Which inflight advisory provides a forecast of embedded thunderstorms?

The correct answer is based on the function of SIGMETs, which are advisories that specifically address significant weather phenomena that may pose a hazard to aviation. A SIGMET provides information about severe weather, including thunderstorm activity that can be particularly dangerous due to embedded thunderstorms. These thunderstorms can be difficult to detect visually and can significantly impact flight safety, making SIGMETs crucial for pilots to understand current weather conditions.

In contrast, AIRMETs are used for less severe weather conditions and do not focus specifically on embedded thunderstorms. The SEVERE ALERT is not a standard advisory term recognized in aviation meteorology and might be considered a generalized term rather than a specific forecast type. METAR refers to routine aviation weather reports, providing information on current weather conditions but not forecasts or advisory details about severe weather phenomena like embedded thunderstorms.

Thus, knowing that SIGMETs specifically address severe conditions, including embedded thunderstorms, highlights why this option is the most relevant and accurate in the context of inflight advisories.