Report sector visibility in the remarks whenever it:

The requirement to report sector visibility in the remarks comes into play specifically when it differs from the prevailing visibility by one or more reportable values and is less than 3 miles. This condition emphasizes the need for pilots and other users of weather information to be aware of significant variances that may impact visibility for flight operations.

When the sector visibility is reported under these circumstances, it serves as a critical update that allows for an accurate assessment of current conditions. For example, if prevailing visibility is 5 miles, but sector visibility is 2 miles, this discrepancy could indicate localized adverse conditions that might hinder safe navigation or approach procedures.

In aviation, maintaining awareness of visibility conditions is essential for safety. Therefore, the reporting of such variations, especially when they fall below a specific threshold, ensures that all operational decisions are informed by the most accurate and relevant information available.