Trough

A trough is an elongated area of relatively low atmospheric pressure, extending from the centre of a low-pressure system. On a surface analysis chart, it appears as a V-shaped or U-shaped extension of isobars from a low-pressure centre. Troughs are associated with weather disturbances, wind shifts, and precipitation.

Trough Weather

The passage of a trough is often accompanied by: a wind shift (backing before, veering after, in the Northern Hemisphere), increasing cloud and precipitation, a brief pressure fall then rise, and sometimes convective activity. In summer, a surface trough (heat trough) over land can trigger afternoon thunderstorm development along the trough axis.

Upper-Level Troughs

At upper levels, troughs in the jet stream flow are associated with cold air advection and upward motion on their downstream side — triggering surface cyclone development and weather. The shortwave trough is a smaller embedded disturbance within the larger flow that moves through upper-level troughs.

Related Terms

See also: Shortwave Trough, Cold Front, Jet Stream.