Wind shear is a phenomenon describing highly localized variability in wind speed and/or wind direction. Because wind shear can affect the angle of attack on an airfoil (e.g., the wing, or control surfaces of an airplane) wind shear can cause a loss of lift or control. Dangerous to aviation, wind shear is particularly hazardous when encountered during take-off or landing.

Wind shear is the difference in speed or direction between two layers of air in the atmosphere. Wind shear may occur in either a vertical or horizontal orientation. An example of the former situation is the case in which one layer of air in the atmosphere is traveling from the west at a speed of 31 mph (50 km per hour) while a second layer above it is traveling in the same direction at a speed of 6.2 mph (10 km per hour). The friction that occurs at...