What is the maximum valid period of a SIGMET for Severe turbulence?

The maximum valid period of a SIGMET for severe turbulence is indeed four hours. SIGMETs are important weather advisories that warn pilots of significant weather phenomena that can affect the safety of flight operations. They are issued to highlight conditions like severe turbulence, icing, thunderstorms, and other hazardous weather.

The reason for the four-hour validity period for SIGMETs related to severe turbulence is tied to the nature of atmospheric conditions. Weather changes can occur rapidly, and keeping SIGMETs current helps ensure that pilots have the most accurate information available for their routes. A four-hour timeframe strikes a balance between providing timely warnings while allowing for reasonably short updates as conditions evolve.

In this context, the maximum periods for other types of SIGMETs or various other phenomena differ, reflecting their unique characteristics and how long pilots might need to be informed about them. For example, other weather advisories might extend longer than four hours due to the slower nature of changes in those conditions. Understanding these time limits is crucial for safe flight planning and operation.