North American Air Masses Explained

In North America, there are five distinct air masses. An air mass is an area of air with horizontally uniform temperature, humidity, and pressure.

Air masses cover many hundreds or thousands of kilometres and adapt to the characteristics of the surface below them.
 

Air masses are classified according to latitude and continental or maritime source regions.
 

Colder air masses are termed polar or arctic, while warmer air masses are deemed tropical. Continental air masses are dry while maritime air masses are moist.
 

The five air masses of North America are:

Continental Arctic

These air masses are cold, dry, and stable. These air masses originate over northern Canada and Alaska.
 

Maritime Polar

These air masses form over the northern Atlantic and the northern Pacific oceans. Maritime polar air masses can form any time of the year and are usually not as cold as continental polar air masses.
 

Continental Polar

These air masses are similar to Continental Arctic, they are cold, dry, and stable. They move southward, east of the Rockies into the Plains, then eastward.
 

Maritime Tropical

Maritime tropical air masses originate over the warm waters of the tropics and Gulf of Mexico and off the Pacific coast of the southern United States, where heat and moisture are transferred to the overlying air from the waters below.
 

Continental Tropical

The source region for Continental Tropical air is the desert Southwest, the high plains and Mexico in relation to the United States.