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Weather Concepts
Air Masses
Air masses are large bodies of air that
have the same temperature and humidity
throughout
 They can form over land or water
 They can range from 100 km to 1000 km
in size

Air Masses
A warm air mass consists of warm air and
it can be dry or humid
 If the air mass forms over warmer oceans
then the air mass will be humid (maritime
tropic)
 If the air mass forms over land then the air
mass will be dry (continental tropic)

Air Masses
A cold air mass consists of cold air and it
can be dry or humid
 If the cold air mass forms over cold ocean
water then it will be humid (maritime
polar)
 If the cold air mass forms over cold land
then it will be dry (continental polar)
 Any air mass that forms over the Arctic is
very cold and very dry

Fronts
Cold air masses from the north and warm
air masses from the equator move towards
each other
 When these mass collide they create
fronts
 The difference in temperatures found
between the air masses creates a
boundary

Fronts

Warm front occurs when a warm air
mass comes into an area and pushes the
colder air up and out. This front brings
periods of light rain.

Cold front occurs when a cold air mass
comes into an area and pushes a warm air
mass up quickly. This front usually brings
thunderstorms or very heavy rain.
Fronts
Occluded front occurs when a fast
moving cold air mass collides with a warm
front and forces it upwards.
 As a result the cold air mass catches up to
the other cold air mass on the other side of
the front.
 This type of front can sometimes bring
thunderstorms but usually results in drying
of the air mass

Fronts
Stationary front occurs when a a cold air
mass meets a warm air mass but does not
move.
 This type of front brings cloudy skies and
precipitation (usually lighter rain) for longer
periods of time

Types of Fronts

http://www.phschool.com/atschool/phsciex
p/active_art/weather_fronts/
Pressure Systems
A low pressure system forms as a warm
air mass travels over warm land or oceans
 The air flows up and away from
earth’s surface which lowers
the pressure on the earths surface
 Water vapor condenses and
precipitation can be expected

Pressure Systems
A high pressure system forms over a cool
ocean or land and can be very large
 The dense air falls towards the earth’s surface
causing the air pressure to increase
 As the high pressure air falls to earth
it becomes warmer and drier
 It normally brings sunny and
clear skies
