Air Masses and Fronts

1. Air Masses and Fronts

2. What are the four types of air masses? • Maritime Tropical • Maritime Polar • Continental Tropical • Continental Polar

3. Maritime Tropical • Warm humid air masses from oceans near the tropics. • They form over the Gulf of Mexico and the Atlantic Ocean. • In the summer time maritime tropical usually bring hot humid weather. • In winter, a humid air mass can bring heavy rain or snow.

4. Maritime Polar • Cool humid air masses form over the icy cold North Pacific and North Atlantic oceans. • The air masses affect the west coast more than the east coast. • In the summer they often bring rain, fog, and cool temperatures to the west coast.

5. Continental Tropical • Hot dry air masses form only in the summer over dry areas of southwestern and northern Mexico. • Cover a smaller area than other air masses. • Bring hot, dry weather to the south.

6. Continental Polar • Form over central and northern Canada and Alaska. • Bring cool and cold air. • In winter they bring clear, cool, and dry air to most of northern America. • In the summer, storms may occur when continental air masses move south and meet maritime tropical that move north.

7. How do air masses move? • The prevailing westerlies are the major wind belts in the United States. • Prevailing westerlies push air masses from west to east.

8. Fronts • When air masses meet is a front, the collision often causes storms and weather changes. • A front may be 15 to 200 kilometers wide and extend as much as 10 kilometers up to the troposphere. • The kind of front that develops depends on the characteristics of the air masses and how they move.

9. There are four types of fronts. • Cold Fronts. • Warm Fronts. • Stationary Fronts. • Occluded Fronts.

10. Cold Fronts • Cold air is dense and tends to sink. • Warm air is less dense and tends to rise. • When a moving cold air mass runs into a slowly moving warm air mass, the denser cold air slides under the warmer air. • Warm air can hold more water vapor than cool air. • If there is a lot of water vapor in the warm air heavy rain or snow may fall. • Cold fronts move quickly so they can cause weather changes. • After a cold front passes, cool, dry air moves in.

11. Warm Fronts • A moving warm air mass collides with a slowly moving cold air mass. • If the warm air is humid showers and light rain might. fall along the front where the warm and cold air meet. • If the warm air is dry scattered clouds may form. • After a warm front passes through an area the weather is likely to be warm and humid. • Winter warm fronts bring snow.

12. Stationary Fronts • Sometimes cold and warm air masses meet but neither one has enough force to move. • Where the warm and cold air meet, water vapor in the warm air turns into rain, snow, fog, or clouds.

13. Occluded Fronts • A warm air mass is caught between two cooler air masses. • As warm air cools and its water vapor condenses, the weather may turn cloudy, rainy, or snowy.

14. Cyclones and Anticyclones • As warm air at the center of a cyclone rises , the air pressure decreases. • Winds in s cyclone spin counterclockwise in the Northern Hemisphere. • As air rises in a cyclone the air cools forming clouds and precipitation. • Winds spiral outward from the center of an anticyclone, moving towards areas of low pressure. • Winds in an anticyclone spin clockwise in the Northern Hemisphere.

15. Cyclones • Hurricanes are very large cyclones that can cause widespread damage.

16. Anticyclones • Air flows clockwise around a high-pressure system in the northern hemisphere. • Air tends to sink near high-pressure centers, which inhibits precipitation and cloud formation.

17. Vocabulary • Air mass- a huge body of air that has similar temperature, humidity, and pressure. • Tropical- or warm air masses form in the tropics and have low air pressure • Polar- or cold air masses from North of 50o N latitude and South of 50o S latitude. • Maritime- air masses that form over oceans • Continental- air masses form over land in the middle of continents and are dry. • Front- the area where the masses meet and do not mix. • Occluded- the warm air masses is cut off. • Cyclone- a swirling center of low air pressure. • Anticyclone- area of high pressure centers of dry air.

18. Section 1 Review 1.) What two main characteristics are used to classify air masses? • Temperature • Humidity

19. Section 1 Review 2.) What's a front? Name and describe the four fronts. • Front- the area where the masses meet but do not mix. • Cold Fronts- when a rapidly moving cold air mass runs into a slowly moving air mass, the denser cold air slides under the lighter warm air. • Warm Fronts- a moving warm air mass collides with a slowly moving cold air mass. • Stationary Fronts- sometimes cold and warm air masses meet but neither one has enough force to move. • Occluded Fronts- a warm air mass is caught between two cooler air masses.

20. Section 1 Review 3.)What is a cyclone? What kind of weather does it bring? • Cyclone- a swirling center of low air pressure. • A cyclone usually brings precipitation and usually forms clouds.

21. Section 1 Review 4.) Why do maritime polar air masses have more affect on the west coast than the east coast? • Maritime polar air masses has more affect on the west coast than the east coast because, of the cool humid air.