Low pressure systems typically arrive with storminess and cloudiness, which is due to heating and expanding of the air mass. Air motion is usually upwards, as heated are is less dense and more buoyant than cooler air. A high pressure system is typically cooler than its counter-part, and skies are usually clear. This is due to sinking and cooling of it's air mass, since cool air is less dense than warm air. Low pressure systems carry more water vapor due to rising hot air cooling and condensing, while high pressure systems are much drier due to hot air sinking and cooling.
