What are air masses?

Air masses are large bodies of air that have similar temperature, humidity, and stability characteristics throughout. They form over a source region, which can be over land or water, and can cover thousands of square miles. Air masses are classified based on their temperature and humidity characteristics, with the main types being continental (dry) and maritime (moist), as well as polar, tropical, and arctic. When air masses move and interact with each other, they can cause changes in weather patterns.

Air masses are large bodies of air with fairly uniform temperature and moisture properties. They originate over large relatively flat areas of the Earth's surface where the air remains for several days, acquiring distinct temperature and moisture characteristics from the underlying surface. Air masses form over source regions and then move with the prevailing wind patterns. As they move, they may modify somewhat by taking on the characteristics of the surfaces over which they pass. The source regions are usually large bodies of water (ocean or lake) or flat land having uniform vegetative cover.