Trough (meteorology)

A trough is an elongated region of relatively low atmospheric pressure, often associated with fronts.

Unlike fronts, there is not a universal symbol for a trough on a weather chart. The weather charts in some countries or regions mark troughs by a line. In the United States, a trough may be marked as a dashed line. In the UK, Hong Kong and Fiji, it is represented by a bold line extended from a low pressure center or between two low pressure centers; in Macau and Australia, it is a dotted line. If they are not marked, troughs may still be identified as an extension of isobars away from a low pressure center.