Turbulence is irregular air motion that causes an aircraft to move unpredictably. It's caused by several distinct atmospheric phenomena — some predictable, some invisible, some unavoidable. Here's the complete explanation.
The jet stream is a narrow band of fast-moving air at cruise altitude, typically 30,000–40,000 feet. It flows from west to east across the North Atlantic and North Pacific, reaching speeds of 100–200 mph. When an aircraft crosses the jet stream boundary — flying from slow air into fast air or vice versa — the wind shear creates turbulence. This is why transatlantic routes are consistently bumpy in winter (jet stream strongest December–March) and smooth in summer. Westbound flights that fight the jet stream spend more time in the wind-shear zone and are typically rougher than eastbound flights riding the same stream.
When wind flows over a mountain range, it creates waves on the downwind (lee) side that can extend to cruise altitude and beyond. Mountain wave turbulence (also called orographic turbulence) is predictable because it occurs whenever strong winds meet a mountain range — the Andes in South America, the Rockies in North America, the Alps in Europe, and the Himalayas in Asia. Andes crossings (Santiago–Buenos Aires, Santiago–Mendoza) consistently produce the world's highest turbulence scores because the Andes reach 22,000+ feet and create massive wave systems. Rocky Mountain approaches (Denver from the west, Aspen, Jackson Hole) experience the same effect at a smaller scale. Mountain turbulence is detectable from weather models and gives pilots advance warning.
Cumulonimbus (CB) clouds — thunderstorms — generate extreme updrafts and downdrafts that extend from near the ground to well above cruise altitude. Convective turbulence near CB cells is the most intense type — EDR values near large thunderstorms can reach 0.8+ (extreme). Pilots use weather radar to detect and route around CB cells. Tropical routes have higher convective turbulence risk: Caribbean hurricane season (June–November), Southeast Asian monsoon (May–October), and sub-Saharan Africa (year-round). In the US, summer convection over the Midwest (April–September) creates turbulence on domestic routes.
Every aircraft generates wing-tip vortices — rotating cylinders of air that trail behind it. These vortices can be violent enough to roll a following aircraft if it flies through them. Wake turbulence rules require minimum spacing between aircraft (3–6 minutes behind a heavy aircraft). On final approach and departure, wake turbulence is carefully managed by air traffic control. At cruise altitude, wake turbulence dissipates quickly and affects other aircraft only in rare cases. If you feel a sudden single jolt in cruise — sometimes described as 'hitting a wall' — it may be a wake turbulence encounter.
Ranked by historical turbulence score — click any route for details