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?