Wind shear

Wind shear is a difference in either wind speed or direction over a fairly short distance in the atmosphere. Wind shear can be divided into two different types: horizontal and vertical wind shear.

NASA schematic of the downward motion of the air until it hits ground.

When wind shear is observed

Weather situations when the Wind shear is observed happen:

At weather fronts when the temperature difference across the front is 5 °C or more, and the front moves at 15 kt or faster.
At low level jets when a significant low level vertical wind shear can develop near the lower portion of the low level jet.
At mountains when winds blow over and create vertical shear on the lee side.^[1]
At inversions when on a clear and calm night a radiation inversion is formed near the ground.
At downbursts when an outflow boundary moves away from a thunderstorm.
At sailing when wind shear affects sailboats by presenting a different wind speed and direction at different heights along the sailing mast.

Wind Shear Media

Cirrus uncinus ice crystal plumes showing high-level wind shear, with changes in wind speed and direction
Down draft winds with associated virga allow these clouds in the eastern sky at civil twilight to mimic aurora borealis in the Mojave desert.
Wind shear along the coast with low-level clouds moving towards the east and higher-level clouds moving towards the south-west
Strong wind shear in the high troposphere forms the anvil-shaped top of this mature cumulonimbus cloud, or thunderstorm.
Depiction of where the planetary boundary layer lies on a sunny day
Glider ground launch affected by wind shear
Effect of wind shear on aircraft trajectory. Note how merely correcting for the initial gust front can have dire consequences.
Wreckage of Delta Air Lines Flight 191 tail section after a microburst slammed the aircraft into the ground. Another aircraft can be seen flying in the background past the crash scene.
Hodograph plot of wind vectors at various heights in the troposphere. Meteorologists can use this plot to evaluate vertical wind shear in weather forecasting. (Source: NOAA)