Why is it foggy in the morning and sunny all day?

During the day, the sun shines on the ground, and the ground accumulates a lot of heat. Because of the evaporation of water, the air with higher temperature can hold more water vapor, so there is more water vapor in the air. After the sun went down, heat began to radiate into the air, and the air temperature near the ground also decreased. The better the weather, the less clouds in the sky, and the heat on the ground is not hindered. The faster the radiation, the lower the air humidity. By midnight and morning, the temperature of the ground air has dropped very low. At this time, even indoors, we can easily feel that it is much colder in the middle of the night. When the temperature near the ground drops, the water vapor in the air exceeds the saturation state, and the excess water vapor condenses into tiny water droplets, which are distributed at low altitude. This is what meteorology calls "radiation fog". This kind of fog usually appears near the center of high pressure, and it is often sunny near the center of high pressure. So when this fog appears, although it is all foggy in the morning, as long as the sun comes out and evaporates the fog, it will mostly be sunny.