Private Pilot Private Exam

Possible mountain wave turbulence could be anticipated when winds of 40 knots or greater blow...

1. Along the coast

2. Across a mountain ridge in stable air

3. Over flat terrain

4. At lower altitudes

The correct answer is: Across a mountain ridge in stable air

Mountain wave turbulence is most likely to occur when strong winds, specifically 40 knots or greater, blow across a mountain ridge in stable air. This phenomenon is caused by the lifting and subsequent descent of air as it interacts with the terrain. When winds encounter a mountain, they are forced upward, creating an upward motion on the windward side of the ridge. If these winds are strong enough and the atmosphere is stable—meaning there is little vertical movement of air—this can lead to the development of waves that propagate downwind. As these waves move down the leeward side of the ridge, they can generate significant turbulence due to the oscillating nature of airflows. In contrast, the other options do not create the same conditions for mountain wave turbulence. For instance, winds along the coast may encounter different effects due to proximity to the sea and variability in surface temperatures. Over flat terrain, there are generally no significant obstructions to cause the necessary lifting and wave formation. Finally, lower altitudes alone do not contribute to the conditions that foster mountain wave turbulence without the influence of terrain or stable atmospheric conditions.