Synoptic scale

In meteorology, the synoptic scale (also called the large scale or cyclonic scale) is a horizontallength scale of the order of 1,000 km (620 mi) or more. This corresponds to a horizontal scale typical of mid-latitudedepressions (e.g. extratropical cyclones). Most high- and low-pressure areas seen on weather maps (such as surface weather analyses) are synoptic-scale systems, driven by the location of Rossby waves in their respective hemisphere. Low-pressure areas and their related frontal zones occur on the leading edge of a trough within the Rossby wave pattern, while high-pressure areas form on the back edge of the trough. Most precipitation areas occur near frontal zones.