What does "VV" indicate when the sky is totally obscured?

"VV" stands for "Vertical Visibility," which is used in aviation weather reports to indicate that the sky is totally obscured. This condition occurs when the observer is unable to determine the sky's condition due to heavy precipitation, fog, or other obstructions. Vertical visibility is a measure of how far one can see vertically through the obscuration, such as when looking straight up.

In aviation, understanding vertical visibility is crucial for pilots as it informs them of potential hazards relative to clouds and other obstructions in the vertical plane. This measurement helps in assessing whether an aircraft can safely operate under certain conditions, especially during approaches and landings where visibility is paramount. Therefore, identifying "VV" as vertical visibility aids pilots in making better-informed decisions regarding flight safety during periods of total sky obscuration.