Which advisory signifies the likelihood of severe thunderstorm development?

The correct answer is Convective SIGMET. This advisory specifically highlights the occurrence or potential development of severe thunderstorms. Convective SIGMETs are issued by the National Weather Service and indicate significant weather phenomena such as severe turbulence, severe thunderstorms, and tornadoes, among other conditions that originate from convective activity.

The issuance of a Convective SIGMET signifies that forecasters have assessed conditions in a specific area that meet the criteria for severe weather, thus alerting pilots and dispatchers about potentially hazardous flying conditions. This information is crucial for flight planning and safety.

In contrast, while Flash Flood Advisories and Wind Shear Advisories address other forms of severe weather, they do not specifically focus on the development of severe thunderstorms. Severe Weather Alerts may sound broad enough to suggest a range of severe weather conditions, but they do not convey the same specificity regarding thunderstorms as a Convective SIGMET does.