when a cold front overtakes a warm front
As the storm intensifies, the
rotates around the storm and catches the
warm front. This forms
an occluded front, which is the boundary that
separates the new cold air mass (to the west) from the older cool air
mass already in place north of the warm front.
Symbolically, an occluded front is represented by a solid line with
alternating triangles and circles pointing the direction the front is
moving. On colored weather maps, an occluded front is drawn with a
solid purple line.