What is a SIGMET issued for?

A SIGMET, or Significant Meteorological Information, is specifically issued to highlight severe weather conditions that can impact flight safety, primarily those that are not related to convective activity, such as thunderstorms. In this context, the issuance of a SIGMET for severe icing not associated with thunderstorms is pertinent because it informs pilots of hazardous conditions that could lead to loss of control or significant changes in aircraft performance.

Severe icing can form under certain atmospheric conditions and poses serious risks to aircraft, especially during takeoff and landing or in regions where the weather is not easily identifiable through standard weather reports. Therefore, it is crucial for pilots to be aware of such conditions, making the SIGMET an essential tool for aviation safety.

The other conditions listed, while they may represent challenging weather scenarios, do not meet the criteria for SIGMET issuance. For example, light turbulence in clear air, extreme fog, or minor weather disturbances do not generally rise to the level of severity that necessitates a SIGMET, as they may not pose immediate or serious hazards to flight operations.