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Chapter 16
Air Masses and Fronts
Air forms in large
clumps and move
over the Earth’s
surface and slowly
change. These huge
bodies of air that
cover thousands of
kilometers are called
AIR MASSES.
An air mass has some of the same general
properties as the land or water that it forms
over.
Two Properties of air masses are:
1. Moisture content
2. Temperature
Air Masses
•A huge section of air
from the lower
troposphere that has
the same kind of
weather throughout
Air Mass
• A large body of air where temperature and
moisture content are constant throughout.
• Illustrate a picture to represent this
statement/definition.
Types of air masses
•mT
–Maritime
Tropical
Warm Moist
Air usually
over tropical
waters
Maritime Tropical
• Air mass brings warm humid air from the
south Pacific ocean to California and
Southwest.
• Air mass brings warm humid air from the
Gulf of Mexico and south Atlantic Ocean.
•mP
–Maritime
Polar
Cold Humid
air coming
from over
cold ocean
waters
Maritime Polar
• From Pacific ocean brings cool, humid air
to the East Coast.
• From North Atlantic ocean brings cool
humid air to the West Coast.
•cT
–Continental
Tropical
Hot dry Air
originating
over desert
areas
Continental Tropical
• Brings hot and dry air from Southern and
Northern Mexico to Northeast and Southern
Great plain states.
Continental Polar
• Brings cold and dry air from over Canada
and Alaska to Central and Eastern United
States.
•cP
–Continental
Polar
Cold dry air
coming
from high
latitudes
Name the air mass that will influence our weather.
When 2 air masses meet, they do not mix. What
happens is that they form a border that is known as a
front. Most of the weather that we think of happens
along fronts.
Fronts
•Any Boundary between
two different air masses
•Generally means a
change in weather
•Four Types
Notice
the
speed of
the cold
front…
Cooler Temperatures
Cold Front Facts
• Occurs when a fast moving cold air mass
overtakes a warm air mass.
• The warm air is forced violently upwards,
causing rapid cooling, vertical cloud
development, and cumulonimbus clouds.
• Often violent thunderstorms but short lived
heavy rain.
• Cooler temperatures behind the front.
Cold Front
Cold Front
• A cold air mass is
replacing a warmer
air mass.
• Shown on a
weather map by a
blue line with
triangles
pointing the
direction the cool
air is moving.
Back to
activity
Cold Fronts
 A cold front forms when a cold air mass
catches up to a warm air mass.
 Colder air is forces the warm air higher
into the atmosphere.
 This warm air that is pushed up cools
and forms clouds. This reaction causes
rain to develop and thunderstorms also
occur along a cold front.
Notice
the
This
speed of
area
is
the cold
where
front…
the
TStorms
are
during
this
front.
Green is
rain.
Notice
the
speed of
the cold
front…
Cooler Temperatures
Warm Front
Warm Front Facts
• This front occurs when a slow moving
warm air mass overtakes a cold air mass.
• The slope on this front is gradual, not steep
like the cold front.
• This slope promotes horizontal
development of clouds and long steady rain.
• High cirrus is usually seen before the warm
front arrives.
• Clear & warm weather follow this front
Warm Front
Warm Front
Back to
activity
• Warm air mass
replacing a
cooler air mass.
• Shown on a
weather map by a
red line with half
circles pointing
the direction the
warm air is
moving.
MAP TAP 2002-2003
Weather Fronts
27
A warm front is when a warm air mass catches up to a cold air mass. (
Just the opposite of a cold front.)
Warm air slides over the cold, dense air. This also causes clouds to
form, but many miles ahead of the front. As the front approaches
and passes it can cause steady rain or snow to fall. After all of this
happens, the sky becomes clear (without clouds) and this is also
when the temperature starts to rise (get higher).
There it
is, and
this is
the area
of
steady
rain.
Stationary Front
Stationary Front Facts
• The front is not in a hurry, it is very slow or not
moving.
• This front occurs when a cold air mass collides
with a warm air mass and does not move.
• None of the air masses are overtaking the other.
• This usually means really long periods of clouds
and steady precipitation.
• The symbol for this front is alternating blue
triangles and red half-circles facing in opposite
directions.
Stationary Front
A front that stops moving is called a stationary front. This type of front can stay in the
same place for days.
When this front stays in the same place for a long time there is constant snow or rainfall
and this leads to several inches of snow or it could even cause a flood.
Occluded Fronts
• When a warm front
is trapped by 2 cold
fronts.
• Shown on a weather
map by a purple
line with alternating
triangles and
semicircles pointing
the direction the
front is moving.
MAP TAP 2002-2003
Weather Fronts
34
Occluded Front Facts
• Very violent type of front.
• This is when 2 cold air masses “pinch together”
and force a warm air mass off of the ground and
higher
• Rapid vertical and horizontal development occurs
and violent storms are created.
• Long and heavy rain with thunder storms.
• The symbol for this front is alternating purple
triangles and half-circles pointing in the direction
that the front is moving.
Occluded Front
Where are the Fronts?
L
Where are the Fronts?
L
H
L
High pressure
brings dry and
clear weather
Low pressure
brings clouds
and rain
There it is, and
this is the area
of steady rain.
So what did you learn?
Summarize information about air masses and
fronts on your paper.