Air Masses
Introduction:
An air mass is a large body of air with similar temperature and moisture properties throughout. The
best source regions for air masses are large flat areas where air can be stagnant long enough to take
on the characteristics of the surface below. As an air mass moves away from its source region, it is
modified as it encounters conditions different than those found in the source region. Air masses
typically clash in the middle latitudes, producing some very interesting weather.
The purpose of this activity is to introduce air masses that commonly influence the weather in the
United States, characteristics of these air masses, and how to identify air masses on weather maps.
Continental Polar Air Masses
cold temperatures and little moisture
Those who live in northern portions of the United States expect cold weather during the winter
months. These conditions usually result from the invasion of cold arctic air masses that originate
from the snow covered regions of northern Canada. Because of the long winter nights and strong
radiational cooling found in these regions, the overlying air becomes very cold and very stable. The
longer this process continues, the colder the developing air mass becomes, until changing weather
patterns transport the arctic air mass southward.
Maritime Tropical Air Masses
warm temperatures and rich in moisture
Maritime tropical air masses originate over the warm waters of the tropics and Gulf of Mexico,
where heat and moisture are transferred to the overlying air from the waters below. The northward
movement of tropical air masses transports warm moist air into the United States, increasing the
potential for precipitation.
Air Mass #1
Type of Air Mass:
Source Region:
Relative Temperature:
Wind Direction:
Moisture Content:
Air Mass #2
Find the Air Masses:
2) One way of identifying a tropical air mass on the weather map below is to look for a region of
higher temperatures. To find a polar air mass, look for a region of colder temperatures. The image
below is a map of surface observations and for this part of the activity, use the temperature field
to draw two lines; a red line to outline the edge of a tropical air mass and a blue line to identify a
Find the Air Masses:
2) One way of identifying a tropical air mass on the weather map below is to look for a region of
higher temperatures. To find a polar air mass, look for a region of colder temperatures. The image
below is a map of surface observations and for this part of the activity, use the temperature field
to draw two lines; a red line to outline the edge of a tropical air mass and a blue line to identify a
polar air mass.
Temperature:
The value highlighted in yellow located in the upper left corner is the temperature in degrees Fahrenheit. In
this example, the reported temperature is 64 degrees.