A pressure system is a region of the Earth's atmosphere where air pressure is a relative peak or lull in the sea level pressure distribution.The surface pressure at sea level varies minimally, with the lowest value measured 870.0 hectopascals (25.69 inHg) and the highest recorded 1,085.7 hectopascals (32.06 inHg).ain articles: Low-pressure area and Cyclone. A low-pressure area, or low, is a region where the atmospheric pressure at sea level is below that of surrounding locations. Low-pressure systems form under areas of wind divergence that occur in upper levels of the troposphere.