Generally unfavorable weather conditions are associated with a low pressure area. In a low pressure area, the atmospheric pressure is low compared to the pressure of nearby areas, and the air tends to be unstable.
In this type of system, humid air rising from the surface of the Earth often produces rain or snow. Conditions are cloudy, and thunderstorms are possible. High winds are also a factor in low pressure areas, and tropical storms and tornadoes are a danger.
Typical air pressure is different in various regions. Areas in which low pressure is commonly found are between the equator and 10 degrees of latitude north and south and the area located around 60 degrees of latitude north and south. Low pressure areas, however, can and do form in other places as well.