What information is contained in a special CONVECTIVE SIGMET in the conterminous United States?

A special CONVECTIVE SIGMET is specifically designed to provide crucial information about significant convective weather phenomena that can impact flight safety. The correct choice highlights that it includes warnings about tornadoes, embedded thunderstorms, and hail that is 3/4 inch or greater in diameter.

The emphasis on tornadoes and embedded thunderstorms is important because these conditions typically indicate severe and rapidly changing weather that can be hazardous for aviation. Hail of significant size not only poses a danger to aircraft but can also be indicative of a severe thunderstorm environment.

While the other options mention important weather phenomena, they refer to different types of weather alerts. For example, moderate thunderstorms and surface winds greater than 40 knots are mentioned in a general SIGMET rather than in a special CONVECTIVE SIGMET. Similarly, severe icing, severe turbulence, or widespread dust storms are also outside the scope of what is covered in a special CONVECTIVE SIGMET, as they pertain to non-convective weather conditions. Thus, the correct answer reflects the specific severe weather threats that warrant heightened caution and are categorized under a special CONVECTIVE SIGMET.