A cold front.
Depending on how they collide, it can result in a tornado. But if it were to just simply replace the warm air mass, it would just be a cold front.
a warm front
A cold front develops, often resulting in precipitation, and sometimes thunderstorms.
A cold front.
The point where these two air masses meet is called a front.If cold air advances and pushes away the warm air, it forms a cold front.When warm air advances, it rides up over the denser, cold air mass to form a warm front.If neither air mass advances, it forms a stationary front.
The warm air mass is pushed up and the weather becomes cool and stormy.
when warm air meets cool air and either one don't move its called a stationary front
Cold
A cold front is the transition zone were a cold air mass replaces a warm air mass. A warm front is a transition zone were a warm air mass replaces a cold air mass.
What happens is similar to when a warm air mass meets a cold air mass: the Cold Air Mass is forced to Subside beneath the Warm Air Mass. Thusly the warm air is uplifted, it cools and Rain is formed. When a Warm Air Mass meets a Cold Air Mass, the warm air is [again] forced to Rise above the Cold Air Mass, it cools and Rain is formed.
Cold
Cold