Question

what causes a valley breeze

Answer 1

Mountain and valley breezes form through a process similar to sea and land breezes. During the day, the sun heats up mountain air rapidly while valley remains relatively cooler. Convection causes it to rise, causing a valley breeze. At night, the process is reversed.

Answer 2

In days, the sunlight heats up the mountains while winds in valleys remain cool. It causes convection and valley breeze. At night this process is opposite.