When two air masses collide, a front is formed. The two most common types of fronts are cold fronts and warm fronts.
Cold fronts are formed by the advance of cold continental polar or continental arctic air towards the south. The colder air wedges underneath the warmer air mass to the south and causes it to rise, forming a storm front.
A warm front is the pushing action done by an advancing mass of maritime tropical warm and moist air that pushes a colder air mass out of the way by rising on top of it gradually and moving it away slowly. This causes an extensive cloud front of light rains.
