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Effect of Obstructions on Wind

by Flight Learnings

in Weather Theory

Another atmospheric hazard exists that can create problems for pilots. Obstructions on the ground affect the flow of wind and can be an unseen danger. Ground topography and large buildings can break up the flow of the wind and create wind gusts that change rapidly in direction and speed. These obstructions range from manmade structures like hangars to large natural obstructions, such as mountains, bluffs, or canyons. It is especially important to be vigilant when flying in or out of airports that have large buildings or natural obstructions located near the runway. [Figure 11-15]

Figure 11-15. Turbulence caused by manmade obstructions.

Figure 11-15. Turbulence caused by manmade obstructions. -Click to Enlarge-

The intensity of the turbulence associated with ground obstructions depends on the size of the obstacle and the primary velocity of the wind. This can affect the takeoff and landing performance of any aircraft and can present a very serious hazard. During the landing phase of flight, an aircraft may “drop in” due to the turbulent air and be too low to clear obstacles during the approach.

This same condition is even more noticeable when flying in mountainous regions. [Figure 11-16] While the wind flows smoothly up the windward side of the mountain and the upward currents help to carry an aircraft over the peak of the mountain, the wind on the leeward side does not act in a similar manner. As the air flows down the leeward side of the mountain, the air follows the contour of the terrain and is increasingly turbulent. This tends to push an aircraft into the side of a mountain. The stronger the wind, the greater the downward pressure and turbulence become.

Figure 11-16. Turbulence in mountainous regions.

Figure 11-16. Turbulence in mountainous regions. -Click to Enlarge-

Due to the effect terrain has on the wind in valleys or canyons, downdrafts can be severe. Before conducting a flight in or near mountainous terrain, it is helpful for a pilot unfamiliar with a mountainous area to get a checkout with a mountain qualified flight instructor.

515G+mn0RuL._SX331_BO1,204,203,200_Learn more about aviation weather with Weather Flying by Robert Buck. Regarded as the bible of weather flying, this aviation classic not only continues to make complex weather concepts understandable for even the least experienced of flyers, but has now been updated to cover new advances in technology.


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