Air pressure is the pressure exerted by atmosphere on the surrounding environment. Air pressure can affect the weather, depending on whether the pressure is high or low.
Barometric Pressure While factors like temperature, humidity and wind conditions play a big part in the weather an area might see, air pressure also has a big affect on whether a region experiences good or bad weather. The barometric pressure reading is affected by high-pressure and low-pressure areas within local and national weather patterns. Scientists and weathermen determine the air pressure at ground level in a given area by looking at the barometric pressure levels on an instrument called a barometer. An increase in the reading on the barometer signifies a rise in the air pressure, which leads to good weather, while a decrease in this reading means that the air pressure is falling, a clear signal that bad weather has arrived or is on the way. Typically, once a storm has moved through a region, the barometric pressure should begin to rise again.
High Pressure An area of high pressure occurs when the atmosphere over a given location is heavier, which forces the air above down, creating a divergence as the air moves out, away from the center of the high-pressure area. This, in turn, leads to clear skies overhead and creates a breeze that cools the surrounding area. High-pressure areas are more prevalent during the warmer months of the year and produce drier, more stable weather patterns.
Low Pressure In a low-pressure area, the air above it is lighter than the atmosphere below. This leads to a lifting of the air near the ground as it pushes against the area of reduced pressure above. This rising of the air leads to a convergence near the ground as air rushes in to fill the void left by the rising air. In addition, the rising air begins to cool, leading to the formation of clouds overhead, sometimes accompanied by rain or snow depending on the surrounding temperature. The colder months see more low-pressure zones as the colder air tends to weigh more, creating more pressure near the surface than above, which produces more unstable weather patterns, such as rain, snow, ice and wind.
Weather Events Caused by Air Pressure Where a high pressure and low-pressure areas meet are called fronts. It is at these fronts that more extreme weather can occur. A low-pressure area can cause extreme weather events like thunderstorms, blizzards and tornadoes. The type of weather generally depends on the time of year, with heavy thunderstorms and tornadoes occurring during the spring and summer, and blizzards and other winter weather occurring during the winter months. Some locations, like California and Florida, tend to have decent weather year round due to the higher pressure of the atmosphere along the coast, though sometimes storms do occur. In addition, the coastal areas, like Florida and along the East and West Coast, are more likely to suffer from extreme weather events like hurricanes during the summer and fall.