Definition
A type of occluded front that forms when a fast-moving cold front overtakes a slower-moving warm front, and the air behind the cold front is colder than the cool air ahead of the warm front. The colder, denser air wedges under the cool air, lifting the warm air aloft and producing a mix of cold front and warm front weather characteristics along the boundary.
Plain English
It happens when a cold front catches up to a warm front, and the air pushing in behind is even colder than the air it meets. That coldest air slides underneath, shoving the warm air up and out of the way and leaving a single boundary on the surface between the two cooler air masses.
Context Anchor
Seen in aviation weather study, weather briefings, and surface weather charts when learning how occluded fronts form and what weather they can bring.
Derivation
Occlusion comes from the Latin occludere, meaning to shut or close off. The warm air mass gets shut off from the surface as the colder air closes in beneath it. It is called a cold front occlusion because the air arriving behind the cold front is the coldest of the three air masses involved.
Why Pilots Care
The passage of a cold front occlusion typically brings a period of widespread low ceilings, reduced visibility, and possible icing, all of which affect route planning and safety.
Grounding Statement
Picture a dense, cold wedge of air sliding along the ground and forcing the warmer air ahead of it to rise.
Intuition Check
Do not read this as just “a cold front.” A cold front occlusion is an occluded front: it happens after a cold front catches a warm front and lifts the warm air off the ground.
Example Sentence 1
The briefer noted a cold front occlusion across the route, so the pilot expected lifted warm air aloft and a mix of cold and warm front weather along the boundary.
Example Sentence 2
During the preflight briefing the instructor pointed out that the cold front occlusion would bring a rapid drop in temperature once it passed the airport.