FAA Flight Instructor Airplane (FIA)Weather and Weather ServicesMedium
A pilot is briefed for a flight over mountainous terrain where winds of 40 knots are forecast to blow nearly perpendicular to a mountain ridge, with a stable atmosphere aloft. Which cloud formation would most strongly suggest the presence of mountain wave turbulence?
- AA solid overcast layer of nimbostratus
- BTowering cumulus building in a line along the ridge
- CScattered cirrus uncinus streaming from the west
- DStanding lenticular altocumulus clouds downwind of the ridge
Show answer & explanationAnswer & explanation
Correct answer: D. Standing lenticular altocumulus clouds downwind of the ridge
Mountain wave turbulence occurs when strong stable winds flow perpendicular to a mountain range, creating oscillating wave patterns downwind. Standing lenticular altocumulus clouds, along with rotor clouds, are the classic visual indicators of this phenomenon, remaining stationary in appearance despite strong winds.
Why the other options are wrong
- A. Nimbostratus indicates widespread stable precipitation, not the wave pattern associated with mountain waves.
- B. Towering cumulus in a line suggests instability and convective activity, not stable mountain wave conditions.
- C. Cirrus uncinus (mare's tails) indicate high-altitude wind shear but are not specific to mountain wave activity.
Mountain Wave Turbulence
Turbulence occurring downwind of mountain ranges when strong stable winds flow perpendicular to the terrain, creating oscillating wave patterns.
- Requires strong wind (typically 25+ kt) roughly perpendicular to the ridge
- Stable atmosphere is necessary for wave formation
- Indicated by standing lenticular clouds and rotor clouds near the surface
Memory trick: Lenticular clouds look like flying saucers parked over the mountains