Why does the weather forecast say that when cold air passes, the fog will disperse?

Fog proves that the local area is controlled by a warm air mass, and the warm and humid airflow is strong, generally blowing southeast wind or southwest wind, so there will be fog.

The source of cold air in China is mostly in the north, generally moving from north to south. Cold air is dry and cold in nature. When cold air passes through the border, it means that this place will be controlled by cold air mass, and the air will become dry and cold. When crossing the border, the north wind will blow more and the wind will be stronger (because there is a pressure difference with warm air, the greater the pressure difference, the greater the wind).

Therefore, the dry and cold northerly wind blowing when the cold air passes through the border will suppress the warm and humid airflow in the south, which is locally controlled by the cold air mass, dry and cold, and does not have the conditions to form fog (the formation of fog depends on water vapor, temperature, wind and other conditions. ), the natural fog will disperse.