When is vertical visibility reported in Terminal Aerodrome Forecasts (TAF)?

Vertical visibility is reported in Terminal Aerodrome Forecasts (TAF) specifically when there are conditions that obscure the view of the sky. This typically occurs during situations like dense fog, heavy precipitation, or other atmospheric conditions that prevent the observer from seeing through the lower layers of the atmosphere.

When the sky is overcast or clear, the visibility is generally not reported since the conditions are stable enough to see the cloud cover or the sky above without obstruction. Similarly, fog does lead to obscured visibility, but vertical visibility becomes particularly relevant when it cannot be measured in the usual way because of these obscure conditions. Reporting vertical visibility gives pilots critical information about their immediate flying environment, allowing them to make more informed decisions regarding takeoffs and landings in conditions where normal visibility is compromised.