The boundary between two air masses is called a front. Fronts can be stationary, warm, occluded or cold and often affect the weather on Earth.
Cold fronts cause warmer air to be pushed up, over the top of the colder air. The cold air remains close to the ground and eventually, the warmer air cools. Warm fronts also rise above cooler air. Because of the instability of the two air masses colliding, warm fronts often bring with them rain and thunderstorms.
Stationary fronts occur when a cold air mass and warm air mass meet, but both of them are too weak to overtake the other. Because two air masses of different temperatures meeting often cause rain and storms, a stationary front can cause heavy rain and flooding until one front gathers enough power to push the other out of the way.
An occluded front is more complicated than the others, because three air masses are involved. An occluded front happens when a warm front is caught between two cold fronts. The cooler fronts, because of their weight and density, move under the warm front and push it higher up.
Any of these fronts have the capability to cause dramatic weather changes such as temperature swings, high winds, rain, hail and severe weather.