Trough (meteorology)

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

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, it is a dotted line. If it is not marked, troughs may still be identified as an extension of isobars away from a low pressure center.

Sometimes, the region between two high pressure centers may assume the character of a trough when there is a detectable wind shift noted at the surface. In the absence of a wind shift, the region is designated a col, akin to a geographic saddle between two mountain peaks.

If a trough forms in the mid-latitudes, a temperature difference between two sides of the trough usually exists in the form of a weather front. A weather front is usually less convective than a trough in the tropics or subtropics (such as a tropical wave). Sometimes, collapsed frontal systems will...
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