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Turbulence, particularly clear air turbulence, is a significant and often unexpected hazard to aircraft during flight.  Turbulent eddies with wavelengths of 10 m to 1 km are felt as bumpiness, say by aircraft flying at ~250 m s-1. Aircraft  Aircraft are more sensitive to vertical gusts than to lateral gusts.

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CATEDR

ecChart colours

(Fig8.1.14-1)

WeakNil<0.05 10 m2/3 s-1


Light blueModerate0.05 10 – 0.3 20 m2/3 s-1

Blue, dark Light blue,

green, yellow 


Moderate0.20 – 0.45 Strong to severe>0.3 m2/3 s-1

OrangeBlue, dark orangeblue,red, dark brown, purple

green, yellow 

Severe (observed example)>0.5 45 m2/3 s-1

Light purple and clear


Table8.1.14-1: Relationship between CAT descriptions and eddy dissipation rate (EDR) used in Cy50r1 (May 2026).  Standard ICAO (International Civil Aviation) turbulence classes.

In Cy50r1 (May 2026):

  • CAT is interpolated onto standard ICAO flight levels (FL).  These have been introduced as a new Mars level type:  50/60/70/80/90/100/110/120/130/140/150/160/170/180/190/200/210/220/230/240/250/260/270/280/290/300/310/320/330/340/350/360/370/380/390/400/410/420/430/440/450 corresponding to the standard ICAO correspondence table from pressure levels to flight levels.
  • The calibration of CAT has been improved, notably the prediction of the moderate to severe turbulence classes,  based on an updated climatology of aircraft data.  More information on this available. 


An example of clear air turbulence

Fig8.1.14-1: ecChart of energy dissipation rate. DT 12UTC 2 March 2023, VT 03UTC 3 March 2023.  Colours given in Table81Table8.1.14A. Note: HRES and Ensemble Control Forecast are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast output is equivalent to HRES output shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.


Fig8.1.14-2: ecChart of 300 hPa contours (dam).  300hPa winds (kt) shown as arrows and isotachs (coloured). DT 12UTC 2 March 2023, VT 03UTC 3 March 2023. Severe CAT values of EDR to the east of the strongest jet and extend into the unshaded area enclosing winds below 50kt.  Pin shows Dallas, Texas.  Severe turbulence was encountered by an aeroplane in this system causing emergency diversion to an available airfield. 

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