What does it mean that the morning fog is clear and the evening fog is cloudy?

Generally, morning fog indicates clear weather; fog during the day and night means continuous rain in the future. Because the former is radiation fog, and the latter is mostly advection fog.

The folk proverb goes well: "The fog is clear in the morning, cloudy in the evening, and drizzles in the evening. To know the sky accurately, you must To see what the weather is like before the fog, as the saying goes: "It will be sunny and foggy and rain for a long time, and it will be rainy and foggy for a long time and it will be clear." "This is because the weather has been clear for a long time and the air contains less moisture. Although the temperature drops at night, heavy fog generally does not occur. If heavy fog suddenly appears, it is probably due to the intrusion of warm and humid air, forming advection fog, which indicates the weather It will turn cloudy and rainy. On the contrary, there is plenty of moisture in the air after the rain, but due to the cloud cover (like covering the earth with a quilt), the ground heat is not easy to dissipate, and the ground does not cool down significantly at night, and it is not easy to form fog. Heavy fog appeared in the early morning of the next day. This was typical radiation fog. It was because the clouds in the sky broke up at night, causing the ground to cool down significantly, resulting in heavy fog. To accurately know the weather, you must look at the concentration of fog. Radiation fog is formed by the condensation of water vapor in the surface air, so it is relatively light, and the blue sky can be seen through the fog layer; while advection fog is formed by the cooling of a large area of ??warm and humid air, so it looks thicker. Therefore, people draw the conclusion: "If the fog is light, the sky will be fine; if the fog is thick, there will be strong winds; if the fog is heavy, it will rain heavily; if the fog is light, it will be sunny the next day."