Turbulence when flying is one of the most common sources of passenger anxiety. Understanding exactly what causes it — and what actually happens to the aircraft — makes a real difference to how you experience it.
Turbulence can occur at any phase of flight, but follows predictable patterns: (1) Climb (0–20 min): the aircraft passes through the lower atmosphere where convective activity and weather systems are most active. Bumps here are typically brief and light. (2) Cruise (30,000–40,000 ft): the main source is clear-air turbulence (CAT) from jet stream wind shear. This is the phase with the most potential for sustained moderate turbulence on long routes. Typically peaks 2–4 hours into long-haul flights as the aircraft crosses the jet stream core. (3) Descent and approach: re-entering the active weather layer. Wind shear near the surface can cause abrupt bumps on final approach. Night flights tend to be slightly smoother because convective (thunderstorm) activity peaks in the afternoon.
A smooth flight happens when: (1) the jet stream is positioned away from your route, (2) there is no convective activity in the region, (3) the air mass is stable (high pressure). Summer mornings, night flights, and high-pressure weather systems produce the smoothest conditions. Routes over flat terrain (ocean crossings in calm seasons, tropical routes outside monsoon) are also naturally smoother. When you check in and the flight is forecast as smooth, it's because wind shear models show minimal vertical velocity gradients along the route.
Ranked by historical turbulence score — click any route for details