A convective SIGMET primarily deals with what weather phenomenon?

A convective SIGMET is specifically focused on thunderstorms and associated severe weather phenomena. These alerts are issued by the National Weather Service to inform pilots of significant convective activity that may impact flight safety. Thunderstorms can produce severe turbulence, hail, downbursts, and tornadoes, all of which can pose serious risks to aircraft in flight.

While other weather phenomena such as fog, heavy rain, and high winds can indeed affect aviation, they are not the primary focus of a convective SIGMET. Fog is typically addressed through different advisories, heavy rain can be part of other weather observations but does not specifically indicate a severe risk like thunderstorms do, and high winds may be highlighted in other types of advisories as well, but they are not categorized under convective SIGMETs unless tied directly to severe convective activity. Thus, the emphasis on thunderstorms in the definition of convective SIGMETs makes it clear why this is the correct answer.