Air Masses
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An air mass is a large body of air that has roughly the same temperature
and humidity.
When two air masses meet, the boundary between the two air masses is
called a front.
When warm air masses cool water vapor condenses to form clouds.
If temperature continues to decrease, clouds saturate and precipitation
falls from the clouds due to gravity.
Warm Fronts
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In a warm front, warm moist air mass approaches a cold air mass and slowly rises over the cold air.
The warm air mass rises because it is less dense than cold air.
When a warm front occurs nimbostratus clouds will eventually form.
Nimbostratus clouds cause grey skies form and slow, steady rain falls.
Cold Fronts
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In a cold front, cold dry air approaches a mass of warm moist air and pushes underneath it.
The warm air then rapidly rises above the cold air causing vertical cumulonimbus clouds. These clouds
contain a lot of moisture.
Since the temperature changes so quickly, the clouds release moisture in the form of thunderstorms.
The more quickly the air rises the more violent the storm becomes (hail, high winds, lightning, etc…).
However, thunderstorms pass quickly.
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Type of
Air Mass
Front
Movement
Cold Front Cold air
mass pushes
under a
warm air
mass
Barometric
Pressure
Cumulonimbus Heavy rainfall
Low
Thunderstorms
Pressure
Windy
L
Warm
Front
Warm air
mass glides
over a cold
air mass
Nimbostratus
Warm and
cold air
masses
collide and
move very
little
Cumulus and
Stratus
A cold front
overtakes a
warm front
Stratus and
cumulus
Stationary
Front
Occluded
Front
Cloud Cover
Precipitation
Slow, steady
rainfall
L
Long, off-andon rainfall
Low
Pressure
L
Steady rain
followed by
heavier rain
No Front
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Low
Pressure
Air mass(es) Cirrus
No
have similar Cumulus
precipitation
temperature
Sunny skies
and
humidity
Snow, sleet, hail, and ice are also types of precipitation
41
Low
Pressure
L
High
Pressure
H
Symbol