A SIGMET is issued when certain conditions are expected to affect an area of what minimum size?

A SIGMET, which stands for Significant Meteorological Information, is issued to provide warnings about hazardous weather conditions that may affect the safety of flight operations. The issuance of a SIGMET generally pertains to weather phenomena that can impact a large area, specifically a minimum of 3000 square miles. This area size is significant enough to ensure that the potential impact of severe weather is communicated effectively to pilots and airlines.

The conditions under which a SIGMET is issued include various weather phenomena such as thunderstorms, turbulence, severe icing, and volcanic ash, among others, which can necessitate widespread awareness for those operating in or near the affected area. The requirement for this minimum area size emphasizes the importance of informing the aviation community about hazards that are not localized but rather have the potential to affect multiple aircraft and flight paths.