What conditions can trigger the issuance of a SIGMET?

SIGMETs, or Significant Meteorological Information, are issued for various weather phenomena that can impact the safety of flight operations. The correct conditions that trigger the issuance of a SIGMET include phenomena such as heavy turbulence, severe icing, and other significant weather events that could pose a hazard to aircraft.

Heavy turbulence is referenced because it can result from various factors including strong winds, unstable air, or large weather systems. Extreme icing is critical as ice accumulation on aircraft can lead to severe aerodynamic problems, making safe flight difficult. Therefore, the issuance of a SIGMET during conditions of heavy turbulence and extreme icing is essential for alerting pilots to potential dangers.

When considering the other conditions listed, low visibility and fog, high winds and rain, while they can affect flight safety, are usually addressed with different types of advisories like AIRMETs or specific terminal weather alerts, not necessarily SIGMETs. Thunderstorms alone would not trigger a SIGMET unless they present severe conditions like hail or wind shear. Therefore, the specific combination of heavy turbulence and extreme icing aligns with the purpose of a SIGMET to inform pilots of significant and potentially hazardous meteorological conditions affecting aviation.