JPATS Weather - NETC
JPATS Weather - NETC
JPATS Weather - NETC
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<strong>JPATS</strong> AVIATION WEATHER BOOKLET<br />
Frontal Turbulence<br />
Figure 4-5 — Frontal Turbulence<br />
Frontal turbulence is caused by lifting of warm air by a frontal surface leading to instability, or<br />
by the abrupt wind shift between the warm and cold air masses. The vertical currents in the warm<br />
air are the strongest when the warm air is moist and unstable. The most severe cases of frontal<br />
turbulence are generally associated with fast moving cold fronts. In these cases, mixing between<br />
the two air masses, as well as the differences in wind speed and or direction (wind shear), add to<br />
the intensity of the turbulence.<br />
Ignoring the turbulence resulting from any thunderstorm along the front, Figure 4-5 illustrates<br />
the wind shift that contributes to the formation of turbulence across a typical cold front. The<br />
wind speeds are normally greater in the cold air mass.<br />
Wind Shear Turbulence<br />
Large-scale wind shear turbulence results from a relatively steep gradient in wind velocity or<br />
direction producing eddy currents that result in turbulence. Wind shear is defined as a sudden<br />
change in wind speed or direction over a short distance in the atmosphere. The greater the<br />
change in wind speed and/or direction in a given area, the more severe the turbulence will be.<br />
These turbulent wind shear flight conditions are frequently encountered in the vicinity of the jet<br />
stream, where large shears in both the horizontal and vertical planes are found, as well as in<br />
association with land and sea breezes, fronts, inversions, and thunderstorms. Strong wind shear<br />
can abruptly distort the smooth flow of wind, creating rapid changes in aircraft performance.<br />
Version 3.2/Dec 08 4-7
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