6 statute miles (sm) and 10 sm, the prevailing visibility is taken as the most frequently occurring visibility within that range—essentially the value closest to the midpoint of the variability.

In this case, since visibility fluctuates between 6 sm and 10 sm, the average can be calculated as follows: the midpoint between 6 sm and 10 sm is 8 sm. This means that visibility often falls around this value during the observation, indicating that 8 sm is the most representative figure of the overall visibility condition during that observation period. This aligns with the definition used in aviation reporting, where the prevailing visibility indicates the most common visibility conditions experienced.

The other choices represent visibility values that do not reflect the average or the most frequently observed visibility in the stated range. Thus, they do not accurately represent the prevailing visibility in this situation.