Glossary

Low Pressure System

Credit
Pearson Education Inc.

Surface air flows outwards (diverges) from an area of high pressure (H) and spirals counterclockwise into a low pressure system (L). Converging surface air is forced to rise, cooling as it does so. If sufficient moisture is present, cloud formation occurs followed by subsequent precipitation.

Low pressure systems generate cloudy skies, precipitation, and, over time, drastic changes in temperature and wind. Air flows from areas of high pressure to areas of low pressure, spiraling inwards and upwards in a counterclockwise manner, resulting in atmospheric lift. 

An area of relatively low atmospheric pressure surrounded on all sides by higher pressure is referred to as a low. An elongated area of low pressure extending from a low is called a trough.