If visibility is reduced to less than 5/8 statute mile due to low cloud, what is this phenomenon called?

When visibility is reduced to less than 5/8 statute mile primarily due to low cloud cover, the phenomenon is referred to as fog. Fog is characterized by a dense cloud of water droplets suspended in the air near the ground, which significantly impairs visibility. It typically occurs when the temperature and dew point are very close, leading to condensation of water vapor and the formation of clouds at or near ground level.

In meteorological terms, fog is defined by its visibility criteria, and its formation is often associated with specific atmospheric conditions such as high humidity and low temperatures, making it distinct from other visibility-reducing phenomena. While haze can also reduce visibility, it is generally caused by particulate matter in the air and does not meet the same criteria as fog in terms of cloud formation. Low visibility is a broader term and does not specify the presence of clouds. Stratus clouds are a type of low cloud that can lead to fog when they are thick enough to bring visibility below 5/8 statute mile, but the direct phenomenon is fog itself. Thus, the correct identification of fog clarifies the specific condition affecting visibility in this scenario.