High pressure systems can be cold or warm, humid or dry. The origin of a high-pressure region determines its weather characteristics.
If a high-pressure system moves into Wisconsin from the south during the summer, the weather is usually warm and clear. If the high pressure originates from the north, it will generally bring cold or cooler weather.
When high pressures form, they adopt the characteristics of the source regions over which they form. Cold, high-pressure air masses form in polar regions, and are called polar air masses. Warm air masses are of subtropical or tropical origin; both are referred to as tropical air masses.
Air masses that form over water are referred to as maritime, whereas those generated over continents are referred to as continental. Maritime air masses are usually moister than continental air masses formed at the same latitude.
Atmospheric pressure is greater in a high-pressure system than the surrounding areas. High-pressure areas at ground level are normally caused by air above that is moving downward. This sinking air, called subsidence, is bad for cloud formation, so high pressure systems often have few clouds.
You may have also noticed that the winds are light when we are under the influence of a high pressure. The lack of wind causes pollutants to build up in the high, leading to reduced air quality. Few clouds also mean good sunshine that, along with the warm temperatures in the summer, is good for ozone formation at the ground.
