In reference to clear air turbulence (CAT), which areas should be avoided based on horizontal wind shear?

Clear air turbulence (CAT) often occurs in regions where there are significant changes in wind speed, known as wind shear. The correct answer highlights the threshold of horizontal wind shear to be avoided, which is essential for maintaining safe flight operations.

Horizontal wind shear is defined as a change in wind velocity over a horizontal distance. In this case, a wind shear of 40 knots per 150 miles indicates a substantial gradient and potential for turbulence. This type of shear can lead to unexpected and severe turbulence, particularly at higher altitudes where CAT is most frequently encountered.

Understanding this threshold is crucial for pilots and dispatchers in flight planning and routing. Avoiding areas with this significant horizontal wind shear helps mitigate the risk of encountering CAT, which can result in sudden altitude changes and passenger discomfort, as well as potential structural stress on the aircraft.

The other options present lower thresholds of wind shear which may still be significant but are less critical in terms of anticipating serious turbulence. Those lower thresholds do not indicate as high a risk of CAT as the criterion that has been deemed correct, making the understanding of this particular threshold particularly important for safety in aviation.