When the prevailing or sector visibility is less than 3 statute miles, how much must the sector visibility differ from the prevailing visibility for it to be encoded?

When the prevailing or sector visibility is less than 3 statute miles, the encoding of the sector visibility requires that it differ from the prevailing visibility by one or more reportable values. This means that even a small change in visibility is significant enough to warrant an update in the weather report.

The reasoning behind this requirement is tied to the importance of accurate weather reporting for aviation safety. When visibility is diminished, it can greatly affect a pilot’s capacity to navigate and land safely. Therefore, even a minor difference that may indicate a localized weather phenomenon (like fog or precipitation in a specific area) can provide essential information that helps in flight operations and planning. This approach ensures that the data captured reflects the conditions accurately and informs those relying on it about current visibility conditions effectively.

The other options do not align with the encoding rules in scenarios of reduced visibility, as they either specify values that are not applicable or suggest different reporting criteria that do not meet the necessary standards for effective aviation weather reporting.