FAA Instrument Rating Airplane (IRA)Weather and Weather ServicesHard
A pilot planning a flight over a mountain ridge is briefed that surface winds aloft are forecast at 35 knots nearly perpendicular to the ridge line, with a stable air mass in place. Which hazard should the pilot be most prepared to encounter on the leeward side, and what visual cue might confirm its presence?
- AMicroburst activity, confirmed by a rapidly expanding cumulonimbus anvil
- BConvective turbulence, confirmed by towering cumulus clouds over the ridge
- CRadiation fog, confirmed by low stratus forming in the valley at dawn
- DMountain wave turbulence, confirmed by lenticular and rotor clouds downwind of the ridge
Show answer & explanationAnswer & explanation
Correct answer: D. Mountain wave turbulence, confirmed by lenticular and rotor clouds downwind of the ridge
Strong winds (generally greater than 25 knots) blowing perpendicular to a mountain ridge in a stable atmosphere commonly produce mountain wave activity on the leeward side. Lenticular (cap and wave) clouds and rotor clouds are visual indicators of this wave pattern, which can produce severe turbulence and strong up/downdrafts even in clear air.
Why the other options are wrong
- A. Microbursts are associated with convective thunderstorm activity, not stable mountain wave conditions.
- B. Convective turbulence requires an unstable air mass, not the stable conditions described.
- C. Radiation fog requires calm winds and clear skies at night, not strong winds aloft.
Mountain Wave Turbulence
Turbulence generated when strong winds flow perpendicular to a mountain ridge in a stable atmosphere, creating oscillating wave patterns downwind, often visualized by lenticular and rotor clouds.
- Requires stable air and strong perpendicular wind (>25 kt)
- Lenticular clouds mark wave crests
- Rotor clouds near the surface indicate severe turbulence zones
Memory trick: Strong wind + stable air + ridge = wave and rotor clouds.