When visibility is reported as 10SM, what does this indicate?

When visibility is reported as 10 statute miles (SM), it indicates that visibility is exactly 10 statute miles. In aviation meteorology, visibility is an important parameter for safe aircraft operations, and a report of 10SM clearly conveys that pilots can expect visibility to be at that specific distance.

The use of "10SM" communicates that pilots should anticipate conditions where they can see up to 10 statute miles. This information is vital for various operational aspects such as takeoff and landing procedures, as well as overall flight safety. Understanding that it reflects an exact figure rather than a range helps pilots make informed decisions about their approach and navigation.

In contrast, the other choices suggest variations of visibility that do not align with the standard interpretation of a visibility report. For example, saying visibility is under or above 10 statute miles introduces uncertainty, which is not reflected in a precise report of 10SM. Similarly, mentioning nautical miles would imply a different measurement system, which is not applicable in this context since the report uses statute miles as its unit.