cold air masses have lower or higher air pressure
It has more molicules....
Yes. Cold air masses have higher density, because the molecules are closer together. That makes them have higher pressure because there is more mass per unit volume pressing down. The molecules are...
The warm air mass is forced to rise, creating convection and precipitation.
Cold air is more dense than warm air. This is why cold air masses tend to descend, and warm air masses tend to rise.