Lee waves are a type of atmospheric wave that forms on the downwind side of a mountain or hill when stable air flows over the terrain. As the air rises over the peak, it cools and creates a wave pattern in the atmosphere. These waves can extend for long distances and are often visible as cloud formations. When the air descends on the other side, it can create a series of oscillations, leading to alternating areas of rising and sinking air. Lee waves can influence weather patterns and are important for understanding phenomena like mountain waves and turbulence in aviation.