What do you think of cold and warm fronts in geography?
Before crossing the border: controlled by a single air mass, the weather is fine;
Transit: cloudy, windy, rainy and snowy, cooling down.
After crossing the border: the temperature drops, the air pressure rises and the weather turns fine.
Warm front: blowing from high temperature area to low temperature area. Before crossing the border, the warm front was controlled by a single cold air mass, with low temperature and high pressure and sunny weather. After crossing the border, it is controlled by a single heating mass, with high temperature and low pressure and fine weather.
Before crossing the border: controlled by a single air mass, the weather is fine.
On the way: continuous precipitation
After crossing the border: the temperature rises, the air pressure drops and the weather turns fine.