What separates high- and low-pressure systems?
When it comes to air pressure, everything is relative. There is no threshold value that indicates high or low pressure. The only thing that separates centers of high and low pressure are regions that have lower pressure readings than the high — and higher pressure readings than the low. Since air pressure is essentially the weight of the atmosphere above a location, weather maps are drawn to compare air pressure readings at different locations. High-pressure systems usually form where the air converges aloft. As the air converges in the upper levels of the atmosphere, its own weight forces it to sink. The sinking air spirals outward, clockwise in the Northern Hemisphere, counterclockwise south of the Equator. Low-pressure systems often form where the air diverges aloft, allowing for air from lower levels to rise. As air rises, it cools and often condenses into clouds and precipitation. . There’s plenty more about highs and lows on this USA TODAY resource page.
