Mountain waves are a type of atmospheric wave that occurs when strong winds blow over mountain ranges. As the air flows over the peaks, it can create a series of oscillations or ripples in the atmosphere, similar to waves in water. These waves can extend for long distances downwind of the mountains and can affect weather patterns and local turbulence. These waves are often associated with lee waves, which form on the downwind side of mountains. Pilots need to be aware of mountain waves, as they can create sudden changes in altitude and turbulence, making flying challenging in mountainous regions.