Definition
A Runway Visual Range (RVR) reading taken from a transmissometer or visibility sensor positioned at the midpoint of the runway. It reports the horizontal distance, in feet, that a pilot can expect to see down the runway from a point near its middle.
Plain English
How far you can see along the runway, measured from a sensor placed halfway down it.
Context Anchor
Seen in weather reports, tower reports, and approach information when runway visibility is low enough that runway visual range is being reported.
Derivation
RVR stands for Runway Visual Range. 'Mid' simply marks where on the runway the reading is taken — the middle — as opposed to the touchdown end (TDZ RVR) or rollout end (ROLLOUT RVR).
Why Pilots Care
MID RVR helps pilots determine whether the runway meets published landing minimums when the touchdown or rollout values are marginal.
Intuition Check
MID RVR does not mean general airport visibility. It means the visibility reading from the middle portion of a specific runway.
Example Sentence 1
Tower reported touchdown RVR 2400, mid RVR 1800, and rollout RVR 2000 for Runway 27L.
Example Sentence 2
Even though the rollout RVR was below minimums, the higher MID RVR allowed the approach to continue.