Which of the following is NOT a typical trigger for issuing a SIGMET?

In aviation, SIGMETs (Significant Meteorological Information) are issued to alert pilots about severe weather conditions that are likely to impact flight safety. Typical triggers for issuing a SIGMET include weather phenomena that can create hazardous flying conditions, such as volcanic eruptions, severe thunderstorms, and turbulence that exceeds safe thresholds.

Localized fog conditions, while they can indeed reduce visibility, are generally not considered severe enough to warrant a SIGMET. Instead, other types of advisories or notices might be more appropriate for such conditions, as fog typically does not create the same level of widespread, significant hazard that leads to a SIGMET being issued. Thus, among the choices provided, localized fog conditions do not meet the criteria for triggering a SIGMET, making this option the correct answer.