What group controlled the weather before the cold front crossed the border?

Controlled by the warm air mass, it was sunny and warm before the cold front crossed the border.

The front formed by the active movement of the cold air mass to the warm air mass is called the cold front (as shown in the left picture). Cold front is the most common front in China, which controls most areas in winter. Before the cold front moved to a certain place, a certain place was controlled by a warm air mass, and the weather was sunny and warm. When the cold front moves to a certain place, the warm air here is lifted to high altitude by the cold air near the surface, and the water vapor condenses, forming rainy weather, accompanied by strong winds and cooling. After the cold front moved over, a place was controlled by a cold air mass, the temperature dropped and the weather turned fine.