A big "H" on a map indicates High Pressure. That means heavy, descending air. Air circulates around a High in a clockwise fashion (in the northern hemisphere). The barometer rises as the High approaches. It is usually difficult for clouds to form. So a High usually brings fair weather. A big "L" on the map signifies Low Pressure. If the big "L" is approaching, a storm is coming! Low Pressure means that air is rising. Rising air is unstable, so clouds form and eventually rain or snow may develop. Hurricanes are intense areas of Low Pressure. The barometer falls as the Low approaches. Fronts usually are connected to Lows. Air circulates counterclockwise around a Low (in the northern hemisphere).