Fronts Fronts are boundaries between contrasting air masses One air masses is warmer than the other and therefore more bouyant. Where the two air masses meet the warmer, more bouyant air mass with be uplifted relative to the colder, more dense air mass. Because of their steep slope, air rises quickly, condenses and cause large rain storms but they are limited in areal extent. Stationary fronts are usually similar to a cold front in structure, but neither air masses have moved substantially. Occluded Fronts Occluded fronts seperate two polar air masses, with a colder air mass usually advancing on a slightly warmer air mass.
Occlusion refers to closure.
An occluded front describes the situation where a cold front cuts off a warm front from the surface. Here an advancing cold front takes over a slower moving warm front. A cold and warm type of occluded front. Surface pressure with fronts indicated. Note that all four types of fronts are shown here.