What is typically indicated by a decrease in visibility?

A decrease in visibility is typically associated with the presence of fog or precipitation. When visibility is reduced, it indicates that there is something in the atmosphere that obscures the clarity of the scene, such as water droplets in fog or rain, which scatter light and make it difficult to see clearly over distances. These weather phenomena can significantly impair visibility, posing risks for navigation and travel, especially in aviation and driving.

In contrast, improved weather conditions would generally lead to better visibility, while normal atmospheric conditions usually imply no obstructions to visibility. Stable high-pressure systems tend to be associated with clear, calm weather, which also contributes to improved visibility. Therefore, the presence of fog or precipitation is the most accurate condition described by a decrease in visibility.