How do valley breezes move

The warmer and less dense air near the ground rises during the day pulling more air through the valley floor. This gentle upslope wind known as a valley breeze. The flow of air reverses as the sun is going down and at night. This is because the mountain slopes at higher elevations cool quicker than the valleys.

rising temperatures because when water vapor in the air is cooled, it condenses. it turns back into a liquid and attaches to dust particles in the air. these very small water droplets group together to form clouds