What is the precursor of foggy days?

Hello, there is usually a lot of fog in autumn and winter mornings. It is usually very cold after fog, and the temperature is higher during the day, so the air can hold more water vapor. There is fog in the morning, and the temperature will rise after fog. It is foggy at night, because the temperature drops and the air is quite humid. When it cools to a certain extent, some water vapor in the air will condense out and become many small water droplets suspended in the air layer near the ground, so the fog will last for a long time, and then the temperature will drop.