Definition
An elongated area of relatively low atmospheric pressure extending from the center of a low-pressure system. On a weather chart, it appears as a stretched-out region where pressure is lower than the surrounding air, often associated with cloudiness, precipitation, and unsettled weather.
Plain English
A long, narrow band of lower-than-surrounding air pressure. Weather along this band is usually unsettled, often with clouds, rain, or thunderstorms.
Context Anchor
You may see this term in area forecasts, weather briefings, and weather charts when the forecast is explaining why clouds, rain, wind changes, or unsettled conditions are expected along a route.
Derivation
‘Trough’ comes from the Old English ‘trog,’ meaning a long, hollow container. The word is used here in the same shape sense — a long, dipped-out region, but in pressure rather than wood or metal.
Why Pilots Care
Low pressure troughs often bring unsettled weather including clouds, precipitation, turbulence, and shifting winds that affect flight planning and safety.
Analogy
Think of a weather map like a landscape of pressure. A low pressure trough is like a long shallow valley in that landscape, not a single deep hole.
Grounding Statement
Picture the pressure pattern across a region as a landscape of hills and valleys; a trough is a long valley of low pressure stretching out from the deepest low.
Intuition Check
Do not think of a trough as a ditch on the ground or a single storm point. In aviation weather, it means a long zone of lower pressure in the atmosphere.
Example Sentence 1
The Area Forecast called for scattered thunderstorms along a low pressure trough moving east through the afternoon.
Example Sentence 2
Checking the surface chart, the pilot noted the low pressure trough aligned with the frontal boundary and adjusted the flight plan accordingly.