If the average of all variable visibility values is less than what amount, the lowest and highest visibility values will be reported in column 14?

The correct answer is that the average of all variable visibility values must be less than 3 statute miles for the lowest and highest visibility values to be reported in column 14. This guideline is in place to ensure that significant variations in visibility, particularly in conditions where visibility is critically low, are adequately documented.

When the average visibility is under this threshold, it implies that the conditions are likely to be challenging for aviation operations, necessitating clear reporting of the extremes in visibility. This provides crucial information to pilots and air traffic controllers about the variability they might encounter, which is vital for safety and operational efficiency during flights.

If the average visibility were to exceed 3 statute miles, it is likely interpreted that visibility conditions are generally acceptable, and thus, detailed reporting of the lowest and highest variable values may not be as critical. Reporting procedures are designed to give priority to potentially hazardous conditions, especially when they fall below established thresholds that may impact flight safety.