Visibility of less than 3 miles can indicate what potential weather condition?

Visibility of less than 3 miles often suggests the presence of fog, which is characterized by suspended water droplets in the air that can severely reduce visibility. Fog can occur when temperature and dew point are close together, leading to condensation of moisture in the atmosphere. This phenomenon is particularly common in areas with high humidity or near bodies of water.

While other weather conditions such as rain can also reduce visibility, they typically do not create the same "thickness" of reduced visibility that fog does. Furthermore, clear skies would not result in reduced visibility, and calm winds alone do not directly relate to visibility conditions. Therefore, recognizing that visibility under 3 miles typically indicates fog helps in understanding weather patterns and making informed decisions in aviation contexts.