Measured by a barometer, the force that air exerts as it is being pulled to Earth by gravity.
Two kinds of air pressure systems:
High-pressure system (H on a weather map)
Low-pressure system (L on a weather map)
Watch the video to see how the air pressure system changes on a weather map.
High Pressure System
Surface air moves outward, and the air above sinks toward the ground.
The higher you go, the colder the temperatures get.
The air that sinks warms up.
Water droplets evaporate in the warmer air, which results in clear days.
Low Pressure System
Surface air moves toward the low pressure from all sides.
As it converges into one area, it is forced to rise.
The higher you go, the colder the temperatures get, and colder air holds less water vapor.
The vapor then condenses into water droplets that form clouds.
Results in cloudy days with rain or snow. Severe weather such as blizzards and hurricanes form as well.