What Causes Turbulence? A Complete Guide

What Is Turbulence?

Turbulence is irregular air movement that causes an aircraft to experience sudden changes in altitude or attitude. It happens when the smooth flow of air (laminar flow) is disrupted by temperature differences, wind shear, obstacles, or atmospheric instability.

Despite how it feels in the cabin, turbulence is a normal part of flying through Earth’s atmosphere. The atmosphere is a fluid — it has currents, eddies, and waves, just like an ocean. Your plane is a boat on that ocean.

The Five Types of Flight Turbulence

1. Clear-Air Turbulence (CAT)

Clear-air turbulence is the most common type encountered at cruising altitude and the hardest to detect. It occurs in cloud-free air, making it invisible to both pilots and weather radar.

What causes it: CAT is produced by wind shear at the boundaries of the jet stream. The jet stream is a narrow river of fast-moving air at 30,000–40,000 feet, often exceeding 150 knots. Where the jet stream’s edge meets slower-moving air, the sharp speed difference creates turbulent eddies.

Where it happens: Most commonly over the mid-latitudes (30°–60°N), where the polar jet stream flows. In the US, this means transcontinental routes and the East Coast corridor are most affected, especially in winter.

How it’s predicted: NOAA’s HRRR model detects CAT using diagnostics like the Ellrod Turbulence Index (TI-2), which identifies regions of strong wind deformation and convergence.

2. Convective Turbulence

Convective turbulence is associated with thunderstorms and other forms of atmospheric convection. It is the most intense type of turbulence a commercial aircraft can encounter.

What causes it: When the sun heats the ground unevenly, warm air rises in powerful updrafts. These updrafts can reach speeds of 50+ knots inside a cumulonimbus cloud, with corresponding downdrafts nearby. The chaotic mixing of rising and sinking air produces severe turbulence.

Where it happens: Most common in the Southeast US, Gulf Coast, and Great Plains from May through September. Also occurs along cold fronts and squall lines year-round.

How it’s predicted: Convective turbulence is the most predictable type. Weather radar shows active storms, and models like HRRR forecast convective parameters (CAPE, reflectivity, vertical velocity) hours in advance.

3. Mountain Wave Turbulence

Mountain wave turbulence is caused by air flowing over elevated terrain. It can produce some of the strongest turbulence encountered by commercial aviation.

What causes it: When stable air is forced up and over a mountain range, it creates wavelike oscillations on the leeward (downwind) side. These waves can propagate vertically to 40,000+ feet and horizontally for hundreds of miles downwind. Where the waves break (like ocean waves crashing), severe turbulence results.

Where it happens: The Rocky Mountains are the primary source in the US. The Sierra Nevada, Cascades, and Appalachians also generate mountain waves, though less frequently. Strongest when winds blow perpendicular to the ridgeline at 30+ knots.

How it’s predicted: Mountain waves are visible in high-resolution models like HRRR (3 km) because they produce patterns in the wind and temperature fields. Lenticular clouds (lens-shaped clouds) are a visible indicator of mountain wave activity.

4. Wake Turbulence

Wake turbulence is caused by the wingtip vortices of other aircraft. It is not weather-related but is an important source of turbulence, especially during approach and departure.

What causes it: Every aircraft generates two counter-rotating vortices trailing from its wingtips. These vortices are strongest behind heavy, slow, “clean” (no flaps) aircraft — exactly the configuration during approach. The vortices can persist for several minutes and drift with the wind.

Where it happens: Near airports, especially on approach and departure. Air traffic control maintains separation standards specifically to avoid wake turbulence. It is rarely encountered at cruising altitude because aircraft are widely separated.

How it’s predicted: Wake turbulence is managed through ATC separation standards, not weather forecasting. Pilots are trained to recognize and avoid wake turbulence situations.

5. Mechanical Turbulence

Mechanical turbulence is caused by air flowing over surface obstacles like buildings, terrain features, and vegetation. It’s most relevant during takeoff and landing.

What causes it: Surface friction disrupts the smooth flow of air in the lowest few thousand feet of the atmosphere (the boundary layer). On windy days, the disrupted air creates bumpy conditions during the climb-out and approach phases.

Where it happens: Near airports, especially those surrounded by uneven terrain, urban areas, or near coastlines where land and sea breezes create friction differences.

Factors That Affect Turbulence Intensity

Jet Stream Position and Strength

The jet stream is the single most important factor for clear-air turbulence. It shifts seasonally — stronger and farther south in winter, weaker and farther north in summer. When the jet stream is directly over your route, CAT is more likely.

Temperature Contrast

Turbulence thrives on temperature differences. Strong contrasts between air masses (e.g., a cold front meeting warm, moist Gulf air) create the instability that drives convective turbulence.

Wind Speed and Direction

High winds, especially those changing direction or speed with altitude (wind shear), are a direct cause of turbulence. The HRRR model measures wind shear at multiple pressure levels to detect this.

Time of Day

Convective turbulence peaks in the afternoon when solar heating is strongest. Early morning flights over the Southeast and Great Plains are typically smoother because convection hasn’t had time to develop.

Season

Winter = more CAT (stronger jet stream). Summer = more convective turbulence (more thunderstorms). Fall is generally the smoothest season for US domestic flights.

How Turbulence Is Forecasted

Modern turbulence forecasting relies on numerical weather prediction models — computer simulations of the atmosphere that solve the equations of fluid dynamics.

NOAA’s HRRR (High-Resolution Rapid Refresh) model is the gold standard for short-range turbulence prediction in the US. It runs every hour at 3 km resolution and forecasts up to 18 hours ahead. InflightScore uses the HRRR model to evaluate an ensemble of 11 independent scientific diagnostics along your flight route:

1. Turbulent Kinetic Energy (TKE) — measures chaotic air motion
2. Wind Shear — detects speed/direction changes between atmospheric layers
3. Ellrod Index (TI-2) — identifies CAT from jet stream dynamics
4. Convective Activity — flags thunderstorm-related turbulence

The Bottom Line

Turbulence has multiple causes, and understanding them helps demystify the experience. Clear-air turbulence is the most common at altitude. Convective turbulence is the most intense but also the most predictable. Mountain waves are terrain-dependent. And all of them are well within what your aircraft is designed to handle.