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Weather Fronts
Air Masses
• Global winds result from
large amounts of air
moving from high
pressure to low.
• A large, homogenous
parcel of air is called an
air mass.
• These huge masses of air
can cover 100 million
hectares from the ground
to the tropopause.
Types of Air Masses
• Air masses are named for two properties of the air in the
mass—its temperature and water content.
• Dry air masses begin over land masses (continents) and
are called continental.
• Wet air masses start over oceans and are called
maritime (from Latin “of the sea”).
• Cold air masses form near the north and south poles, so
we call them polar.
• Warm air masses come from the tropics and are called
tropical.
• The four types of air mass are continental polar,
continental tropical, maritime polar, and maritime
tropical.
Fronts
• The place where two
air masses come
together is called a
front, because it is
often the first part we
see of a storm.
• A storm front can be
dangerous, bringing
strong wind, heavy
rain, lightning, or
tornadoes.
Types of Fronts
• Fronts are
divided into
types based
on how the air
masses are
moving.
• Each type of
front has
different line
to show it on
a weather
map.
Cold Fronts
• When a polar air mass is
moving toward a tropical
mass, we call it a cold
front.
• Cold fronts are
represented by a blue line
with triangles showing
which way the front is
moving.
• Cold fronts push warm air
up as they pass causing
clouds and storms to form
ahead of a cold front.
Warm Fronts
• When a tropical air mass
runs into a polar one, we
call it a warm front.
• Warm fronts are shown
with a red line and
semicircles to show the
direction of movement.
• The warm air is forced up
and over the cold air
often forming clouds
ahead of the front.
Stationary Fronts
• When polar and tropical
air masses pass by each
other in opposite
directions, we call it a
stationary front.
• A stationary front is
shown by alternating blue
triangles and red
semicircles.
• The weather tends to be
milder than with warm or
cold fronts, but since the
rain is likely to continue
for hours or days it can
cause flooding.
Occluded Fronts
• When a tropical mass
gets caught between two
polar masses, we call it
an occluded front.
• Occluded fronts are
shown by alternating
triangles and semicircles
in blue or purple.
• The warm mass is forced
up and over the slower
moving cold mass,
created cold rains or in
winter snow or freezing
rain.