CLASSIFICATION AND INTENSITY OF TURBULENCE

The Airmans Information Manual, chapter 7, contains a turbulence reporting criteria table, which describes the meteorological characteristics with which the respective classes of turbulence are associated. Terminal Aerodrome Forecast (TAF) Code, NAVMETOCCOMINST 3143.1, lists code figures for turbulence type and intensity.

The Turbulence Reporting Criteria Table, table 5-2, has been adopted as the standard. All NAVMETOCCOM units must adopt these as standards as a guide in forecasting turbulence.

The following is a guide to the classification of turbulence.

This rarely encountered condition is usually confined to the strongest forms of convection and wind shear, such as the following:

. Mountain waves in or near the rotor cloud, usually found at low levels, leeward of the mountain ridge when the wind normal to the mountain ridge exceeds 50 knots.

. In severe thunderstorms where the production of large hail (three-fourths inch or more) is indicated. It is more frequently encountered in organized squall lines than in isolated thunderstorms.

Severe turbulence may also be found in the following:

When the wind normal to the mountain ridge exceeds 50 knots. The turbulence may extend to the tropopause, and at a distance of 150 miles leeward. A reasonable mountain wave turbulence layer is about 5,000 feet thick.

When the wind normal to the mountain ridge is 25 to 50 knots, the turbulence may extend up to 50 miles leeward of the ridge, and from the mountain ridge up to several thousand feet above.

. In and near mature thunderstorms, and occasionally in towering cumuliform clouds.

. Near jetstreams within layers characterized by horizontal wind shears greater than 40 knots/150 run, and vertical wind shears in excess of 6 knots/1,000 feet.

When such layers exist, favored locations are below and/or above the jet core, and from roughly the vertical axis of the jet core to about 50 to 100 miles toward the cold side.

When the wind normal to the mountain ridge exceeds 50 knots. Moderate turbulence may be found from the ridge line to as much as 300 miles leeward.

When the wind normal to the ridge is 25 to 50 knots, moderate turbulence maybe found from the ridge line to as much as 150 miles leeward.

. In, near, and above thunderstorms, and in towering cumuliform clouds.

. Near jetstreams and in upper level troughs, cold lows, and fronts aloft where vertical wind shears exceed 6 knots/1,000 feet, or horizontal wind shears exceed 10 knots per 100 miles.

. At low altitudes, usually below 5,000 feet, when surface winds exceed 25 knots, or the atmosphere is unstable due to strong insolation or cold advection.

In addition to the situations where more intense classes of turbulence occur, the relatively common class of light turbulence maybe found:

. At low altitudes when winds are under 15 knots, or the air is colder than the underlying surface.

This information is now available on CD in Adobe PDF Printable Format

Privacy Statement - Press Release - Copyright Information. - Contact Us - Support Integrated Publishing