Why does frosting always happen on sunny mornings?

The colder the winter morning, the more frost there is. The reason is that the relative temperature is high during the day, which is related to thermal radiation. On sunny days, the earth's heat will quickly spread to outer space, while on cloudy days, the cloud can reflect the inverse heat back to the earth and play a role in heat preservation, so the relative temperature difference between day and night is small. On a sunny day, water vapor will condense into solids at night, and these solids are frost.

The above is purely my own statement, and my expression level is limited, so it is not very smooth. Ha, anyway, as long as you understand the meaning,