<P> Wind shear (or windshear), sometimes referred to as wind gradient, is a difference in wind speed and / or direction over a relatively short distance in the atmosphere . Atmospheric wind shear is normally described as either vertical or horizontal wind shear . Vertical wind shear is a change in wind speed or direction with change in altitude . Horizontal wind shear is a change in wind speed with change in lateral position for a given altitude . </P> <P> Wind shear is a microscale meteorological phenomenon occurring over a very small distance, but it can be associated with mesoscale or synoptic scale weather features such as squall lines and cold fronts . It is commonly observed near microbursts and downbursts caused by thunderstorms, fronts, areas of locally higher low - level winds referred to as low level jets, near mountains, radiation inversions that occur due to clear skies and calm winds, buildings, wind turbines, and sailboats . Wind shear has significant effects on control of an aircraft effect, and it has been a sole or contributing cause of many aircraft accidents . </P> <P> Wind shear is sometimes experienced by pedestrians at ground level when walking across a plaza towards a tower block and suddenly encountering a strong wind stream that is flowing around the base of the tower . </P>

Turbulence is likely when winds aloft have a shear of greater than