1. Air Masses cont.  A large body of air with the same temperature and moisture content  When air is stationary or moves slowly it takes on uniform characteristics  Classified by source region, temperature and humidity  Polar regions=cold, dry air  Tropical regions=warm, moist air

2. Types of Air Masses  Continental  Form over large landmasses  Northern Canada, southwestern USA  Low humidity  Why??  Two types Continental polar (cP): cold and dry Continental Tropical (cT): warm and dry

3. Types of Air Masses  Maritime  Form over oceans or large bodies of water  High humidity  Commonly bring rain or fog  Two types Maritime polar (mP): moist and cold Maritime tropical (mT): moist and warm

4. North American Air Masses Air MassSource LocationMovementWeather cPPolar regions in Canada South-southeastCold and dry mPPolar Pacific; polar Atlantic Southeast; southwest-south Cold and moist cTU.S. southwestNorth-northeastWarm and dry mTTropical Pacific; tropical Atlantic Northeast; north- northwest Warm and moist

6. FRONTS  When two air masses with different properties meet, density differences keep them separate.  A front is a boundary that forms between two air masses.  Four types: cold fronts, warm fronts, occluded fronts, stationary fronts

7. Cold Fronts  Forms when a cold air mass meets and pushes under a warm air mass  As warm air is lifted, cumulonimbus clouds form  Typically produces storms  Followed by cooler air

9. Warm Fronts  Forms when a warm air mass overtakes a cold air mass and moves over it.  Warm air rises over cooler air and causes slight to moderate precipitation.  Followed by warmer air

11. Occluded Front  Forms when a cold air mass quickly overtakes a warm front, and completely lifts the warm air off the ground.  Precipitation usually follows

13. Stationary Front  A front where no movement occurs.  Precipitation may occur for several days.