Download air mass

 Weather depends on what type of air mass
is over an area and whether or not the spot
is under a front.
 The air masses and how they interact will
determine if the weather is constant or will
be changing in temperature, wind, or
precipitation.
Air Mass
 An air mass is a large body of air that has
nearly the same temperature and humidity.
 It has properties similar to the area over
which it developed.
 They most
commonly form
over polar and
tropical
regions.
 The temperate
zone (where
the US is) is
too unstable for
air masses to
form.
 An air mass will
carry its
characteristics
as it travels
and will share it
with whatever it
is over.
 This cold, dry
air mass from
the polar region
is cooling down
all the cities in
its path.
 The polar vortex was the result of the arctic
air mass moving further south than usual
Classifying Air Masses
 Four major types of
air masses influence
the weather in North
America:
– maritime tropical
– continental
tropical
– maritime polar
– continental polar.
North American Air Masses
 Polar air masses flow towards the equator
 Tropic air masses flow towards the poles.
 They move due to pressure differences.
 When 2 or more different air masses meet,
this is called a front.
 When 2 air masses have different
temperatures and different humidity levels,
they will have different densities.
 Objects with different densities do not mix
easily
 One air mass will be lifted above another
 When air masses are lifted, clouds may
form, precipitation may fall, wind and
thunderstorms may occur.
 Fronts are the main cause of stormy
weather.
 There are four main types of fronts
Cold Front
• Occurs when colder air (more dense)
advances toward warm air (less dense).
• Cold air wedges under warmer air.
Cold Front
 Warm air is lifted, it cools, and water vapor
condenses, forming clouds.
 If there is a large temperature difference,
thunderstorms and tornadoes may form
Cold Front
Click to see
animation!
 Clouds can indicate what type of front is
occurring.
Warm Front
 Forms when lighter, warmer air advances
over heavier, colder air.
Warm Front
 May result in hours or days of wet weather
http://stream2.cma.gov.cn/pub/comet/FireWeather/S290Unit6Atmosp
hericStability/comet/fire/s290/unit6/media/flash/2-2.4.0.pop2.htm
Warm Front
 Clouds can
help us figure
out what type
of front is
approaching.
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one.com/books/ea
rth_science/terc/c
ontent/visualizatio
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on
Stationary Front
 Occurs when a boundary between air
masses stops advancing.
Stationary Fronts
Stationary Front
 May stay in place for
days
 Light wind and
precipitation
Occluded Front
 Forms when air masses of three different
temperatures meet up.
 A cold air mass moves toward a cool air with warm
air between the two. The colder air forces the
warm air upward.
Occlusion
Front
COOL AIR
•Weather
can be
especially
fierce at the
occlusion
Comparing and Contrasting
 compare and contrast the four types of fronts
by completing a table like the one below.
Front
How It Forms
Cold front
A cold air mass
overtakes a warm air
mass.
A warm air mass
overtakes a cold air
mass.
Cold and warm air
masses meet, but neither
can move the other.
A warm air mass is caught
between two cold air
masses.
Warm front
Stationary front
Occluded front
Types of
Weather
Clouds, possibly storms
with heavy precipitation
Clouds, light
precipitation
Clouds, precipitation
Clouds, precipitation
Compare the fronts- animations
 http://www.phschool.com/atschool/phsciexp/
active_art/weather_fronts/
Summary of Fronts
High and Low Pressure Areas
• High pressure
causes air to sink
• Usually results in
several days of clear
sunny skies
• Air rises in low
pressure areas and
forms water
droplets
• Usually results in
rain and storms