Why does the weather suddenly cool down?

In winter, the land temperature is lower than the ocean temperature, which forms a strong cold high pressure in the mainland, and the air flow diverges in all directions from the high pressure center. The air mass moving to low latitudes belongs to cold air mass in nature, and when it meets warm air mass, it forms a cold front. When the cold front crosses the border, it becomes rainy (snowy), windy and cool. After crossing the border, the temperature and humidity dropped sharply and the air pressure rose. In winter, the cold air mass moves southward rapidly (in the northern hemisphere, but in the southern hemisphere), which often leads to disastrous gale, cooling weather and even cold wave.