Making The
Weather!
Pressure and Fronts
Let’s get it started!!
 So . . . . A couple questions for you . . . .
 Brainstorm this with your table mates. . . . .
 What causes the weather?
 Any idea?
 It’s not any easy question.
 But, we’ll say this – the weather on Earth starts with the sun.
The sun causes water to evaporate and air to move. Those
two things help create our weather.
Under pressure!!
 Much of the weather we experience each day is because of
air pressure.
 Yes . . . . Air pressure. The air that surrounds you – even
though you can’t see it – has weight! And it’s pressing on
you! Even right now!!
 Your body doesn’t collapse because there is air inside you
pushing outward just as hard as the air outside you is
pressing inward!!
Air Pressure & The Weather
 Air acts differently when it is under different amounts of
pressure.
 Air masses – or systems – are large masses or air that have
similar qualities. And they move around!
 High Pressure System
 Air pressure is greater than air pressure around it
 High pressure air pushes into areas of low pressure
 This gets the air moving and causes winds!!
 Cool, dry air
Take it down low!!
 Low Pressure Systems
 These air masses have lower air pressure – and less density -
than high pressure air masses.
 They get pushed around by high pressure systems!
 Low pressure air is warmer and also carries more water
vapor.
 When high pressure air pushes low pressure air around, it
usually goes UPWARD, taking the water vapor with it to form
clouds and, eventually, rain!!
Don’t be frontin’!!
 When we try to predict the weather, we pay attention to
these air masses as the move around.
 When one air mass hits another air mass, it creates what
we call a front. A front is simply the boundary between
two air masses where they meet.
 We are concerned with two kinds of fronts and the
weather they create:
 Cold Fronts
 Warm Fronts
Stop (Cold) Frontin’!!
 A cold front happens when a cold air masses moves into – and
underneath - a warm air mass.
 Because the cold air mass is denser, it pushes the warm air mass
out of the way.
 The warm air gets pushed UPWARD.
 Guess what . . . . That warm air is carrying lots of water vapor
and, when it gets pushed upwards, it forms lots of
cummulonimbus clouds and we get rain!!
 We usually see a DROP in temperature after the front moves
through.
Cold Fronts
More Cold Fronts
Cold Front On The Map
 A cold front – on a weather map – is usually marked with a
blue line. The teeth point in the direction the air is
traveling.
Stop (Warm) Frontin’!!
 A warm front happens when a warm air mass meets a cold
air mass and pushes over it.
 Remember – the warm is less dense than the cold air. It
cannot push it aside, so it flows up and over it.
 With a warm front, you might see some cirrus clouds –
which, remember, forecast a change in the weather – and
some light precipitation.
 After the warm front pushes through, the temperature will
rise!
Warm Fronts!
Another Warm Front!
Warm Front On The Map
 A warm front – on a weather map – is usually marked with
a red line. The dots point in the direction the air is
traveling.
Were you payin’ ‘tention?
 What causes water to evaporate and air to move?
 High pressure air likes to move into spaces where low
pressure air is. True/False
 Which air mass carries more water vapor – cold or warm?
 High pressure air masses produce nice weather. True/False
 A cold front usually produces what kind of weather?
 A warm front usually produces what kind of weather?