
Air mass
-Large body of air where temperature and moisture are similar
throughout the mass
-changes in weather are caused by movement and interaction
of air masses

Characteristics of air masses
1- moisture
2-temperature
Source region – an area over which an air mass forms
Source regions are identified by 2 letters
EX: Maritime polar
mP
1st letter represents moisture level
2nd letter represents temperature

Cold Source regions (3) that affect weather
in the continental US
1
Continental Polar (cP)
Forms over N Canada
Winter-brings extremely cold air to U.S.
Summer-brings cool dry air to U.S.
2
Maritime Polar (mP)
water (wet) & cold
Forms over N Atlantic Ocean
Winter- brings rain and snow to Pacific coast area (CA)
Summer-brings cool, frosty air to Pacific Coast area
3
Maritime Polar (mP)
Forms over N Pacific Ocean
Winter-cool and cloudy to N England area (MA)
summer-cool and foggy to N England area

WARM Source Regions(4) that affect weather
in the continental US
1
Maritime Tropical (mT) wet and warm
Source region- warm areas of the Pacific Ocean
Summer: brings hot, humid weather with hurricanes and
thunderstorms to the West coast and Midwest
2
Maritime Tropical (mT) wet and warm
Source region- warms areas of the Atlantic Ocean
Summer: brings hot, humid weather with hurricanes and
thunderstorms to the East coast and Midwest
3
Maritime Tropical (mT) wet and warm
Source region-over Gulf of Mexico
Weather to the East coast and Midwest:
Summer: hot, humid weather with hurricanes and thunderstorms
Winter: mild, often cloudy
4
Continental Tropical (cT) dry and warm
Source region: deserts of N Mexico and SW U.S.
Summers are clear, dry and hot

Fronts are where two types of air masses meet

Four kinds of fronts
1-cold fronts- cold air mass moves under warm air mass
thunderstorms, heavy rain or snow
2-warm fronts-warm air mass moves over cold air mass
drizzly rain followed by clear and warm weather
3-occluded fronts-warm air mass gets caught b/t 2 cold air masses
cool temps and large amounts of rain and snow
4-stationary fronts-cold air mass meets a warm air mass
brings many days of cloudy, wet weather

Cyclones are areas with lower pressure than the areas around them
-air masses converge and rise
-rising air from the center of a cyclone cools and forms clouds
causing stormy weather
Anticyclones are areas with higher pressure than the areas around them
-air masses diverge and sink
-sinking air of an anticyclone gets warmer and absorbs moisture
bringing dry, clear weather