barometric swamp

A meteorological situation characterised by the presence of an almost uniform pressure field over an extensive stretch of territory. It is easy to identify on a surface chart, since it corresponds to an area free of isobars, where atmospheric pressure values are relatively low, with barely any differences from one place to another, except those due to differences in ground elevation. Under a barometric swamp situation, skies are clear and ideal conditions exist for using and calibrating an altimeter, owing to the small oscillations experienced by pressure and its almost nil horizontal gradient.