Turbulence encountered by aircraft when flying through air space devoid of clouds. Thermals and wind shear are the main causes.

strong turbulence in an otherwise cloudless region that subjects aircraft to violent updrafts or downdrafts

Turbulence encountered by aircraft when flying through air space devoid of clouds. Thermals and windshear are the main causes of clear-air turbulence; and recent studies have shown correlation between the position of the jet stream and reported occurrences of high-altitude clear-air turbulence.

(Abbreviated CAT.) A higher altitude (6–15 km) turbulence phenomenon occurring in cloud-free regions, associated with wind shear, particularly between the core of a jet stream and the surrounding air. It is most common near upper air fronts and the tropopause, and can often affect an aircraft without warning. Clear-air turbulence also frequently occurs close to towering cumulus clouds (usually within 30 km), and near mountains. Airflow disrupted by mountains and other terrain can undulate in waves of turbulence for 1000 km or more. See also aircraft turbulence.

Clear-Air Turbulence (often abbreviated CAT and sometimes colloquially referred to as "air pockets") is the erratic movement of air masses in the absence of any visual cues (such as clouds). Clear-Air Turbulence is caused when bodies of air moving at widely different speeds meet; at high altitudes (7,000-12,000 metres/23,000-39,000 feet) this is frequently encountered around jet streams or sometimes near mountain ranges. Clear-Air Turbulence is impossible to detect either with the naked eye or with radar, meaning that it is difficult to avoid.