FAA Instrument Flight Instructor (FII)WeatherHard
A pilot planning a high-altitude flight near a strong jet stream asks a CFII where clear air turbulence (CAT) is most likely to be encountered relative to the jet core. Which location is correct?
- ADirectly within the jet core where the maximum wind speed occurs
- BOn the polar (cold) side of the jet stream near the tropopause, where wind shear is greatest
- COn the equatorial (warm) side, well below the tropopause, where wind speed is minimum
- DOnly below the jet stream in the stratosphere, unrelated to wind shear
Show answer & explanationAnswer & explanation
Correct answer: B. On the polar (cold) side of the jet stream near the tropopause, where wind shear is greatest
CAT is most commonly associated with strong horizontal and vertical wind shear found on the polar (cold) side of the jet stream near the tropopause, particularly where the jet curves sharply or where wind speed changes rapidly along its length.
Why the other options are wrong
- A. The jet core itself has strong wind but relatively uniform flow; shear (not raw speed) drives turbulence, which is greatest at the edges.
- C. Wind shear, and thus CAT potential, is weaker on the warm side where speed gradients are less pronounced.
- D. CAT is directly tied to jet stream wind shear near the tropopause, not isolated to the stratosphere.
Clear Air Turbulence (CAT) and the Jet Stream
CAT is turbulence occurring in clear air, often associated with strong wind shear near the tropopause on the cold (polar) side of the jet stream, especially where the jet curves or changes speed abruptly.
- Jet stream: narrow band of strong winds near the tropopause
- CAT strongest where wind shear is greatest, not where wind speed is highest
- Cold/polar side of jet has the sharpest shear
- Cirrus clouds ('mares' tails') can be a visual clue to jet stream location
Memory trick: Shear, not speed, shakes the plane — look to the cold side of the jet