An air mass is a large volume of air that exhibits relatively uniform characteristics of temperature, moisture, and pressure over a horizontal expanse. These properties are initially acquired from the surfaces over which the air mass forms and may be further influenced as it traverses different regions. Weather patterns are determined by the interactions of these air masses as they move across the Earth's surface.

Air masses are categorized based on their source regions, and their specific attributes depend on:

• The characteristics of the area where the air mass originates.
• The duration the air mass spends over its source region.
• Any alterations that occur to the air mass as it moves away from its source region.