1. Air Masses and Fronts

2. Types of air masses An air mass is a huge body of air that has similar temperature, humidity and air pressure throughout it. There are four major types of air masses that influence the weather in North America: maritime tropical, continental tropical, maritime polar and continental polar.

3. Maritime Tropical Air Mass Warm humid air masses that form over oceans near the tropics. In the summer, maritime tropical air masses bring hot, humid weather. In the winter, maritime tropical air masses bring heavy rain or snow.

4. Maritime Polar Air Masses Cool humid air masses form over the icy cold North Pacific and North Atlantic oceans. These masses of cool humid air bring fog, rain and cool temperatures to the West Coast.

5. Continental Tropical Hot dry air masses form only in the summer over dry areas of the Southwest and Northern Mexico.

6. Continental Polar Air Masses Form over central and northern Canada and Alaska. Continental polar air masses bring cold or cool air. In winter, continental polar air masses bring clear, cold, dry air to North America.

7. How Air Masses Move Air masses move because of the major wind belts pushing them along.

8. Do Now: What is a front?

9. Fronts As huge masses of air move across the land and the oceans, they bump into each other but they do not mix. Where the two air masses meet and do not mix is called a front. You will find storms and changeable weather at fronts

10. Types of fronts There are four types of fronts: cold fronts, warm fronts, stationary fronts and occluded fronts. The kind of front that develops depends on the characteristics of the air masses and how they are moving.

11. Cold Front A cold front forms when fast moving cold air mass runs into a slowly moving warm air mass. The cold air mass forces the warm air mass up causing clouds, rain or snow. Cold fronts are also known for thunderstorms.

12. Warm Front Warm air mass collides with cold air mass causing the less dense warm air to rise. If the warm air is humid, this collision causes clouds and rain. If the warm air is dry, this collision causes scattered clouds.

13. Stationary Front Cold and warm front meet but neither are able to push the other out of the way. At the front, clouds, fog and rain develops. If a stationary front remains stalled over an area, it may bring many days of clouds and precipitation.

14. Occluded Front In an occluded front, a warm air mass is caught between two cooler air masses. The warm air is forced up as the denser cool air pushes into the area. The weather gets cooler and can cause clouds and precipitation.