An air mass is a batch of air that has a uniform temperature and humidity. An air mass acquires these characteristics from the land or water that it is above. Air masses are very large and form in high-pressure zones such as polar and tropical regions. Temperate regions are too unstable for air masses to form, creating unique weather in these areas.
Air masses move when they are pushed by high-powered winds. Once they move, they gain new characteristics based on the area they are positioned over.
Storms are caused when an air mass moves over a region with different characteristics. For example, warm air masses moving over cold landmasses cause storms. Cold air masses tend to flow towards the equator and warm air masses tend to flow toward the poles. This helps balance the temperature of the earth.