What visible signs indicate extreme turbulence in thunderstorms?

The presence of cumulonimbus clouds and roll clouds serves as strong indicators of extreme turbulence typically associated with thunderstorms. Cumulonimbus clouds are characterized by their tall, towering formations that can reach high altitudes and are often associated with severe weather phenomena, including strong winds, heavy precipitation, hail, and lightning. These clouds are a clear sign of vertical instability within the atmosphere, which contributes to turbulence.

Roll clouds, on the other hand, are formed at the base of a cumulonimbus cloud and often signify the presence of strong gust fronts or the leading edge of a cold outflow from the storm. These rolling formations can add to the atmospheric disturbances in the vicinity, further indicating turbulent conditions.

In contrast, other options fail to indicate the turbulence associated with thunderstorms. Stratus clouds typically represent stable atmospheric conditions and are not associated with severe turbulence. Heavy rain can occur without extreme turbulence, and scattered clouds alongside lightning, while indicative of potential thunderstorm activity, do not provide the same robust visual signal of turbulence as cumulonimbus and roll clouds. Lastly, light winds and clear skies suggest calm weather rather than turbulent conditions.