What is indicated when a current CONVECTIVE SIGMET forecasts thunderstorms?

• A. Thunderstorms obscured by massive cloud layers
• B. Thunderstorms with no cloud cover
• C. Thunderstorms with only lightning
• D. Thunderstorms with clear air turbulence

Answer: (A)

Convective SIGMETs warn of thunderstorm activity that can pose significant hazards to flight, and that activity may be hidden inside thick cloud layers. When you see a forecast for thunderstorms, you should expect storm cells that could be embedded, in lines, or obscured by large cloud buildups such as cumulonimbus and anvils, meaning the weather may not be visually detectable from the cockpit or on simple radar. This hidden nature is a key reason why these SIGMETs are issued—to alert you that dangerous weather can be present even if the sky looks deceptively clear.

Thunderstorms with no cloud cover aren’t possible, since a thunderstorm relies on clouds. Thunderstorms with only lightning ignores the broader hazards associated with convective activity, and isn’t what a Convective SIGMET conveys. Clear air turbulence can accompany or occur near storms, but the SIGMET highlights the storms themselves and their hazards, not turbulence alone.