Clear-air turbulence (CAT) is turbulence that occurs in cloudless skies with no visible warning. It's invisible to weather radar, impossible to see from a cockpit window — and it's increasing. Here's everything you need to know.
Clear-air turbulence (CAT) occurs outside of clouds, typically at cruise altitude (28,000–45,000 feet), where fast-moving jet stream air meets slower-moving air. The boundary between these air masses — called wind shear — creates invisible eddies and vortices that aircraft fly through without warning. Unlike convective turbulence (caused by thunderstorms), CAT produces no visual or radar signature. Pilots cannot see it, their weather radar cannot detect it, and it appears without warning. CAT is most intense just below the jet stream core, in the troposphere near the tropopause.
Standard aircraft weather radar works by detecting water droplets — it bounces microwave energy off precipitation and clouds. Clear-air turbulence has no water content; it's dry air moving at different velocities. There's nothing for the radar to reflect off. This is why severe CAT can occur in perfectly clear blue sky. Technologies that can detect CAT include Doppler lidar (which measures air particle velocity — available on some newer aircraft) and EDR (eddy dissipation rate) sensors that detect turbulence after flying through it and relay the data to other aircraft. TurboTrack aggregates EDR data from thousands of flights daily to build a real-time map of where CAT is occurring.
A landmark 2023 study in Geophysical Research Letters (Williams & Joshi, University of Reading) found that severe clear-air turbulence over the North Atlantic increased by 55% between 1979 and 2020. The mechanism: climate change is strengthening the temperature gradient between the tropics and the poles, which intensifies the jet stream. A stronger jet stream creates more wind shear and more CAT. Projections suggest severe North Atlantic CAT will increase by 149–188% by 2100 under high-emissions scenarios. This means passengers in coming decades will encounter significantly more rough air on transatlantic routes.
Ranked by historical turbulence score — click any route for details