Which abbreviation indicates that visibility is reduced due to fog?

The abbreviation that indicates that visibility is reduced due to fog is "FG." This code is used in aviation meteorology and is part of the METAR reports, which are the standard format for reporting weather information at airports.

Fog is defined as a weather condition where water droplets are suspended in the air, leading to significantly reduced visibility, generally defined as less than 5/8 statute miles. The presence of fog can greatly impact flight operations, making it essential for pilots to be aware of such conditions.

In contrast, the other abbreviations represent different weather phenomena. "BR" stands for mist, which causes a reduction in visibility but not as severe as fog. "FZFG" refers to freezing fog, which is fog that can cause surface conditions to become icy due to freezing water droplets, and thus indicates a more specific type of fog. Lastly, "HZ" stands for haze, which reduces visibility to a lesser degree than fog and is typically a result of particles or pollutants in the air rather than moisture condensing on droplets.

Understanding these distinctions is crucial for interpreting weather reports and ensuring safe flight operations.