What is reported in column 9 when patches of fog exist but the prevailing visibility is 7 miles?

When patches of fog are present, the appropriate aviation weather reporting code to use is "BCFG." This code specifically indicates the presence of fog that occurs in patches, which can affect visibility. In this scenario, despite the prevailing visibility being 7 miles, the existence of patches of fog is significant enough to warrant a report in column 9 of the observation.

The presence of the term "BCFG" in the report serves to alert pilots and air traffic controllers to the localized areas of reduced visibility that may not affect the overall prevailing visibility, which remains relatively good at 7 miles. This is important for flight safety, as even patches of fog can create sudden and localized changes in visibility that could impact aircraft operations, particularly during takeoff and landing.

Other codes such as "BR" refer to mist, which indicates reduced visibility but does not specifically address fog patches. "VCFG" would denote visibility in those fog patches but is usually used when visibility is below certain thresholds that warrant attention. However, since the question specifically notes the prevailing visibility is 7 miles, "BCFG" is the most appropriate and correct choice in this context.