What defines prevailing visibility?

Prevailing visibility is defined as the greatest horizontal visibility that is observed for at least half of the horizon circle. This means that, when assessing prevailing visibility, meteorologists look for the distance at which objects can be seen clearly in various directions, considering the maximum visibility reported over the horizon. The "at least half of the horizon circle" part is crucial, as it indicates that visibility must be sufficient in a significant portion of the environment to be classified as prevailing.

Other options, while they touch on aspects of visibility, do not capture the complete and precise definition used in meteorological practices. For instance, merely measuring horizontal visibility in kilometers or focusing solely on ground-level visibility does not provide a comprehensive understanding of prevailing visibility. Overall visibility during adverse weather conditions, while important for specific assessments, does not fulfill the requirement for continuity across a majority of the visible horizon. Thus, the emphasis on the greatest visibility over a large portion of the horizon circle is what makes this definition succinct and accurate.