Air Pressure

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

Barometer – tool used to measure air pressure.

High pressure brings mild winds, stable temperatures, and clear weather.

Low pressure brings strong winds, dropping temperatures and precipitation.

H

L

Barometric Pressure – tells us when weather will change.

when it falls - low pressure moving in

when it rises- high pressure moving in

Air P

ressure

L

H

Air

Pre

ssur

eWarm air=

expanding or rising air= leaves

behind L pressure

Cold Air=sinking

air= leaves an area of H pressure

Global Circulation and Wind Global Circulation and Wind SystemsSystems

Global Air Masses

• North America gets 5 types of air masses

• Defined by areas of origination

• Highly variable in terms of temperature and moisture

Air Masses

Air Masses are huge clumps of air that move around the Earth, bringing changes in…

weather. Air masses are like the surface they form over.

Air Mass a huge “bubble” of air that shares the same

temperature and pressure. (can be big enough to cover several states!)

The air mass shown above formed over land in northern Canada.

Therefore the air mass will be…

cold and dry.

Cold Air Mass – this is an air mass made up of cool temperatures and high pressure.

Usually does not hold much moistureForms over cold water or land.

A polar air mass brings cold air

H

The pink air mass formed over the ocean near the equator.

The air mass will be…warm and moist.

Warm Air Mass – this is an air mass made up of warm air that has a low pressure.

Usually holds a lot of moisture.Forms over hot land or water. L

A tropical air mass brings warm air

Fronts

Where air masses meet and do not mix

When two air masses meet, they form a…

front.

During a cold front, a cold air mass catches up to a warm air mass

and… pushes the warm air up

quickly. Weather associated with cold fronts is…

Thunderstorms

See A Cold Front Forming…. Click Here!

When cold air catches up to warm air and pushes it up and away, what is

formed?... cold front

The map symbol for a cold front is a curved

line with small…

blue spikes

From the map above, you can predict that the weather in the southern U.S. will be getting…

colder

See A Warm Front Forming…. Click Here!

When warm air catches up to a cold air mass, what is formed?...

warm front

The map symbol for a warm front is a curved

line with small…

rounded knobs

When a warm air mass catches up with a cold air mass, it forms a…

warm frontThe warm air…

slides over the top of the cold air,

before …pushing it away.

Weather associated with warm fronts are….

Clouds and long periods of steady

rain

From the map above, you can predict that the weather over the Great Lakes

will be getting …

warmer

Warm or cold front stops moving.

Light wind and precipitation may occur across the front boundary

• One front overtakes another• Cold front typically faster moving

• Can have warm and cold occluded fronts• Creates Precipitation

Name the Weather Fronts