The
synoptic scale in
meteorology (also known as
large scale or
cyclonic scale) is a horizontal length scale of the order of 1000 kilometres (about 620 miles) or more. This corresponds to a horizontal scale typical of mid-latitude
depressions (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 surface highs form on the back edge of the trough. Most
precipitation areas occur near frontal zones. The word
synoptic is derived from the Greek word (), meaning
seen together.