Regarding SIGMETs, which statement is true for the contiguous U.S.?

The correct statement regarding SIGMETs for the contiguous U.S. is that they are issued as a convective SIGMET when obscured thunderstorms are forecast. Convective SIGMETs are specifically designed to alert pilots of significant convective weather events, such as thunderstorms that may not be easily identifiable on standard radar due to cloud cover or other obstructions. This includes conditions like severe turbulence, hail, and lowered visibility caused by heavy precipitation, making it crucial for flight safety.

The other options do not accurately reflect how SIGMETs function within the aviation weather reporting system. SIGMETs are not issued for all types of severe weather, as they specifically focus on phenomena that could impact the safety of flight, such as turbulence, thunderstorms, or volcanic ash. While turbulence may be a factor in SIGMET issuance, it is not exclusively categorized under a separate SIGMET type. Additionally, SIGMETs are not limited to winter months; they are issued year-round in response to relevant weather conditions.