What is the scientific basis for the long rain and drought?

When the weather is fine for a long time, the water vapor content in the air is generally low, so it is not easy to form fog. If there is fog, it means that the warm and humid air mass has moved from other places, and the weather may turn cloudy. On the contrary, in rainy weather for a long time, although the air is humid, it is still not easy to form fog because the clouds cover the sky and the temperature will not drop sharply. If there is fog, it means that the cold air has moved, and the rainy weather will soon end and turn fine.