The weather on planet Earth changes constantly. One reason is because the winds are always shifting, rising, falling and creating areas of various pressure in the atmosphere. A high-pressure system is one of these results of the shifting winds. This type of system means the pressure inside the system is higher than that of the surrounding areas.
High-pressure systems are usually associated with fair weather. This is because as the air sinks, it warms and is able to hold more water vapor. Thus, in these systems, clouds tend to evaporate and the air stabilizes. Storms have a hard time forming in stable air.
The humidity is usually lower in or near a high-pressure system, also contributing to fair weather. Many desert areas of the world are associated with a persistent high-pressure climates. The drier air helps create the desert environment.
Although most people like the weather that comes with this type of system, it isn't all good. Heat waves and drought conditions come about because of several high-pressure systems moving through an area, or because of a prolonged system that will not move out of an area. In fact, meteorologists hypothesize that the Dust Bowl of 1930s America, with its droughts and heat, was caused by a persistent high-pressure system trend across the Midwest and through Arkansas and Oklahoma.
Sometimes, a particular area will become associated with a high-pressure system. In the summer, those living in the Southeastern U.S. are familiar with the Bermuda High phenomenon. This is a system that tends to be long-lived, contributing to the summer heat. The clockwise windflow around a high-pressure system also ensures the moisture coming from the Gulf of Mexico moves across the area, creating the high humidity for which the area is infamous.
This type of system can also cool the weather. Those in the United States are also familiar with the winter Siberian Express and Alberta Clipper systems that bring in Arctic or Canadian cool air and cause cold snaps.