What is the meaning of the METAR abbreviation 'FZFG'?

The METAR abbreviation 'FZFG' stands for "Freezing Fog." This term is used in aviation meteorology to describe a specific type of fog that occurs when water droplets are supercooled and remain in liquid form even though the temperature is at or below freezing. This phenomenon can lead to hazardous conditions, as it can create icy surfaces on roads, runways, and other structures, significantly impacting visibility and safety.

In METAR reports, aviation weather observers use this abbreviation to indicate that freezing fog is present, alerting pilots and ground crews to potential risks. The presence of freezing fog can be critically important for flight operations, as it can reduce visibility to less than one mile and may also cause icing on aircraft.

Other choices like "Fog," "Unknown Precipitation," and "Thunderstorm" do not accurately represent this specific weather phenomenon. While fog generally refers to reduced visibility caused by water vapor and is not specific about temperature, 'FZFG' emphasizes the freezing aspect, making it distinct from ordinary fog. The other options do not convey the specific implications related to freezing conditions and their effects on aviation safety.