What is one of the requirements for the issuance of a Special Weather Report (SIGMET)?

A Special Weather Report, or SIGMET, is issued for significant meteorological events that may affect the safety of aircraft. One of the key requirements for a SIGMET is the assessment of visibility. Visibility directly impacts flight operations, especially during takeoff and landing phases, making it a crucial factor for pilots to consider.

SIGMETs are typically issued for phenomena such as thunderstorms, turbulence, or volcanic ash clouds, where specific visibility criteria may be met or severely impacted. This ensures that pilots receive timely information regarding conditions that pose a hazard during their flight routes.

While wind direction, humidity level, and cloud height can all play a role in weather assessments, they are not primary triggers for the issuance of SIGMETs. Instead, visibility is a critical aspect because it can vary rapidly and has a direct impact on aviation safety.