Aviation In Canada

Sunday, January 02, 2005

High Winds & Turbulence

Going flying? Would you like a smooth ride? Did you notice the winds outside as you drove to the airport? If they're strong on the surface, you can bet they're strong aloft and probably not lose. Want another sure bet? Bumps in the lower levels.

Mechanical turbulence is its name. When the wind cruises along and hits trees, hills, even buildings, it gets churned up. Especially if it hits a small range of hills or cliffs. The wind has nowhere to go but up, where it disturbs the winds in the levels above it. All of this creates turbulence. 20 knots (~40km/h) of wind on the surface is good for moderate turbulence up to 3,000 or so above ground level, even in relatively flat terrain.

Now look at a real mountain range like the Rockies. If the winds are strong enough, you can get the Mountain Wave effect. When this happens, you can get little bubbles of air caught between wind levels, creating a strong rolling effect. These can be very dangerous for light aircraft, producing a rolling moment strong enough that the aircraft can't counter, thereby leading to an uncontrolled flip. Even airliners would do well to avoid them, if only for a smoother ride. Sometimes clouds will form in the bubbles, and these will help you avoid them. If the winds are strong enough, they can persist for several tens of miles, even a hundred or so, downrange from the mountains. Stay away from these areas when it's windy.