erratic air currents that occur in cloudless air between altitudes of 7,000 and 12,000 metres (23,000 and 39,000 feet) and constitute a hazard to ... [1 related articles]
[n] - strong turbulence in an otherwise cloudless region that subjects aircraft to violent updrafts or downdrafts
noun strong turbulence in an otherwise cloudless region that subjects aircraft to violent updrafts or downdrafts
atmospheric turbulence, sometimes severe, occurring in air devoid of clouds or other visible indicators that turbulence might be present. Abbr.: CAT