What conditions are most favorable for wave formation over mountainous areas?

The conditions described in the correct answer highlight the importance of a stable layer of air at mountaintop altitude, combined with a sufficient wind speed. When there is a stable layer of air present, it acts as a lid that traps the airflow below it. When wind blows over mountains or ridges, this creates an upward motion due to the wind being deflected upwards by the terrain. If the wind speed is at least 20 knots, it generates enough lift and turbulence to form waves, which can develop into significant wave patterns.

The combination of stable air and adequate wind speed allows for the development of mountain waves, which are characterized by a series of oscillations or waves downwind of the mountains. These conditions lead to predictable wave formations that are important for pilots operating lighter-than-air craft, providing them with insights into potential lift or turbulence in the area.

In contrast, unstable air, low wind speeds, or other environmental conditions do not support the same type of wave formation. Unstable air would disrupt the smooth airflow necessary for waves, while low winds do not provide sufficient energy to create the pronounced wave patterns that would be beneficial for navigation and performance in lighter-than-air aviation.