1. Air Masses

2. Air Mass Descriptors: Continental: Originates over land- Dry Continental: Originates over land- Dry Maritime: Originates over ocean -Moist Maritime: Originates over ocean -Moist Polar: Originates from near the poles- Cold Polar: Originates from near the poles- Cold Arctic: Originates near the Arctic circle- Cold Arctic: Originates near the Arctic circle- Cold Tropical: Originates near the Equator- Warm Tropical: Originates near the Equator- Warm

3. Definition: Air mass - a large dome of air which has similar horizontal temperature and moisture characteristics throughout. Air mass - a large dome of air which has similar horizontal temperature and moisture characteristics throughout. Very similar to a balloon. Very similar to a balloon.

4. Continental Arctic (cA): Frigid (cold)– record low temperaturesFrigid (cold)– record low temperatures Dry - very low dew pointsDry - very low dew points Dense - very high barometric pressureDense - very high barometric pressure Usually originate north of the Arctic CircleUsually originate north of the Arctic Circle  Siberian Express Usually once or twice a winterUsually once or twice a winter very rarely form during the summervery rarely form during the summer  because the sun warms the Arctic.

5. Continental polar (cP): Cold and dry - stableCold and dry - stable Usually originates in NW CanadaUsually originates in NW Canada Influences mainly the northern USAInfluences mainly the northern USA Responsible for clear and pleasant weather during the summerResponsible for clear and pleasant weather during the summer Usually in winterUsually in winter Creates troughs in the polar jet streamCreates troughs in the polar jet stream Lake effect snow in Great Lakes areasLake effect snow in Great Lakes areas

6. Maritime polar (mP): Cool and moist - unstableCool and moist - unstable Originate over N. Atlantic and N. PacificOriginate over N. Atlantic and N. Pacific Main Influence - the Pacific Northwest and the Northeast.Main Influence - the Pacific Northwest and the Northeast. can form any time of the yearcan form any time of the year Generally not as cold as cP air massesGenerally not as cold as cP air masses

7. Maritime tropical (mT): Warm and very moist – unstableWarm and very moist – unstable Originate in the Gulf of Mexico and the Southern Atlantic OceanOriginate in the Gulf of Mexico and the Southern Atlantic Ocean Influences the eastern USAInfluences the eastern USA Most prevalent during summerMost prevalent during summer Responsible for hot, humid summer days across the South and the East.Responsible for hot, humid summer days across the South and the East.

8. Continental Tropical (cT): Very Hot and very dry – stable aloftVery Hot and very dry – stable aloft Originates in Desert Southwest and northern MexicoOriginates in Desert Southwest and northern Mexico Occurs in the summer, rarely in winterOccurs in the summer, rarely in winter Usually keeps the Desert Southwest scorching above 100 o F during summerUsually keeps the Desert Southwest scorching above 100 o F during summer Generally clear skies, hot, low humidityGenerally clear skies, hot, low humidity

9. Source Regions