METRO (Meteorology) – VT-10 Primary Practice Test 2026 - Free Meteorology Practice Questions and Study Guide

When two air masses collide and the cold front catches up to the warm front, the boundary becomes an occluded front on the weather map. This is shown with a purple line because purple signals a combination of the warm and cold boundaries. Along that line you’ll see alternating symbols of triangles and semicircles on the same side, indicating the presence of both cold and warm air meeting at the same boundary. The movement direction is conveyed by the line’s orientation, but the key visual cue is the purple line with both shapes on one side. The other depictions describe only a cold front (blue triangles on a line) or only a warm front (red semicircles on a line), which do not capture the merged boundary of an occlusion. A purple line with just circles isn’t a standard front symbol.