A mountain breeze is wind that travels down from a mountain to a valley. Areas where there are mountains and valleys have a certain type of wind pattern known as mountain and valley breezes.
Mountain breezes occur at night because the mountain slopes cool the air, causing high pressure as the air becomes densely packed. The high pressure pushes the wind down the mountain. Valley breezes occur during the day as the air over the mountain slope warms up. The warm air's density goes down, and a low pressure is created near the mountain top. The cool air below causes high pressure and forces air to move upward. This is common during warm months.