Mountain and Valley Breezes

Like the land and sea breezes, mountains and the surrounding valleys also have breezes called Mountain and Valley Breezes. They are co-related localized winds that occur daily, one after the other. However, they are opposite to each other also.

During the day, the sun warms the air along the mountain slopes, more than the air near the valley, and the warm air becomes light as it reduces in density and a low pressure is formed at the top of the mountain. To fill the resulting gap, the air from the valley below forces a cool breeze to move upward. This condition generates a breeze that blows from the valley floor up towards the top of the mountain, creating a valley breeze, also known as valley wind.

The process is reversed at night when during the night, cool and dense air of the mountain slopes slides down to descend the valley below, producing a mountain breeze or mountain wind.

During the night, the air at the upper slope of the mountain cools off quicker than the valley below. As the slopes become cool, the air in the region become cool and dense, and high pressure is created. During that time, the air on the valley floor is a lot warmer and lighter. So it is forced to give way to the colder air, and the cold and dense air from the upper slope descends into the valley as the mountain wind.