There are two possible occurrences when air masses collide, which are frontal wedging and convergence. Frontal wedging creates a temperature-based weather front, and convergence is the process that leads to the formation of clouds.
When two air masses come into contact with each other, their temperatures determine what happens. The way in which air works, cool air lowers to take the place of warm air as the warm air rises. If a warm mass of air moves and collides with a cool mass of air, then a warm front is created. In the opposite situation, a cold front is created. There are situations when the two masses press against each other, and neither moves.
The other occurrence caused by the collision of two air masses is the creation of clouds. For this event to happen, the air masses have to meet two requirements. The first requirement is that the air masses are the same temperature. The second requirement is that neither air mass is willing to move away from the other. When these two conditions are met, the air masses begin to move upwards instead of trying to move through each other until they come together and create a cloud.