Turbulence » Introduction Intensity of Turbulence

There are four different levels of turbulence intensity defined by the aviation community:
1. Extreme turbulence:
Violent bumping of the aircraft, occasionally resulting in significant structural damage and
loss of control.
Relatively rare occurrence, fortunately, and generally confined to the lee
of mountain ranges at relatively low levels in the vicinity of a rotor cloud (see photo), when
the cross-barrier wind component is greater than 50 knots, or in severe thunderstorms associated
with squall lines.
2. Severe turbulence:
Sudden large changes in aircraft altitude, airspeed, and attitude, occasionally leading to
temporary loss of control.
May be found in mountain waves where the cross-barrier wind component is 25-50 knots.
In these cases, turbulence may occur from ridgetop level to a few thousand feet (1000 m) above,
for up to 50 miles (80 km) to the lee of the range. If the cross-barrier component exceeds 50 knots,
the severe turbulence layer be as deep as 5000 feet (1525 m), extending up to 150 miles (240 km) to the
lee of the range. Severe turbulence can also occur near thunderstorms and in strong horizontal and
vertical wind shear environments, extending above and below, as well as up to 100 miles (160 km)
poleward of an upper-level jet stream core.
3. Moderate turbulence:
Sudden, frequent bumpiness of the aircraft but little or no variations in aircraft altitude or attitude.
4. Light turbulence:
Light bumpiness, little more than a nuisance to aircraft operators.