Which weather phenomenon is most likely to produce severe icing?

Thunderstorms are indeed the weather phenomenon most likely to produce severe icing. This is largely due to the vigorous updrafts and downdrafts commonly found within thunderstorms, which can carry supercooled water droplets to higher altitudes where temperatures are below freezing. When these supercooled droplets come into contact with aircraft surfaces, they can freeze rapidly, leading to significant icing. This icing can accumulate quickly and severely, creating hazardous flying conditions.

In contrast, light rain showers are typically not associated with the same intensity or structure found in thunderstorms, making them less likely to produce severe icing. Clear skies generally indicate stable atmospheric conditions, which also do not favor severe icing. Overcast conditions can sometimes lead to icing if temperatures are low enough, but they do not usually produce the severe conditions associated with thunderstorms. Thus, thunderstorms stand out as the prime scenario for severe icing due to their dynamic and turbulent nature.