Why is the temperature difference between sunny days smaller than cloudy days?

Under the condition of clear sky and cloudless Wan Li, the sun can directly shine on the earth without penetrating clouds during the day, so the temperature is higher, and the heat of the earth will be radiated at night, so there is more energy radiated without the blocking of clouds, so the temperature difference between day and night is larger. Rainy weather, clouds, blocking the energy of the sun during the day, the temperature is not high. At night, there is little energy radiation, little temperature drop and small temperature difference.