M1, S2, C5 - Prevailing Visibility

Question 1

Prevailing visibility is defined as…

Answer 1

…the visibility value that is reached or exceeded within at least half the horizon circle or within at least half of the surface of the aerodrome.

These areas could comprise contiguous or non-contiguous sectors.

Question 2

The prevailing visibility at an observing station will always be reported.

The lowest visibility observed will also be reported…

Answer 2

…Where the visibility in any direction is less than the prevailing visibility and less than 1500m or less than 50% of the prevailing visibility.

The general direction of the area of lower visibility will be indicated by reference to one of the eight points of the compass.

If the lowest visibility is observed in more than 1 direction, then the most operationally significant direction will be reported.

When the visibility is fluctuating rapidly and the prevailing visibility can not be determined, only the lowest visibility will be reported, with no indication of direction.