Air Massesrain_anim.giflightning_and_cloud_anim.gif
by Manuel Rodriguez
An air mass is a large body of air with the same pressure, temperature and humidity.
How Air Masses are Described
  • Tropical is warm air masses form in the tropics and have low air pressure.
  • Polar, or cold, air masses have high air pressure.
  • Maritime air masses form over oceans. The water evaporates from the oceans so the air can become very humid.
  • Continental air masses form over land in the middle of continents, and are dry.

The four types of air mass that influences the weather in the United States
1. Continental Polar
2. Continental Tropical
3. Maritime Topical
4. Maritime Tropical

Continental Polar air mass usually is created from the invasion of cold arctic air masses that starts from the snow covered regions of northern Canada. Because of the long winter nights and strong 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.

Continental Tropical air masses cover a smaller area than other air masses. They usually move northeast, bringing hot, dry weather to the southern Great Plains. However, southerly winds ahead of migrating cyclones occasionally transport a tropical air mass northward during the winter season.
Maritime tropical air masses starts over warm waters of the tropics and Gulf of Mexico, where heat and moisture are transferred to the 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.

Maritime Polar is cool, humid air masses which are formed over icy cold North Pacific and North Altantic oceans. This air mass affects the West Coast more than it affects the East Coast. During the summer. this air mass brings cool, humid, air which brings fog, rain, and cool temperatures to the West Coast.