What is the primary risk associated with mountain wave turbulence?

Mountain wave turbulence is primarily associated with sudden and severe altitude fluctuations. This phenomenon occurs when stable air flows over mountain ranges, causing the airflow to be disrupted and creating powerful updrafts and downdrafts. As aircraft traverse these regions, they can unexpectedly encounter significant changes in altitude, which can lead to challenges in maintaining control of the aircraft.

The turbulence is particularly dangerous because it can occur without warning, making it difficult for pilots to anticipate and respond effectively, especially in mountainous areas where visual references may be limited. Understanding this risk is crucial for flight planning and safety in mountainous regions.

The other options do not align with the nature of mountain wave turbulence; for instance, enhanced visibility, increased ground speed during approach, and stable air conditions are contrary to the disruptive nature of the turbulence experienced in such environments.