Where does the air mass originate?

How are air masses formed in this context?

When air is left to stagnate for long periods of times on a flat surface, it forms air masses. The surface on which they form determines the characteristic temperature and moisture. These attributes are acquired by an air mass through heat and moisture interactions with the surface.

How are air masses defined in meteorology? An air mass in meteorology is defined as a volume of air that is determined by its temperature and water vapour content. The air masses span many hundreds of miles and adjust to the conditions of the ground below. They are classified according their latitude and the continental or maritime origin regions.

This is how cold air masses are created.

The air masses of continental polar (cP), or continental arctic, are stable, cold, and dry. Radiational cooling causes these air masses to originate above northern Canada and Alaska. They then move eastward, eastward and eastward into the Plains, and then eastward.

Which region is best for an air mass?

An ideal source area for an air mass is: flat areas with uniform composition and light surface winds. Northern Canada and Alaska are the sources of cP or cA air mass that enter the United States.