Air Masses Air masses are large bodies of

Air Masses • Air masses are large bodies of air where temperature and moisture content are constant throughout. • Moisture content and temperature of a mass are determined by the area over which the air mass forms. • These areas are called source regions.

Air Masses that Affect weather in North America

Cold Air Masses – Continental polar (c. P) forms over northern Canada; brings extremely cold weather during winter; brings cool dry weather during summer – Maritime polar (m. P) forms over North Pacific Ocean; cool, very wet; rain and snow during winter; foggy during summer

Warm Air Masses • There are three warm air masses that affect the U. S. – Maritime tropical (m. T) forms over warm water in the Pacific Ocean – Maritime tropical (m. T) forms over the Gulf of Mexico and the Atlantic Ocean; brings hot, humid weather and hurricanes and thunderstorms during the summer; In winter, brings mild, cloudy weather – Continental Tropical (c. T) forms deserts of Mexico and Southwestern U. S. ; brings clear, hot, dry weather during summer

Fronts • The boundary between air masses of different densities and different temperatures are called Fronts • There are four different fronts that you need to know : Cold, warm, occluded, and stationary

Cold Front • Cold Front – cold air moves under warm air • Cold fronts can move quickly and bring thunderstorms, heavy rain, or snow • Cooler weather usually follows a cold front because the air mass behind the cold front is cooler and drier than the air mass replacing it

Warm Front • Warm Front – warm air moves over cold air • In a warm front, the warm air gradually replaces the cold air • Warm fronts generally brings drizzly rain followed by clear and warm weather.

Occluded Front • Occluded Front – warm air mass is caught between two colder air masses. Brings cool temperature and large amounts of rain and snow.

Stationary Front • Stationary Front – cold air mass meets warm air mass; remain separate; not enough energy to move warm air above cold air mass; can bring many days of cloudy, wet weather.

Front Illustrations • Front Illustrations

Air Pressure and Weather • Cyclones – areas in the atmosphere that has lower pressure – Air masses come together ( converge) and rise – Spiral – Causes Stormy weather • Anticyclones – Areas that have high pressure – Air masses move apart ( diverge) – Sinking air denser then surrounding air and pressure is higher – Brings dry, clear weather.

Cyclone and Anticylone

Quick Check Air that has similar characteristics and covers a large region is called a. a cloud b. a(n) air mass c. a storm d. weather

Quick Check Continental Polar air masses form over a. Canada b. the Caribbean Sea c. the gulf of Mexico

Quick Check Maritime Polar masses form over a. Canada b. the Gulf of Mexico c. the North Atlantic Ocean

Quick Check Maritime Tropical air masses form over a. Canada b. the North Pacific Ocean c. the ocean near the equator

Quick Check Air masses usually move _____ across the United States. a. east b. west c. southwest d. northwest

Quick Check A front forms a. inside an air mass. b. on the surface of an air mass. c. around an air mass. d. between two air masses.

Quick Check A cold air mass forces a warm air mass to move a. b. c. d. downward. upward. to the side. to the back.