Locating Aviation Turbulence

Areas listed below are probable locations of turbulence, by intensity category, and the associated weather and terrain features. This information is taken from the old Pilot Weather Briefer Course.

Light Turbulence

Weather and terrain features associated with light turbulence:

1. In hilly and mountainous areas with light winds
2. In and near small cumulus clouds
3. In clear-air convective currents over heated surfaces
4. With weak wind shears in the vicinity of:
   Troughs aloft
   Lows aloft
   Jet streams
   The tropopause
5. In the lowest 5,000 feet of the atmosphere:
   When winds are near 15 knots
   Where the air is colder than the underlaying surface

Moderate Turbulence

Weather and terrain features associated with moderate turbulence:

1. In mountainous areas with a wind component of 25 to 50 knots perpendicular to and near the level of the ridge:
   At all levels from the surface to 5,000 feet above the tropopause with preferences for altitudes:

   Within 5,000 feet of the ridge level

   At the base of relatively stable layers below the base of the tropopause

   Within the tropopause layer
   Extending outward on the lee of the ridge for 150 to 300 miles
2. In and near thunderstorms in the dissipating stage
3. In and near other towering cumuliform clouds
4. In the lowest 5,000 feet of the atmosphere:
   When surface winds exceed 25 knots
   Where heating of the underlying surface is unusually strong
   Where there is an invasion of very cold air
5. In fronts aloft
6. Where:
   Vertical wind shears exceed 6 knots per 1,000 feet, and/or
   Horizontal wind shears exceed 18 knots per 150 miles

Severe Turbulence

Weather and terrain features associated with severe turbulence:

1. In mountainous areas with a wind component exceeding 50 knots perpendicular to and near the level of the ridge:
   In 5,000 feet layers:

   At and below the ridge level in rotor clouds or rotor action

   At the tropopause

   Sometimes at the base of the other stable layers below the tropopause
   Extending outward on the lee of the ridge for 50 to 150 miles
2. In and near growing and mature thunderstorms
3. Occasionally in other towering cumuliform clouds
4. 50 to 100 miles on the cold side of the center of the jet stream, in troughs aloft, and in lows aloft where:
   Vertical wind shears exceed 6 knots per 1,000 feet, and
   Horizontal wind shears exceed 40 knots per 150 miles

Extreme Turbulence

Weather and terrain features associated with extreme turbulence:

1. In mountain wave situations, in and below the level of well-developed rotar clouds. Sometimes it extends to the ground.
2. In growing severe thunderstorms (most frequently in organized squall lines) indicated by:
   Large hailstones (3/4 inch or more in diameter)
   Strong radar echoes, or
   Almost continuous lightning