What meteorological condition is most likely to produce turbulence in flight?

Cumulonimbus clouds are particularly significant in relation to turbulence because they are associated with strong upward and downward air currents, particularly during thunderstorms. These clouds can develop massive vertical structures, leading to significant atmospheric instability and producing severe turbulence as air rapidly ascends and descends. Pilots should be cautious around cumulonimbus clouds due to the potential for severe turbulence, lightning, and other hazardous weather phenomena.

While high-pressure systems can provide stable weather conditions generally leading to less turbulence, and warm, moist air masses might contribute to instability, these conditions do not create turbulence as intensely or directly as cumulonimbus clouds. Clear air turbulence can also occur in various flight conditions but is typically associated with the presence of jet streams and clear skies rather than specific cloud formations. Therefore, cumulonimbus clouds are a primary indicator of turbulence during flight due to their strong convective activity.