Which weather condition is indicated by the abbreviation "FC" as a significant weather event?

The abbreviation "FC" stands for "funnel cloud," which is a significant weather event indicating a rotating column of air extending from a thunderstorm base to the ground. Funnel clouds are often precursors to tornadoes and are associated with severe weather conditions, making them vital for UAV operators to understand when assessing flight safety. Recognizing and responding to this type of weather condition is crucial for the safety of drone operations.

In contrast, the other options do not represent significant weather events in the same way. Storms may encompass a variety of weather phenomena, and while they can be hazardous, the abbreviation "FC" specifically indicates funnel cloud activity. Cloud formation is a general term that does not specify severe weather conditions, and cirrus clouds refer to a high-altitude cloud type that typically does not signify impending severe weather. This specificity makes "FC" significant in the context of weather-related dangers for unmanned aircraft operations.