FAA Airline Transport Pilot (ATM)Transport Aerodynamics and High-Altitude OperationsMedium
A flight crew is briefed that moderate-to-severe clear air turbulence (CAT) is forecast near their cruise altitude of FL350. This turbulence is most likely to be associated with which meteorological feature?
- ACumulonimbus buildups embedded in a warm front
- BOrographic lifting over mountainous terrain far below
- CStrong wind shear near the core of a jet stream
- DConvective activity from surface heating below the flight path
Show answer & explanationAnswer & explanation
Correct answer: C. Strong wind shear near the core of a jet stream
Clear air turbulence at high altitude, in the absence of visible convective clouds, is most commonly caused by strong horizontal and vertical wind shear associated with jet streams, particularly on the low-pressure (poleward) side near the tropopause. This is why jet stream charts and turbulence forecasts are closely correlated for high-altitude cruise planning.
Why the other options are wrong
- A. Cumulonimbus-associated turbulence is convective, not 'clear air,' since it occurs within visible clouds.
- B. Mountain wave/orographic turbulence typically affects lower to mid altitudes near terrain, though it can extend upward it's not the primary CAT source at cruise.
- D. Surface convective heating primarily affects lower altitudes, not FL350 cruise turbulence.
Clear Air Turbulence (CAT)
CAT is turbulence occurring in cloud-free air at high altitude, most commonly caused by strong wind shear associated with jet streams near the tropopause.
- Occurs without visual cues (no clouds)
- Strongest near jet stream cores and tropopause breaks
- Forecast using turbulence charts correlated with jet stream position
Memory trick: Jet stream shear, turbulence near