Definition
A weather front along which the boundary between two air masses of different temperature and humidity is moving very slowly or not at all, typically at speeds of less than about 5 knots. Neither air mass is displacing the other with any significant force, so the front lingers in roughly the same location, often producing extended periods of cloudiness and precipitation in the area beneath it.
Plain English
A boundary between two different air masses that is barely moving. Because it sits in one place for a long time, the weather it brings — clouds, rain, low ceilings — can stay over the same area for hours or even days.
Context Anchor
Seen on surface weather charts, aviation forecasts, and weather briefings when a front is expected to linger near an airport or along a planned route.
Derivation
From Latin 'quasi' meaning 'as if' or 'almost,' combined with 'stationary' from Latin 'stationarius' meaning 'standing still.' So the term literally means 'almost standing still' — which is exactly what this kind of front does.
Why Pilots Care
Persistent weather along the front can create extended periods of low ceilings, reduced visibility, or icing that affect route and timing decisions.
Grounding Statement
Picture a long line of weather lying across your route and barely moving, so flying later may not make the weather improve quickly.
Intuition Check
Do not read “stationary” as perfectly motionless. A quasi-stationary front can still drift; the key idea is that it is moving so slowly that the weather pattern stays in roughly the same place.
Example Sentence 1
The briefer pointed out a quasi-stationary front draped across the route, warning that the low ceilings would likely persist through the next day.
Example Sentence 2
Before filing the IFR plan the pilot checked whether the quasi-stationary front had begun to move.