Definition
The distance an observer can see straight up into an obscuring layer such as fog, heavy precipitation, or smoke, reported when the sky is fully obscured and a normal cloud ceiling cannot be determined. In a METAR it appears as VV followed by a three-digit height in hundreds of feet above the ground (for example, VV004 means vertical visibility of 400 feet).
Plain English
When the sky is hidden by something like fog or heavy snow, vertical visibility is how far you can see looking straight up before the view disappears into the murk.
Context Anchor
Seen in airport weather reports when the sky is obscured by fog, snow, smoke, or similar conditions.
Derivation
Vertical comes from a Latin word meaning the highest point or directly overhead. Visibility comes from words meaning able to be seen. Together, the term points to what can be seen directly upward, not outward along the horizon.
Why Pilots Care
Tells a pilot the effective ceiling height for takeoff and landing decisions when the sky cannot be seen.
Grounding Statement
Picture standing on the ramp in thick fog and looking straight up; vertical visibility is how high into that fog you can see before everything disappears.
Intuition Check
Do not read vertical visibility as normal forward visibility turned sideways. It specifically means how far upward you can see into an obscuring layer when the sky itself is hidden.
Example Sentence 1
The METAR reported VV002, meaning vertical visibility was only 200 feet in dense fog.
Example Sentence 2
Because vertical visibility remained below 500 feet, the pilot waited for conditions to improve before departing VFR.