When the visibility decreases from 1 mile to 1/2 mile in fog and the temperature drops, what should be reported?

When visibility decreases from 1 mile to 1/2 mile in fog, the appropriate observation to report is classified as "FG," which indicates fog. In aviation weather reporting, fog is defined as a condition where the visibility is less than 1 statute mile and is caused by the suspension of small water droplets in the air, resulting in reduced visibility.

Since the visibility has decreased to 1/2 mile, it meets the criteria for fog, justifying the report of "FG." The presence of fog is also consistent with a drop in temperature, as colder air can hold less moisture, leading to saturation and the formation of fog. This is an important detail in meteorological observations, as temperature can be a contributing factor to the development of fog.

The other options represent different meteorological phenomena. For instance, "FZFG" indicates freezing fog, which would only be reported if the visibility was reduced due to fog and temperatures were below freezing, leading to ice formation. "BR" signifies mist, typically reported when visibility is reduced to between 5/8 and 1 statute mile, which does not apply in this case since visibility is below 1/2 mile. Finally, "FZBR" would indicate freezing mist, also