Trough and Ridge

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As you may know, a jet stream is a fast moving current of air encircling the globe that serves to steer storm systems and transport air masses poleward and equator ward. Embedded within the jet stream are numerous upper level "troughs" and "ridges." When looking at the long wave pattern, troughs and ridges are large undulations that represent rising and falling upper level heights - or more simply, pockets of warm and cold air.

A trough is officially defined as an elongated area of relatively low atmospheric pressure - or a region of lower atmospheric heights. As atmospheric heights and pressure correlate to temperature, low heights correspond to cold air. A trough, or dip, in the jet stream often implies unsettled weather and cool temperatures. The reverse is true for a ridge. A ridge is an elongated area of relatively high atmospheric pressure and represents a region of higher upper level heights and thus, typically, a pocket of warmer air in the atmosphere.