How is visibility defined in aviation weather?

In aviation weather, visibility is defined as the distance one can see horizontally. This definition is crucial because pilots rely on horizontal visibility to determine whether it is safe to take off, land, or navigate. Horizontal visibility directly affects the pilot's ability to see and avoid obstacles, as well as to follow air traffic regulations and guidelines.

Visibility measurements are typically taken using specific instruments that assess how far a person can see in a straight line across the ground. This is particularly important in aviation, where horizontal visibility can be significantly impacted by weather conditions, including fog, rain, snow, and haze. While vertical visibility refers to how far one can see upward (often relevant in specific contexts like ceiling measurements), it does not guide a pilot's ability to navigate horizontally when flying. Thus, the focus on horizontal distance in aviation visibility helps ensure safe operations in various weather scenarios.