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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
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