Final answer:
Surface prevailing visibility should be re-evaluated with any significant changes in weather conditions like clouds, wind, and rain, due to their impact on visibility. Constant monitoring is vital for safety in various transportation modes.
Step-by-step explanation:
The surface prevailing visibility should be re-evaluated whenever there are significant changes in the weather conditions, such as shifts in clouds, changes in wind speed and direction, or the onset of precipitation like rain. These meteorological variables can drastically alter visibility.
Given that the best observation sites can experience clear weather up to 75% of the time, constant monitoring and re-assessment are essential to maintain accurate visibility data for aviation, maritime navigation, and road traffic safety.