When is mechanical turbulence likely to be most severe?

Mechanical turbulence is most severe in high winds due to the interaction of strong airflow with various surface obstructions such as buildings, trees, and terrain changes. When wind speeds increase, the airflow becomes disrupted as it passes over these obstacles, creating turbulent eddies and vortices in the air.

In calm weather or low wind conditions, the airflow is generally smoother, resulting in less turbulence. Clear air can also be misleading, as turbulence often increases with wind presence and surface obstructions rather than absence of visible weather phenomena. Therefore, the presence of high winds significantly magnifies the effects of mechanical turbulence, making it the correct choice in this context.