FAA Instrument Flight Instructor (FII)WeatherMedium
A pilot is briefed that winds of 35 knots are forecast to blow perpendicular to a mountain ridge with a stable air mass in place, and standing lenticular altocumulus clouds are reported downwind of the ridge. What should the pilot expect?
- AWidespread advection fog forming over the ridge
- BMountain wave turbulence, potentially severe, with strong up- and downdrafts
- CSmooth, laminar airflow with no significant turbulence hazard
- DA temperature inversion that will prevent any turbulence from developing
Show answer & explanationAnswer & explanation
Correct answer: B. Mountain wave turbulence, potentially severe, with strong up- and downdrafts
Strong wind flow perpendicular to a mountain ridge in a stable air mass produces mountain wave activity downwind of the terrain. Standing lenticular clouds are a visual indicator of this wave pattern, which can produce severe turbulence, strong up/downdrafts, and possible rotor turbulence at lower altitudes.
Why the other options are wrong
- A. Advection fog requires warm moist air over a colder surface, not the wind/stability conditions described.
- C. Lenticular clouds specifically indicate wave motion, not smooth laminar flow.
- D. A stable air mass actually favors wave formation and turbulence, rather than preventing it.
Mountain Wave Turbulence
Mountain wave turbulence forms when strong winds blow perpendicular to a mountain ridge in a stable air mass, creating oscillating wave patterns downwind that can produce severe turbulence and strong vertical currents.
- Requires strong wind (often >25kt) roughly perpendicular to the ridge
- Occurs in stable air masses
- Standing lenticular clouds and rotor clouds are visual indicators
- Can cause severe turbulence and altitude excursions even at high altitudes
Memory trick: Lenticular clouds = frozen wave photos of turbulent air