weather front cold front 2019-08-20T16:53:00Z envoAtmo A weather front which is nonoccluded and which moves in the direction of the warmer air mass it is adjacent to, such that colder air will occupy the site where warmer air was previously present. The direction of motion determines whether fronts are "cold", "warm", etc. A front is said to be cold if it's moving in the direction of the warmer air mass it is adjacent to. From the perspective of an observer on the ground, this appears as though the colder air "replaces" the warmer air mass.