Definition
A line drawn on a weather chart along the axis of a trough — an elongated area of relatively low atmospheric pressure. The trough line marks where pressure is lowest along that axis, and it is typically associated with a wind shift, cloudiness, and unsettled weather as it passes.
Plain English
A line on a weather map showing the center of a long, narrow area of low pressure. As this line moves over an area, the wind usually shifts and the weather often turns cloudy or rough.
Context Anchor
Seen on aviation weather charts and discussed in weather briefings when a route may pass near unsettled weather.
Derivation
From the everyday word 'trough' — a long, narrow, dipped container (like a feeding trough). In meteorology, the air pressure 'dips' along an elongated path, and the line drawn through the lowest points of that dip is the trough line.
Why Pilots Care
Trough lines frequently bring clouds, precipitation, and turbulence that can affect routing and safety decisions.
Analogy
Think of air pressure like a landscape. A trough line is like the path along the floor of a long valley, where the pressure is lowest compared with the higher areas on both sides.
Grounding Statement
A trough line appears on charts as a dip in pressure that pilots avoid or plan around for smoother flight.
Intuition Check
Do not think of a trough line as a physical line on the ground or in the sky. It is a line on a weather chart showing the lowest-pressure path in a stretched-out low-pressure area; it is not automatically the same thing as a front.
Example Sentence 1
The briefer pointed out a trough line extending southwest from the low, warning of scattered showers along its path.
Example Sentence 2
By flying east of the trough line the crew avoided the band of low clouds and rain.