Air Masses and Fronts

Warm Up: What type of rock is formed from cooling lava?

Air Mass VIDEO Clip

Air Masses• Air masses have the same properties as the surface

over which it develops:

Maritime = WetContinental = DryPolar = ColdTropical = Warm

mP = wet/cold

cP = dry/cold

mT = wet/warm

cT = dry/warm

Air Masses in North America

Fronts

• A front is the boundary where two air masses meet.

• Types of fronts:1. Warm Front

2. Cold Front

3. Occluded Front

4. Stationary Front

WARM AIR

COLD AIR

FRONT

Front VIDEO Clip

Cold Front• Cold dense air

pushes under a warm air mass.

• The cold dense air moves faster and causes the warm air rises quickly.

• Narrow bands of violent storms form.

Why do cold fronts bring heavy rain and storms?

• Cold air interacting with warm air = a sudden drop in temperature = CONDENSATION occurs quickly and a fast difference in pressure

• Creates cumulonimbus clouds• Cold dense fast moving air = high winds

What you see in a weather map!

Cold Front Video Clip

Warm Front

• Warm air slides over departing cold air.

• Large bands of precipitation form

Why do warm fronts bring mild weather?

• It’s more difficult for the warm air to move against the cold dense air so there is a gradual difference in pressure and temperature

What you see in a weather map!

Warm Front Video Clip

Occluded Front• Two cold air masses merge and force

warm air between them to rise quickly.

• Strong winds and heavy precipitation will occur.

Why do occluded fronts bring heavy rain and storms?

• Cold air that is more dense moves into an area of low pressure = CONDENSATION occurs quickly

• Forms cumulonimbus and nimbostratus clouds

What you see in a weather map!

Stationary Front

• Warm and/or cold front stops moving.

• Light wind and precipitation may occur across the front boundary.

Why do stationary fronts bring long light precipitation?

• Neither front is strong enough to move the other

• Can stay put for days• Differences in temperature = rain or snow

What you see in a weather map!

Cyclones and Anticyclones• Areas of HIGH and LOW pressure• Cyclone = LOW PRESSURE = spin

counterclockwise = associated with storms and precipitation

• Anticyclone = HIGH PRESSURE = spin clockwise = associated with fair weather.

Cyclones and Anticyclones in the USA

Cyclone Video Clip