air masses and fronts · fronts •when you have different air masses meeting each other, the...
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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.