Lee Waves will form if the wind direction is within _____ of perpendicular to the ridge.

Lee waves are a type of atmospheric wave that forms on the leeward side of a mountain ridge when stable air flows over the ridge. The formation of these waves requires specific wind conditions, particularly concerning its direction relative to the ridge.

When the wind is perpendicular to the ridge, it leads to the most efficient transfer of energy and wave formation. The correct answer indicates that lee waves will form when the wind direction is within 30 degrees of being perpendicular to the ridge. This narrow angle ensures that the airflow is unobstructed and allows for the development of the pressure differences on either side of the ridge, which is necessary for the creation of wave patterns in the atmosphere.

Other options suggest wider angles which would not create the optimal conditions for the formation of lee waves. As the angle widens, the wind becomes less aligned with the ridge, reducing the ability for stable air to create the necessary oscillations and pressure differentials characteristic of lee waves. Hence, having a specified range of 30 degrees reflects the precise conditions needed for these phenomena to develop effectively.