Air Masses and Fronts

1. Air Masses and Fronts Pgs. 44 - 47

2. Air Masses • An air mass is a large body of air that has similar temperature and moisture throughout. • An air mass gets its moisture and temperature characteristics from the area over which it forms, called source regions. • Each air mass is represented with a symbol that represents its temperature and characteristics. • There are four types we will discuss.

3. Cold Air Masses • Most of the cold winter weather in the U.S. is influenced by polar air masses. • Continental Polar (cP) air mass develops over land in northern Canada. • The air is dry and cool. • Maritime Polar (mP) air mass develops over the Northern Pacific and Northern Atlantic Oceans. • The air is moist and cool. • It brings snow, rain, and cloudy conditions.

4. Warm Air Masses • Several warm air masses influence the weather in the U.S. called tropical air masses. • Maritime Tropical (mT) air masses form over warm areas in the Pacific Ocean and Gulf of Mexico. • They bring warm, humid air and sometimes thunderstorms. • Continental Tropical (cT) air masses form over the deserts of northern Mexico and the southwestern U.S. • It brings hot, dry air and clear skies.

5. Fronts • When two different air masses meet a boundary between them forms, called a front. • Weather at a front is usually cloudy and stormy. • The only place where fronts do not occur are at the tropics, because only warm air exists in that area.

6. Cold Front • A cold air mass meets and displaces a warm air mass because it is more dense and pushes the warm air up. • They produce thunderstorms, heavy rain or snow. • Cold weather usually follows a cold front.

7. Warm Front • A warm air mass meets and overrides a cold air mass. • The warm, less dense air moves over the cold air and gradually replaces it. • Warm fronts bring drizzly precipitation • After a warm front, weather is warm and clear.

8. Occluded Front • A faster moving cold air mass overtakes a slower-moving warm air mass and forces the warm air up. • The cold air mass continues until it meets a cold air mass that is warmer. • Occluded fronts have cool temperatures and large amounts of precipitation.

9. Stationary Front • A cold air mass meets a warm air mass and little horizontal movement occurs. • A stationary front produces some drizzly precipitation and some warm clear conditions afterwards.