Variable Description

The purpose of the visibility observation is to identify reduced visibility events. For readings that come in at 3000 meters, it is implied that the visibility is 3000 meters or greater.

An observational value for visibility is based upon a "homogeneous" air mass and not specific to any given direction. For example, if a cloud bank pops in front of the sensor on an otherwise clear-as-can-be day, the visibility might be reported as 3000m because the local air mass in general is still clear, but the visibility in the direction of said cloud bank might not be 3000 meters.

Remember, visibility is not reported in a directional sense here!