It is foggy in the morning, sunny at night and cloudy at night.

There is fog in the early morning and rain in the late morning, which means that the fog we see may indicate sunny days, but if the fog does not gather (late fog means that the fog is delayed until evening, that is, the fog lasts for a long time), it may turn into rainy weather.

We see the fog in the morning. If the sun comes out soon, the fog will dissipate. This is a feature of radiation fog, and it is of course sunny. However, there are exceptions. For example, on a clear and cloudless night, the breeze is slow, which is a good environment for generating radiation fog, and the ground temperature drops rapidly. Under the action of breeze and turbulence, the air in the near-surface layer is also cooled under the action of the surface, and the excess water vapor quickly condenses into small fog drops, so the fog in the sky quickly forms. After that, if a new weather system moves in, the sky will be covered with a thick layer of clouds, thus forming a situation of fog below and thick clouds above. After the sun comes out in the morning, because there are thick clouds above to block the sun, the ground can't heat up quickly, and the fog drops can't evaporate or rise quickly, which leads to fog failure. If the clouds don't close, it is possible that the fog will be cloudy at night. So if you see fog in the morning and it hasn't gathered after the sun comes out, you can foresee that there is already a thick layer of clouds in the sky, and the weather is likely to turn rainy in the future.