1. Air Masses and Fronts Mr. Bombick 7 th Grade Science

2. Types of Air Masses There are four major types of air masses that affect our weather. These four major types of air masses are maritime tropical, continental tropical, maritime polar, and continental polar. Tropical air masses are warm while polar air masses are cold. Maritime air masses form over oceans and continental air masses form over land.

3. Types of Air Masses (cont.) Maritime tropical air masses bring warm and humid air first to Southeastern and Southwestern parts of the US. In summer, rain and thunderstorms can result and in winter, heavy rain or snow may result. Maritime polar air masses bring cold and humid air mainly to the West Coast. They may result in fog and rain in summer and snow in the winter.

4. Type of Air Masses (cont.) Continental tropical air masses form over dry areas of the Southwest and northern Mexico. These air masses may bring hot and dry conditions to the lower Southern plains. Continental polar air masses form over central and northern Canada and Alaska. These air masses can bring clear, cold, and dry air to much of the US in the winter. During the summer, these air masses bring colder air to the US and storms may occur if this air mass collides with a maritime tropical air mass.

5. How Air Masses Move Prevailing westerlies (major wind belt over the continental US) push air masses from west to east. Jet streams help direct air masses from west to east. Fronts are the boundaries of where large air masses meet or collide. Fronts are often areas of changing weather.

6. Warm air rises Cold air sinks Warm air can contain more water than cold air

7. Types of Fronts Cold fronts develop when a fast-moving cold air mass overtakes a warm air mass. There is usually significant cloud formation and heavy rain or snow may fall if the warm air contains a lot of water vapor. Sudden weather changes are possible including thunderstorms. After a cold front passes, colder and drier air moves in, often with clear skies.

8. Types of Fronts (cont.) Warm fronts result when a fast-moving warm air mass overtakes a slower moving cold air mass. Light rain or snow may fall along the front which may remain for several days. After a warm front passes, the weather may be warmer and more humid.

9. Types of Fronts (cont.) A stationary front is where a warm and cold front meet but, neither can move the other. There can be precipitation and cloud formation at the boundary between the two fronts. A stationary front can stall which may result in many days of clouds and precipitation.

10. Types of Fronts (cont.) An occluded front is a complex weather pattern where a warm front becomes trapped between two cold fronts. There may be precipitation associated with this front if the warm air starts to cool and water vapor condenses.