Final answer:
Low-pressure systems occur when the earth's surface atmospheric pressure is lower than the surrounding environment. The air rising aloft and the associated low-pressure regime can be found in areas where warm air meets cold air.
Step-by-step explanation:
In terms of weather, low-pressure systems occur when the earth's surface atmospheric pressure is lower than the surrounding environment: Moist air rises and condenses, producing clouds. Movement of moisture and air within various weather fronts instigates most weather events. The air rising aloft and the associated low-pressure regime can be found in areas where warm air meets cold air, such as in the vicinity of weather fronts or along the Intertropical Convergence Zone (ITCZ).