This lecture discusses different weather types based on air mass characteristics. Air masses are large bodies of air that have similar air and dew point temperatures. They usually form over flat areas with similar surfaces and light winds.
That allows the air masses to take on the characteristics of the surface. Air masses are usually about as large as a region or smaller. like the size of the southeastern United States. Air masses are classified based on moisture and thermal characteristics.
Maritime air masses form over water and contain high dew point temperatures. Air masses with low dew point temperatures are continental, forming over land. Air temperatures that are warmer come from the tropics.
So, warmer air masses are tropical. As temperatures decrease, they're labeled polar or arctic if they're very cold. When we talk about air masses, we use a contraction that identifies the moisture content and air temperature.
Moisture is listed first, then air temperature. For example, an MT air mass is maritime tropical, with high dew points and high air temperatures. A CP air mass is cold and dry. The CP air mass that's cold and dry with low air temperatures and low dew point temperatures usually forms near the Canadian plains in North America. It plunges south on the lee side of the Rockies and sometimes creates upslope precipitation.
As the CP air mass moves over the Great Lakes in the winter, it forms lake effect snow. Cold dry air moving over a warm body of water, the water evaporates and reaches saturation. The lake effect snow belt is on the lee side of the lakes. During the summer, the CP air mass can help cool hot, humid conditions.
The MP air mass is cool and moist with cool air temperatures and dew points that are close to saturation. It's often a modified CP air mass that came from Siberia. As that air mass moved across the North Pacific, it picked up moisture.
As the MP air mass approaches the west coast of North America, it hits the Olympic Mountains and the Cascades. This creates orographic precipitation. on the windward side of the mountains.
The MT air mass is warm and moist, with high air temperatures and high dew point temperatures. It moves into the southeastern United States from the Gulf of Mexico. An air mass with high dew point temperatures is usually slightly unstable, so the MT air mass can generate a lot of thunderstorms. The MT air mass is responsible for thunderstorms during the Arizona monsoon.
The CT air mass is warm and dry. It usually forms in the Four Corners region and West Texas in the summer. It has high air temperatures and low dew point temperatures.
When the CT pushes next to the MT air mass, the boundary is a dry line. The dry air is pushed over the moist air and that creates a vapor gradient. That gradient acts as a lifting mechanism where storms can usually form later in the afternoon.