What causes turbulence in flight?

Turbulence in flight is primarily caused by irregular airflow, which can significantly affect the smoothness of a flight. This irregularity can arise from various sources, including weather conditions such as thunderstorms, wind shear, and atmospheric pressure changes. Turbulence is also influenced by terrain; for instance, when air flows over mountains, it can create disturbances in the airflow. Additionally, wake turbulence is generated by other aircraft, particularly larger ones, which can result in sudden and unexpected changes in air movement that affect following aircraft. This multifaceted nature of turbulence highlights how external environmental factors interplay to create disruptions in the airflow, thereby causing the bumpy ride that passengers may experience during flight.

The other options do not accurately describe the primary causes of turbulence. Constant airflow at high altitude tends to be more stable, and excessive weight or lack of maintenance relates more to aircraft performance and safety rather than directly causing turbulence in the atmosphere.