Warm up Warm up Poirier AIR MASSES AND

Warm up

Warm up

Poirier AIR MASSES AND FRONTS UNIT 4: WEATHER TEXT CHAPTER 17

Meteorology The study of processes that govern Earth’s atmosphere to help make weather predictions List as many things as you can think of that affect Earth’s atmosphere and the weather

Air Mass A large body of air in the lower troposphere that has uniform characteristics Similar temperature Similar humidity The interaction of air masses is what causes local weather.

North American Air Masses

What is a Weather Front? A Front is the boundary that separates opposing air masses Common in mid-latitudes (meeting place of polar and tropical air) Movement – interaction of air based on density (temperature humidity)

Cold Front Cold air mass moving in to replace warmer air More dense so moves under warmer air Pushes warmer air up (vertical flow) Brings Thunder storms in summer Less humid air Change in wind direction Short period of precipitation Moves about twice as fast as a warm front

Cold Front

Warm Front Warm air moves in and displaces cold air Less dense so rises up over the cold air Shallow slope less abrupt weather change Brings ~24 hours of increasing clouds starting with cirrus Overcast Prolonged period of precipitation After clearing warmer more humid conditions Moves about half as fast as a cold front

Warm Front

Occluded front When one cold front catches up with previous cold air mass Push warm air up Causes cloudiness and precipitation

Stationary Front When a front is no longer moving forward Warmer air rises, condenses, causes precipitation Flooding can occur

Materials hand outs Scissors Blue and red crayons Tape Turn in question sheet when finished

Review Moving Masses Answers

Passing of a low-pressure system Low pressure systems can be up to 2, 000 km across

Low pressure system Warm front, then cold front Approach of warm front, clouds increasing from cirrus to nimbostratus, steady rain Warm front passes, temp and humidity increase, winds shift, skies clear Approach of cold front, scattered showers or Tstorms Cold front passes, temp and humidity decrease, winds shift again, skies clear

Life cycle of a low-pressure system