Valley breezes are gentle winds that occur in mountainous regions, particularly during the daytime. They form when the sun heats the valley floor, causing the air to rise. As the warm air ascends, cooler air from the surrounding mountains moves in to replace it, creating a soft breeze that flows down into the valley. These breezes are most common in the summer months and can help moderate temperatures in the area. They are often associated with the mountain and valley topography, contributing to local weather patterns and influencing the climate of regions like the Sierra Nevada or the Appalachians.