Wind Shear

Wind shear describes situations in which wind changes speed and/or direction along the horizontal and/or vertical axis. Changes along the vertical axis are known as vertical wind shear, while changes along the horizontal axis are known as horizontal wind shear.

Wind shear is a major hazard, especially for flights operating at low levels (below 500 m or approximately 1600 ft). Wind shear can affect flight performance in various ways. A headwind gust will increase aircraft speed and force an aircraft to accelerate and/or fly above its intended path.

Example of how low level wind shear with a sudden strong headwind affects landing

Wind shear due to updrafts and downdrafts (the most dangerous kind) can displace an aircraft upward or downward. A tailwind gust will decrease aircraft speed and force it to fly below its intended path and/or decelerate.

Exemple de la façon dont un cisaillement de vent dans les basses couches avec un vent arrière fort et brusque affecte l'atterrissage

Finally, crosswind shear can make an aircraft drift laterally away from its intended flight path.

Ce croquis montre comment le cisaillement du vent affecte un avion. Les courants descendantes sont un danger pour les avions, notamment au décollage et à l'atterrissage.

The WMO criteria for forecasts of hazardous low-level windshear/turbulence require that one or more of the following be met: