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Unit 7: Weather Systems
Air Masses & Fronts
Air Mass: a large portion (500-1500 mi) of the
troposphere that stagnates (stays) over part of the
Earth’s surface and acquires the characteristics of that
surface.
1. Has generally uniform temp and humidity
throughout
2. Source Area: surface over which an air mass
stagnates
Air masses are named based on the temperature and
humidity of their source region. See ESRT page
___ for a list of air mass names and symbols.
Complete the table below.
Word/symbol bank:
cP
Mexico
Humid
Warm
mP
Gulf of Mexico
Dry
Canada
cA
North Atlantic
Super-mad-cold
mT
South Atlantic
Cold
cT
South Pacific
North Pacific
Source TEMPERATURE HUMIDITY Enters U.S. from…
Region
cP
cA
Super-mad-cold
cT
Dry
South Pacific, Gulf of Mexico
mP
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Unit 7: Weather Systems
Air Masses & Fronts
Fronts: interfaces between air masses with different
characteristics.
1. Cold Front- the leading edge of an advancing
cold air mass.
Cold Front Cross-section
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2.
warm air ahead of front is lifted up
and over (less dense)
tall, puffy clouds
can get intense showers/thunderstorms
at frontal boundary
Cirrus clouds are blown ahead of the
front by upper level winds
further behind the front, the air is
quite dry, few clouds
steep frontal boundary, slopes backward into the cold air
frontal speed averages 15-25 knots
Warm Front: leading edge of a warm air mass
Warm Front Cross-section
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layered clouds (Stratus)
frontal surface has a much smaller
slope than for cold fronts
often produces wide-spread
nimbostratus (precip) AHEAD of front
warm air climbs up over the receding
cold air mass
frontal speed averages 5 – 15 kts
high cirrus clouds appear a day before
the front arrives
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Unit 7: Weather Systems
Air Masses & Fronts
Occluded Front: A faster cold front overtakes a
warm air mass
Occluded Fronts (Occlusion)
 Massive adiabatic cooling and
condensation
 Causes heavy precipitation in
the occluded area
 Portion of warm air mass lifted
off the ground
Stationary Fronts
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has little/no movement
denoted by alternating cold/warm frontal symbols
Associated weather:
o clear, partly cloudy, cloudy, light precip
o usually nothing severe
If the stationary front starts moving NORTHEAST in the example to the right it
will become a ___________________ front.
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