Definition
A temperature inversion that occurs at a frontal boundary when a layer of warm air rides up over a layer of colder air near the surface, producing a zone in which temperature increases with altitude instead of decreasing.
Plain English
When a warm air mass slides over a colder one along a front, you end up with cold air near the ground and warmer air above it. That backwards temperature setup is a frontal inversion.
Context Anchor
Seen in aviation weather study and weather briefings when fronts, low clouds, fog, or widespread steady precipitation are being discussed.
Derivation
Frontal comes from front, the boundary between two air masses. Inversion comes from the Latin invertere, meaning to turn upside down. Together the term describes a temperature pattern that has been turned upside down at a frontal boundary -- warm air sitting on top of cold air, which is the reverse of the normal pattern.
Why Pilots Care
Frontal inversions can trap moisture, promote icing, reduce visibility, and create smooth or turbulent layers that affect climb performance and approach planning.
Grounding Statement
Picture cold air pooled at the surface with a warm air mass gliding up and over it -- the air gets warmer as you climb through that boundary, not cooler.
Intuition Check
“Frontal” does not mean the front of the airplane; it means a weather front. “Inversion” does not mean the aircraft is upside down; it means the normal temperature pattern is upside down.
Example Sentence 1
The briefer warned of a frontal inversion ahead of the warm front, which was likely producing the low ceilings and light freezing drizzle reported along the route.
Example Sentence 2
With the frontal inversion in place the pilot expected smoother air once above the surface layer but reduced visibility in trapped moisture.