Definition
The boundary between two air masses of differing temperature and humidity that is not moving, or is moving very slowly (typically less than about 5 knots). Neither air mass is displacing the other, so the front remains in roughly the same place for hours or days. Weather along a stationary front is often persistent, with extended periods of clouds, rain, or low ceilings.
Plain English
A weather boundary between two different air masses that is sitting still instead of moving across the ground. Because it isn't moving on, the same area can get hours or days of similar weather.
Context Anchor
Pilots encounter stationary fronts in weather briefings, surface weather charts, and forecasts when checking whether weather along a route may stay in place.
Derivation
From Latin 'stationarius' meaning 'standing still.' The word 'front' was borrowed from military usage, where it described the boundary line between two opposing forces. A stationary front is literally a weather boundary that is holding its position.
Why Pilots Care
A stationary front often produces extended periods of clouds, rain, or fog that can affect visibility and force route changes or delays.
Analogy
A stationary front is like two teams in a tug-of-war that are evenly matched. The rope may wiggle, but the center line does not move much, so the same area keeps being affected.
Grounding Statement
Picture two air masses pressing against each other with equal force — neither one wins, so the boundary stays put and the weather along it lingers.
Intuition Check
Stationary does not mean the weather is calm or harmless. It means the boundary between the air masses is not moving much; clouds, rain, or poor visibility can still develop or persist near it.
Example Sentence 1
A stationary front lying across the route kept the destination below minimums for most of the afternoon.
Example Sentence 2
Because the stationary front lingered over the area, the instructor canceled the morning cross-country flight due to persistent reduced visibility.