If you live near or in mountainous areas you most certainly have experienced mountain and valley breezes. During calm and clear weather these wind events in mountainous terrain become quite noticeable starting in the morning and evenings with a definite wind reversal.
These increases in wind speed are driven by unequal heating and cooling of the valleys and mountains in the area. This daily thermal cycle circulation works like this.
During the day, sunlight warms the land and air in the Valley and along the slopes of the mountains. 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. The cooler and denser air at higher elevations flows back down the slopes of the mountain and into the valley. This is called a mountain breeze.
For Weather Nation: Meteorologist Mike Morrison