Introduction to Air Masses and Weather Fronts
Air Masses
An air mass is a large body of air that has relatively uniform temperature and humidity characteristics.
The regions where air masses form are referred to as air mass source regions. If air remains over a
source region long enough, it will acquire the properties of the surface below. Ideal source regions
are regions that are generally flat and of uniform composition. Examples include central Canada,
Siberia, the northern and southern oceans and large deserts.
Air Mass Classification
Air masses are classified according to their temperature and moisture characteristics. They are
grouped into four categories bases on their source region. Air masses that originate in the cold, polar
regions are designated with a capital “P” for polar. Air masses that originate in the warm tropical
regions are designated with a capital “T” for tropical. Air masses that originate over land will be dry
and are designated with a lowercase “c” for continental. Air masses that originate over water will be
moist and are designated with lowercase “m” for maritime. These letters are combined to indicate the
type of air mass:
cP: cold, dry air mass ~ mP: cold, moist air mass
cT: warm, dry air mass ~ mT: warm, moist air mass
In winter, one more type of air mass may form, an extremely cold, dry air mass referred to as cA,
continental arctic. Once formed, air masses can move out of their source regions bringing cold,
warm, wet or dry conditions to other parts of the world.
