FAA Airline Transport Pilot (ATM)Meteorology and Weather ServicesMedium
A pilot flying downwind of a mountain range at cruise altitude reports smooth, lens-shaped clouds visible above and downwind of the ridgeline, along with turbulence encountered in otherwise clear air near those clouds. What phenomenon is most likely causing this turbulence?
- AFrontal turbulence along an approaching cold front
- BWake turbulence from a preceding aircraft
- CMountain wave turbulence
- DConvective turbulence from surface heating
Show answer & explanationAnswer & explanation
Correct answer: C. Mountain wave turbulence
Strong winds blowing perpendicular to a mountain ridge in a stable atmosphere create a wave pattern downwind, marked by lenticular (lens-shaped) clouds at the wave crests and often severe turbulence, including rotor turbulence, near the surface.
Why the other options are wrong
- A. Frontal turbulence would be accompanied by a frontal weather system, not isolated lenticular clouds.
- B. Wake turbulence comes from another aircraft's wingtip vortices, unrelated to terrain or lenticular clouds.
- D. Convective turbulence is associated with thermals and cumulus buildups, not lenticular clouds.
Mountain Wave Turbulence
Turbulence caused by strong winds flowing perpendicular over a mountain range in stable air, creating an oscillating wave pattern downwind marked by lenticular clouds.
- Requires stable air and wind speed generally over 25 knots perpendicular to ridge
- Lenticular clouds mark wave crests; rotor clouds mark severe low-level turbulence
- Can extend turbulence well above and downwind of the mountain range
Memory trick: Mountain wave = wind surfing over ridges, lenticular clouds mark the wave tops