Air Masses and Fronts

Types of Air Masses

• Maritime Tropical

• Continental Tropical

• Maritime Polar

• Continental Polar

Maritime Tropical

• Warm, humid air masses form over

tropical oceans.

• In the East these include the Gulf of

Mexico and the Atlantic Ocean.

• The masses move first into the southeast

of the United States.

• These air masses then move North and

Northeast.

Maritime Tropical

• In the West, these masses form over the

Pacific Ocean.

• Mostly effect the West Coast.

• The air masses lose moisture over the

coastal mountain ranges.

Maritime Tropical

• In summer, hot humid weather can be

found in the Eastern United States.

• Thunderstorms also are common during

this time of year.

• This usually begins in the Gulf of Mexico.

• In winter, a humid air mass can bring

heavy rain or snow.

Maritime Polar

• Cool, humid air masses form over the icy

cold North Pacific and North Atlantic

oceans.

• These air masses affect the West Coast

more than the East Coast.

• In summer, fog, rain, and cool

temperatures are found on the West

Coast.

Continental Tropical

• These air masses cover the Southwest and

northern Mexico.

• In summer these are hot dry air masses.

• Sometimes they will move northeast into

the southern Great Plains

Continental Polar

• These masses form over central and

northern Canada and Alaska.

• In winter, these air masses bring cold, dry

air to most of North America.

• In summer, the air mass is milder.

• Storms occur when CPM’s moving south

collide with MTM’s moving north.

How Air Masses Move

• Prevailing Westerlies

• Jet Streams

• Fronts

Prevailing Westerlies

• These air masses move from west to east.

• Example: Maritime polar air masses from

Pacific Ocean are blown onto West Coast.

• Low clouds and showers would come out

of this system.

Jet Streams

• Remember that these high speed winds

are over 10 km high.

• These winds travel west to east.

Fronts

• When you have different air masses

meeting each other, the boundary is

called a front.

Types of Fronts

• Cold Front

• Warm Front

• Stationary Front

• Occluded Front

Cold Front

• A cold front overtakes a warm front very

quickly.

• The warm air rises and expands.

• If there is a lot of water vapor then you

would have heavy rain, thunderstorms, or

heavy snow.

Cold Front

• If warm air has less water vapor, then

you’ll have cloudy skies.

• When the weather clears the cold front

brings in cold dry air and low

temperatures.

Warm Fronts

• A warm air mass over takes a cold slow

moving air mass.

• If the warm air is humid then you’ll have

light rain or snow falls along the front.

• If the warm air is dry then you’ll get

scattered clouds.

Warm Fronts

• Warm air fronts still move slowly and the

weather may be rainy for several days.

• When a warm humid front passes you get

humid warm weather.

Stationary Fronts

• Sometimes you get a standoff between two

fronts.

• You get the potential for fog, rain, or snow

for extended period of time.

Occluded Fronts

• This front happens when a warm air mass

is caught between two cold fronts.

• The two cold air masses push the warm

air mass up.

• The temperature becomes cooler on the

ground.

Occluded Fronts

• The warm air mass has been cut off or

occluded from the ground.

• Warm air cools and its water vapor

condenses.

• Weather could become cloudy with either

rain or snow.

Cyclones and Anticyclones

• Sometimes air masses colliding will

become distorted through either

mountains or high winds.

• This causes bends along the front.

• Air begins to swirl, causing a low front.

• The warm air at the center of cyclone

rises and the air pressure decreases.

Cyclones and Anticyclones

• A swirling center of low pressure is called

a cyclone.

• This is the Greek word for “wheel”.

• Winds turn counter clockwise in the

Northern Hemisphere and the opposite in

the Southern Hemisphere.

Cyclones and Anticyclones

• Cyclones and decreasing air pressure are

associated with clouds, wind, and

precipitation.

Cyclones and Anticyclones

• An Anticyclone is a high pressure system

of dry air.

• Winds spiral outward from the center of

an anticyclone.

• Winds move clockwise in the Northern

Hemisphere.

Cyclones and Anticyclones

• Cool air moves down from the

troposphere.

• The cool air falls, it warms up, and

relative humidity drops.

• The weather with this system is usually

dry and clear.