What contraction is used to indicate a completely obscured sky condition?

The contraction used to indicate a completely obscured sky condition is "VV," which stands for "vertical visibility." This term is particularly relevant in situations where the sky is so overcast or obscured by fog, haze, or other phenomena that the horizon cannot be defined from the ground, making it impossible to see any portion of the sky. Vertical visibility indicates how far upward one can see vertically through the obscuring layer, which is critical for pilots and meteorologists who require a clear understanding of cloud cover and conditions that might affect flying.

In contrast, the other contractions represent different levels of cloud cover. "OVC" stands for overcast, which indicates that the sky is completely covered by clouds, but it does not imply any obstruction of visibility from a vertical perspective. "BKN" indicates broken clouds, meaning there are significant gaps in the cloud cover, while "SCT" signifies scattered clouds, implying that clouds are present but are not dominating the sky. Therefore, "VV" is the most appropriate answer for describing a situation where the sky is completely obscured to the point of requiring vertical visibility measurement.