Air Masses and Fronts - rbgusd.k12.ca.usMaritime Tropical •Warm, humid air masses form over tropical oceans. •In the East these include the Gulf of Mexico and the Atlantic Ocean.

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.