When is vertical visibility forecast in a TAF?

Vertical visibility is forecast in a TAF when the sky is obscured due to a surface-based phenomenon. This condition typically arises in scenarios such as fog, heavy rain, or snow, where the view of the sky is obscured, limiting the vertical visibility, although horizontal visibility may still be acceptable.

Under these circumstances, it's essential to provide pilots with a forecast that indicates how high they can see upward from the surface, which is known as vertical visibility. This is crucial for safe takeoff and landing operations, particularly in airports where these phenomena could affect aircraft operations.

In contrast, if the sky is clear, if visibility exceeds ten kilometers, or during conditions with no significant weather, vertical visibility would not need to be addressed in the TAF because the visibility conditions are not restrictive. Therefore, the correct context for the inclusion of vertical visibility in a TAF is specifically when the sky is obscured due to factors mentioned, making it critical information for flight safety.