High pressure and Low pressure

                  

High Pressure:

Pressure is important to the earth's atmosphere because is can determine wind and weather patterns across the globe. High pressure areas are caused by air masses being cooled, from above or from below. As the air mass cool it shrinks. As it shrinks things around the air mass will fill in above it. Hight pressure areas are usually fair, sunny weather. Because air shrinks when there is high pressure you are often left with clear sunny skies. 

Low Pressure:

Low pressure areas are generally cloudy and rainy areas. Low pressure is an area of rising air, it then condenses in to clouds and rain. If you have high and low pressure in the same place you will have windy weather and the wind will blow between the two air masses.