Wind Shear

What is Wind Shear?

Wind shear refers to a rapid variation in wind speed and/or direction across a relatively small vertical or horizontal distance. It can occur at any altitude but is especially critical at low levels (below 1600 ft AGL), where aircraft have limited time and altitude to recover from unexpected deviations.

Types of Wind Shear

• Vertical Wind Shear: Change in horizontal wind speed or direction with height. Commonly encountered when climbing or descending through layers with different wind characteristics, such as temperature inversions or near jet streams.
• Horizontal Wind Shear: Change in wind speed or direction over a horizontal distance at the same altitude. This is experienced when flying through gust fronts, microbursts, or along frontal boundaries.

Causes and Locations

Wind shear can form in various meteorological settings:

• Thunderstorms and Microbursts: Intense downdrafts and outflows create severe, localized wind shear.
• Frontal Zones: Sharp wind changes occur along cold and warm fronts.
• Temperature Inversions: Wind speed often increases rapidly just above the inversion layer.
• Terrain Effects: Hills, mountains, and buildings disrupt airflow, causing turbulence and wind shear downwind.
• Sea Breezes and Land Breezes: Convergence zones at coastal areas can produce low-level wind shear.

Effects on Aircraft

Sudden wind changes can cause abrupt gains or losses in airspeed and altitude. For example, encountering a decreasing headwind or increasing tailwind on approach can lead to a rapid loss of lift and possible descent below the glide path. Vertical currents can also cause uncommanded altitude changes, while crosswind shear can push the aircraft off the intended track.

Detection and Avoidance

• Detection: Modern airports use Doppler radar, wind sensors, and pilot reports to identify wind shear. Warnings are broadcast via ATIS or directly from ATC.
• Avoidance: Pilots should study weather reports, avoid flying near thunderstorms or frontal boundaries, and be prepared for wind shear on approach or departure, especially in known risk areas.

Wind Shear Intensity

Wind shear is categorized by the rate of wind change per 30 meters (100 ft):

• Light (0-4 KT), Moderate (5-8 KT), Strong (9-12 KT), Severe (>12 KT).

Areas of Worst Wind Shear

• Near thunderstorms and microbursts
• Frontal boundaries
• Over or downwind of mountainous terrain
• In and just above low-level temperature inversions
• Coastal convergence zones

Understanding wind shear and its operational implications is essential for safe flight and is a frequent focus in ATPL meteorology exams.