Definition
An occluded front is a weather front formed when a faster-moving cold front overtakes a slower-moving warm front, lifting the warm air mass off the surface so that two cooler air masses meet at ground level. On a surface analysis chart it is depicted in purple, with alternating triangles and half-circles pointing in the direction of frontal movement, both on the same side of the line.
Plain English
It is a front where a cold front has caught up with a warm front and squeezed the warm air upward, leaving cool air on both sides at the surface. On weather charts, it is drawn in purple.
Context Anchor
Seen on aviation weather charts that show front locations, including surface analysis and forecast weather charts.
Derivation
Occluded comes from the Latin occludere, meaning to shut up or close off. The warm air mass is closed off from the surface, lifted up between the two cooler masses below.
Why Pilots Care
These fronts often bring widespread clouds, reduced visibility, and areas of turbulence or icing that affect route planning and altitude choice.
Grounding Statement
Picture colder air catching up from behind and squeezing the warm air upward, leaving a purple front line on the chart where that weather change is happening.
Intuition Check
Occluded does not mean the front is hidden or gone. It means the warm air at the ground has been closed off and lifted by colder air.
Example Sentence 1
The briefer pointed to the occluded front shown in purple stretching across the route and recommended delaying the departure until it moved east.
Example Sentence 2
After the occluded front passed, the low-level moisture cleared and visibility improved for the return flight.